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Sensing Performance of Multi-Channel RFID-based Finger Augmentation Devices for Tactile Internet

F. Naccarata, G. M. Bianco, G. MarroccoIEEE Journal of Radio Frequency Identification - accepted for publication

Radiofrequency finger augmentation devices (RFADs) are a recently introduced class of epidermal radiofrequency identification (RFID) sensor-tags attached to the fingers, communicating with a body-worn reader. These devices are promising candidates to enable Tactile Internet (TI) applications in the short term. R-FAD based on auto-tuning RFID microchips can be used as dielectric probes for the material of touched objects. However, due to the nearly unpredictable intrinsic variability of finger-object interaction, a single sensorized finger (single-channel device) is not enough to guarantee reliable data sampling. These limitations can be overcome by exploiting a multi-channel R-FAD sensorizing multiple fingers of the hand. In this paper, the dielectric-sensing performance of a multi-channel R-FAD, composed of sensors encapsulated into soft elastomers, is numerically and experimentally characterized, involving a set of volunteers. The inter-sensor coupling is negligible, thus enabling simultaneous independent dielectric measurements. The multi-sensor configuration allows for 100% reliability of the onhand communication link for touched objects in a wide range of permittivity. Experiments moreover demonstrate that multi-channel measurements can halve the measurement uncertainty of the single-channel case. The achievable precision is suitable to discriminate among low-, medium-, and high-permittivity materials.

Numerical and Experimental Characterization of LoRa-based Helmet-to UAV links on Flat Lands

G. M. Bianco, A. Mejia-Aguilar, G. MarroccoIEEE Antennas and Propagation Magazine - accepted for publication

The use of the LoRa communication protocol in a new generation of transceivers is attractive for search and rescue (SaR) procedures because they can operate in harsh environments covering vast areas while maintaining a low power consumption. The possibility of wearing helmets equipped with LoRa-radios and installing LoRa transceivers in unmanned aerial vehicles (UAVs) will accelerate the localization of the targets, probably unconscious. In this paper, the achievable communication ranges of such links are theoretically and experimentally evaluated by considering the possible positions of the helmet wearer (standing or lying) on a flat field, representing a simple SaR scenario. Simulations and experimental tests demonstrated that, for the standing position, the ground-bounce multi-path produces strong fluctuations of the received power versus the Tx-Rx distances. Such fluctuations can be kept confined within 100 m from the target by lowering the UAV altitude. Instead, for a more critical lying position, the received power profile is monotonic and nearly insensitive to the posture. For all the considered cases, the signal emitted by the body-worn transceiver can be exploited to localize the helmet wearer based on its strength, and it is theoretically detectable by the UAV radio up to 5 km on flat terrain.

Automatic Monitoring of Fruit Ripening Rooms by UHF RFID Sensor Network and Machine Learning

C. Occhiuzzi, F. Camera, M. D’Orazio, N. D’Uva, S. Amendola, G. M. Bianco, C. Miozzi, L. Garavaglia, E. Martinelli, G. MarroccoIEEE Journal of Radio Frequency Identification - early access

Accelerated ripening through the exposure of fruits to controlled environmental conditions and gases is nowadays one of the most assessed food technologies, especially for climacteric and exotic products. However, a fine granularity control of the process and consequently of the quality of the goods is still missing, so the management of the ripening rooms is mainly based on qualitative estimations only. Following the modern paradigms of Industry 4.0, this contribution proposes a nondestructive RFID-based system for the automatic evaluation of the live ripening of avocados. The system, coupled with a properly trained automatic classification algorithm based on Support Vector Machines (SVMs), can discriminate the stage of ripening with an accuracy greater than 85%.

Design and Experimental Characterization of On-skin Loop Antenna for Next 5G Backscattering-based Communications
C. Occhiuzzi, F. Romoli Venturi, F. Amato,  A. Di Carlofelice,  P. Tognolatti, G. Marrocco,  IEEE Journal of Radio Frequency Identification - early access

Backscattering-based communications are promising solutions for large scale body-centric monitoring systems, for the low power requirements and the simple and lightweight electronics. Currently, UHF frequency band represents the golden standard, mainly thanks to the well assessed Radio Frequency IDentification (RFID) technology. However, early studies proposed the exploitation to the upcoming 5G communication infrastructures to overcome the limitations in bit-rate and bandwidth and the need of a dedicated reading platform to interact with the tags. The aim of the work is to experimentally verify, from the antenna perspective, the possibility to adopt the 5G 3.6 GHz frequency band also for the next generation body-centric backscattering systems. An epidermal loop antenna is hence designed and prototyped. Measurements in real conditions, e.g. on the human body and through a custom testbed emulating a real backscattering link, are presented as well as statistical analysis on human variability. Results over five volunteers confirm the possibility to read the epidermal tag up to 1.2 m, hence enabling monitoring within a medium-size room.

Folded Comb-line Array for Backscattering-based Bodycentric Communications in the 5G sub-6 GHz Band
C. Occhiuzzi, J. D. Hudges, F. Romoli Venturi, J. Batchelor, G. Marrocco,  IEEE Transactions on Antennas and Propagation - early access

Growing interest in IoT and Healthcare pushes the exploration of innovative solutions for connecting our bodies to external systems. The need for devices interoperability combined with data rate considerations, and low power consumption make 5G backscattering-based communications a promising opportunity, especially in the low sub-6 GHz band. Starting from a monolithic array, this paper proposes a skin-mountable miniaturized antenna suitable for 3.6 GHz body-centric backscattering communications. The array is an improved version of the combline antenna, which simultaneously optimizes size and radiation features. The horizontal segments are folded such to place the radiating dipoles closer and increase the radiation efficiency of the structure by co-phasing a single component of the surface currents. Parametric analysis obtains optimal configurations in terms of gain and size. Compared to conventional layout, the miniaturized array has an efficiency 6 dB higher and an area 80% smaller while the improved structure provides a theoretical read distance of more than 4 m. Measurements on a volunteer corroborate the improved performance.

A Survey on Radio Frequency Identification as a Scalable Technology to Face Pandemics
G.M. Bianco, C. Occhiuzzi, N. Panunzio, G. Marrocco,
IEEE Journal of Radio Frequency Identification

The COVID-19 pandemic drastically changed our way of living. To minimize life losses, multi-level strategies requiring collective efforts were adopted while waiting for the vaccines’ rollout. The management of such complex processes has taken benefit from the rising framework of the Internet of Things (IoT), and particularly the Radiofrequency Identification (RFID) since it is probably the most suitable approach to both the micro (user) and the macro (processes) scale. Hence, a single infrastructure can support both the logistic and monitoring issues related to the war against a pandemic. Based on the COVID-19 experience, this paper is a survey on how state-of-the-art RFID systems can be employed in facing future pandemic outbreaks. The three pillars of the contrast of the pandemic are addressed: 1) use of Personal Protective Equipment (PPE), 2) access control and social distancing, and 3) early detection of symptoms. For each class, the envisaged RFID devices and procedures are discussed based on the available technology and the current worldwide research. This survey that RFID could generate an extraordinary amount of data so that complementary paradigms of Edge Computing and Artificial intelligence can be tightly integrated to extract profiles and identify anomalous events in compliance with privacy and security.


Near field Circular Array for the Transcutaneous Telemetry of UHF RFID based Implantable Medical Devices
C. Miozzi, G. Saggio, E. Gruppioni, G. Marrocco,
IEEE Journal of Electromagnetics, RF and Microwaves in Medicine and Biology - early access

Wireless communication with Implantable Medical Devices (IMDs) based on Radiofrequency Identification in the UHF band suffers from the constraints on the maximum power absorbed by the body tissues. Accordingly, an interrogating antenna placed onto the skin is capable to monitor only a limited region just below its footprint. In some applications like the hand prosthesis controlled by Electromyographic signals emitted by muscle contractions, multiple IMD shave to be used to increase the degrees of freedom in driving the actuators. An array of interrogators, working in the near-field can mitigate this bottleneck by greatly extend the read region inside the body. Sequentially- and simultaneously-fed arrays by a same reader are here investigated to optimize the multi-sensor backscattering modulated links. The conditions (feeding scheme and alignment) to guarantee a robust interrogation of a relevant number of implanted sensors with no battery on board are identified also accounting for the safety constraints related to the SAR. Numerical simulations and experimentation with a cylindrical phantom resembling human limbs, hosting reference antennas, demonstrate that the simultaneous feed permits to interact with eight IMDs by using nearly all the available power from typical readers (30 dBm, 22 dBm as a minimum) without exceeding the SAR limit with a power margin (w.r.t. sensor-oriented ICs with -10dBm power sensitivity) of more than 5 dB for any angular alignment between the array and the sensors.

A Fractal-RFID Based Sensing Tattoo for the Early Detection of Cracks in Implanted Metal Prostheses
S. Nappi, L. Gargale, F. Naccarata, P.P. Valentini, G. Marrocco,
IEEE Journal of Electromagnetics, RF and Microwaves in Medicine and Biology

Manufacturing faults and aging are the main causes for micro-crack generation in implanted prostheses. An early detection of surface defects by means of local sensors can prevent dangerous complications and prompt for a preventive replacement of the medical device. For this purpose, a tattoo-like sensing mechanism based on pre-fractal Space Fulling Curves is wrapped onto the medical device and coupled with a zero-power RFID transponder. The resulting smart prosthesis is capable to identify the early formation of cracks and to communicate with the exterior of the body by backscattering communication. The crack detection method exploits the anti-tamper port of common Radiofrequency Identification (RFID) ICs and a small antenna, acting as harvester, closely integrated with the metal prosthesis. Simulations and tests with a mockup of metallic hip prosthesis and a leg phantom demonstrate that the device can identify surface cracks as small as 0.6mmand can be wireless interrogated outside the body fromup to 70cmdistance. The required geometrical change to the prosthesis is modest and does not hinder its mechanical robustness. Experiments also confirmed that the health status of the prosthesis could be even monitored on-the-fly when the patient crosses a door equipped with a UHF reader. The sensorized prosthesis could hence become an enabler for the emerging Precision Medicine and for the Internet of Bodies paradigm.

Multi-slope Path Loss and Position Estimation with Grid Search and Experimental Results
G.M. Bianco, R. Giuliano, F. Mazzenga, G. Marrocco,
IEEE Transactions on Signal and Information Processing over Networks

A transmitting device can be localized based only on the received signal strength (RSS) measured by receivers. Typical RSS-based algorithms assume the a priori knowledge of the path loss (PL) the signal undergoes in the search area. Recently, algorithms removing this assumption have been introduced based on statistical and nonlinear methods to solve the optimization problem required to estimate the transmitter’s position. However, such nonlinear methods could not converge to the optimal solution, especially in scenarios characterized by multislope or angular dependent PL. This paper considers an exhaustive search algorithm (ESA) for network localization based on the weighted least square (WLS) minimization. The algorithm’s effectiveness is assessed by simulation and compared with the derived Cramér-Rao lower bound (CRLB). From experiments with very noisy measurements in indoor and outdoor, the localization error with 200 PL measurements employing the LoRa protocol is 5 m, whereas algorithms assuming a single slope incur errors between 12 m and 47 m.

Antennifying Orthopedic Bone-Plate Fixtures for the Wireless Monitoring of Local Deep Infections
P. Avaltroni, S. Nappi, G. Marrocco,
IEEE Sensors Journal

Infection is the unavoidable threat to any orthopedic implant that can also force its removal as extreme remedy. The diagnosis of infections is currently achieved by time consuming imaging (X-Rays, MRI, CT) or just by the onset of the patient’s pain, when the problem is in an advanced status. Instead, by equipping the prosthesis with a local sensor (for the temperature as a first) and with a wireless communication radio, an earlytime identification of the infection could be achieved. This paper proposes a method to transform an orthopedic device provided with holes (like a bone fixation plate) into an harvesting antenna integrating an RFID sensor, with no battery onboard. A miniaturized antenna adapter, fully embedded into a free hole, with tuning capability, collects the electromagnetic power intercepted by the medical device and transfers it to the RFID circuit. Simulations and experimentations with several prototypes demonstrated that the augmented implanted device can establish a stable RFID link up to 0.5 m and that it is able to correctly sample the variation (37°C - 40°C) of the local temperature of the bone as in case of typical deep infections.

Propagation modeling inside the International Space Station for the automatic monitoring of Astronauts by means of Epidermal UHF-RFID Sensors
N. Panunzio, C. Occhiuzzi, G. Marrocco,
IEEE Journal of Radio Frequency Identification

The monitoring of Astronaut’s health is one of the most impacting aspects of long-duration Space missions, especially for the high involvement required to the crew members in the daily acquisition of body parameters. Automatic procedures based on wireless systems would grant undeniable benefits, especially if lightweight and battery-less devices could be adopted. The possibility and the reliability of a communication link inside the International Space Station (ISS) is here investigated when the UHF-RFID epidermal technology is adopted. A Ray Tracing asymptotic method is hence proposed to evaluate the coverage area and the read probability inside the Harmony module. The analysis is referred to up to two astronauts simultaneously present in the module and to the presence of multiple reader antennas, in case purely passive epidermal tags are adopted. Simulations revealed that it is possible to identify some simple operating conditions that allow to obtain a reliable RFID link, also thanks to the advantageous propagation characteristics of the module itself.

Sensorized facemask with moisture-sensitive RFID antenna
G.M. Bianco, G. Marrocco,
IEEE Sensors Letters

Due to the ongoing COVID-19 pandemic, the use of Filtering Facepiece Respirators (FFRs) is increasingly widespread. Since the masks’ wetness can reduce its filtering capabilities, the World Health Organization advises to replace the FFRs if they become too damp, but, currently, there is no practical way to monitor the masks’ wetness. A low-cost moisture sensor placed inside the FFRs could discriminate a slightly damp mask from a wet one which must be replaced. In this paper, a RadioFrequency Identification (RFID) tag exploiting an auto-tuning microchip for humidity sensing is designed and tested during an ordinary working day and a physical exercise. The tag returns about 1 unit of the digital metric every 3 milligrams of water generated by breathing and sweating, and it can identify excessively wet masks from commonly used ones.


Medium-distance affordable, flexible and wireless epidermal sensor for pH monitoring in sweat
V. Mazzaracchio, L. Fiore, S. Nappi, G. Marrocco, F. Arduini, Talanta, vol.222

In the last decade, wearable sensors have gained a key role on biomedical research field for reliable health state monitoring. A wide plethora of physics marker sensors is already commercially available, including activity tracker, heart rate devices, and fitness smartwatch. On the contrary, wearable and epidermal sensors for chemical biomarker monitoring in several biofluids are not ready yet. Herein, we report a wireless and flexible epidermal device for pH monitoring in sweat, fabricated by encompassing a screen-printed potentiometric sensor, an integrated circuit, and antenna embedded onto the same Kapton substrate. An iridium oxide film was electrodeposited onto the graphite working electrode providing the pH sensitive layer, while the integrated circuit board allows for data acquisition and storing. Furthermore, a radio frequency identification antenna surrounding the entire system enables data transmission to an external reader up to nearly 2 m in the most favourable case. The potentiometric sensor was firstly characterised by cyclic voltammetry experiments, then the iridium oxide electrodeposition procedure was optimised. Next, the sensor was tested toward pH detection in buffer solutions with a near-Nernstian response equal to −0.079 ± 0.002 V for unit of pH. Interference studies of common sweat ions, including Na+, K+ and Cl−, showed any influence on the pH sensor response. Finally, the integrated epidermal device was tested for real-time on-body pH sweat monitoring during a running activity. Data recorded for a running subject were wireless transmitted to an external receiver, showing a pH value close to 5.5, in agreement with value obtained by pH-meter reference measurement.

Experimental Assessment of Wireless Monitoring of Axilla Temperature by means of Epidermal Battery-less RFID Sensors
F. Camera, C. Miozzi, F. Amato, C. Occhiuzzi, G. Marrocco, IEEE Sensors Letters

Wireless epidermal devices (WED), based on UHF Radio frequency Identification (RFID), enable a contactless and non-invasive human body monitoring through sampling of health parameters directly on the skin. With reference to body temperature, this letter reports an experimental campaign aimed at assessing the degree of agreement of a batteryless plaster-like WED, placed in the armpit region, with a standard axilla thermocouple thermometer. A measurement campaign over 10 volunteers, for overall 120 temperature outcomes, revealed a good correlation among the instruments (Person’s coefficient p=0.78) and a difference of less than 0.6°C in the 95% of the measured cases, provided that a user-calibration is applied. RFID-WED enables a non-contacting reading up to 20 cm and a direct connectivity with a cloud architecture. Envisaged applications are the periodic monitoring in clinical and domestic scenarios, as well as the screening of restricted communities related to Covid-19 control and recovery.

RFID-based Dual-Chip Epidermal Sensing Platform for Human Skin Monitoring
C. Occhiuzzi, S. Parrella, F. Camera, S. Nappi, G. Marrocco, IEEE Sensors

Wireless epidermal devices based on Radio frequency Identification (RFID) enable a contactless and noninvasive monitoring of the human body by sampling health parameters directly on the skin. To achieve multi-parametric sensing, while preserving the intrinsic simplicity and the low cost of RFID tags, a dual-chip epidermal device is here proposed. At this purpose a polarization-diversity loop antenna is exploited so that two almost independent current modes are excited. The resulting radiation patterns are both broadside, thus enabling the simultaneous gathering of two independent dataset from the same maximum distance. A 3.5 by 3.5 cm battery-less, flexible and soft prototype provides -13 dBi embedded realized gain with read distances ranging from 0.6m to 1.5m depending on the microchip sensitivity. The electromagnetic performance of the two ports remain similar even when the tag is applied onto rather in-homogeneous body regions. With reference to body temperature monitoring, the device has been experimented in both controlled and real-life environments, demonstrating the possibility of doubling the sensing capabilities of RFID epidermal devices without affecting their size and radiation performances.

Twin Grid-array as 3.6 GHz Epidermal Antenna for Potential Backscattering 5G Communication
J. Hughes, C. Occhiuzzi, J. Batchelor, G. Marrocco, IEEE Antenna and Wireless Propagation Letters, Early Access

Emerging 5G infrastructures can boost innovative paradigms for future wearable and epidermal devices exploiting low-power (even passive) wireless backscattering-based communication.Tocompensatehighbody-andpath-losses,andtoextend the read range, array configurations are required. This work proposes a flexible monolithic epidermal layout, based on Krauss array concept, that operates at 3.6 GHz and it is suitable to be directly attached to the human body. The antenna involves a dual grid configuration with a main radiating grid backed by a grid reflector placed in touch with the skin. Overall, the amount of conductor an dielectric substrate are minimized with benefittobreathability.Theantennaissuitabletosurfacefeeding and produces a broadside radiation. Parametric analysis are performed and an optimal configuration of four-cells grid is derived and experimentally demonstrated to provide a maximum gain of more than 6 dBi.

LoRa System for Search and Rescue: Path Loss Models and Procedures in Mountain Scenarios
G. M. Bianco, R. Giuliano, G. Marrocco, F. Mazzenga, A. Mejia-Aguilar, IEEE Internet of Things Journal, in press

Typical mountain Search and Rescue (SaR) operations require the localization of the persons involved in accidents in harsh environments. ARVA and RECCOr are the current standards for the localization in snowy environments although their radio range is limited to some tens of meters. In this paper, we prove by experimental results that the Long Range (LoRa) Low-Power Wide-Area Network (LPWAN) technology is very promising for SaR applications due to its extended radio range. A LoRa-based system for SaR operations is presented and analyzed. The localization of the persons is obtained through an algorithm based on path loss measurements. Radio path loss models of body-worn LoRa devices in harsh mountain environments are derived by measurements.We observed that, although the communication range of LoRa decreases from kilometres to hundreds of meters in the tested environments, at least 50% of the transmitted packets can be received at distances about five times greater than those achievable with golden standard technologies such as ARVA. The performances of the considered localization algorithm are analyzed on the basis of the collected data. The achievable accuracy is in the order of meters around the true position for a relatively large number of available path loss measurements. Lastly, we propose and detail a LoRa-based system for SaR operations.

Radio-Frequency-Identification-Based Intelligent Packaging
C. Occhiuzzi, N. D'Uva, S. Nappi, S. Amendola, C. Gialluca, V. Chiabrando, L. Garavaglia, G. Giacalone, G. Marrocco, IEEE Antennas and Propagation Magazine, in press

Intelligent packaging for food continuously generates informative digital/analog content about the contained products during their entire life span, thus becoming one of the enabling elements of the modern data-driven economy. Packaging shells for fruits, augmented with low-cost wireless sensors for the automatic estimation of the ripening grade, can reduce waste, optimize shelf exposure, suggest when produce should be consumed, and engage customers through enhanced user experiences. Radio-frequency identification (RFID) with sensorless, low-cost labels, empowered with electromagnetic-based intelligence and automatic classification tools, may stimulate the widespread diffusion of this technology. Focusing on avocados, this article presents an experimental characterization of RFID’s complex permittivity along with ripening and a nearfield numerical model of a passive RFID interrogation system with tagged fruit, aimed at extracting the variation of electromagnetic metrics of the RFID link during ripening. The results are used to design and fabricate an RFID totem for avocado monitoring that, coupled with a properly trained binary tree classifier, is capable of recognizing up to three ripening levels of packaged fruits, with an overall accuracy higher than 85% even if the task is executed by unskilled operators.

Electromagnetic-based Correction of Bio-Integrated RFID Sensors for Reliable Skin Temperature Monitoring

F. Camera, G. Marrocco, IEEE Sensors, in press

Bio-integrated wireless sensors in the form of conformable plaster, based on the Radiofrequency Identification (RFID) communication, have been recently proposed for the battery-less measurement of the human skin temperature. However, the response of the Integrated Circuit (IC) transponder is sensitive to the strength of the interrogating power. Indeed, high power produces artifacts on the sampled temperature up to 2 °C when the mutual position between reader and sensors, as well as the emitted power, can not be carefully controlled. Hence, a reliable adoption of this technology in real cases is challenging and still in question. A combined macro-scale electromagnetic-thermal model is here introduced to predict and correct the above artifact so that the temperature measurement becomes insensitive to the RF power collected by the IC. The method is based on the new generation RFID ICs with on-chip temperature sensor that are also capable to give back the strength of the collected RF power. The model is validated in controlled conditions and then applied for different skin temperature measurements on human body. An average accuracy of 0.25 °C, compared with a reference calibrated thermocouple, was demonstrated in the considered tests.

Performance and Durability of Thread Antennas as Stretchable Epidermal UHF RFID Tags

C. Miozzi, F. Amato, G. Marrocco, IEEE Journal of RFID, June 2020, Early Access

Epidermal sensors based on battery-less Radiofrequency Identification (RFID) aim at collecting biophysical parameters with a high level of comfort for the user. This paper investigates the performance and durability of epidermal RFID tags, equipped with a self-tuning RFID IC, that are based either on copper wires or conductive yarn. The tags are deployed onto an ultra-thin stretchable and transparent substrate to achieve comformability to body discontinuities. A statistical analysis on volunteers showed that, in the whole UHF band (860-960 MHz), reliable read ranges of 1 m are easily achieved while up to 2 m can be reached in some favorable configurations. Both tags withstand wear, mechanical stress due to the movements of the body, sweating, and water. In particular, the tag made of conductive yarn lasts for more than 20 days. This new family of epidermal tags are moreover suitable to low-cost and large-scale manufacturing through the widely available machines used for wire-laying, bending, and shaping.

Near-field Constrained Design for Self-tuning UHF-RFID Antennas

G. Bianco, S. Amendola, G. Marrocco, IEEE Transactions on Antennas and Propagation, May 2020, Early Access

Recently introduced self-tuning RFID tags are capable to dynamically modify the input impedance of the embedded microchip transponder in order to compensate possible impedance mismatch with the antenna, thus making the communication performance rather insensitive to the nearby environment. A general method for the design of this new class of tags is presented with the purpose to master the complex configuration, where the tag is placed at a close distance from the interrogating antenna and the free-space assumption is not valid. A two-port system is introduced and the networkoriented reformulation of self-tuning action permits to derive an optimization problem for the minimization of the interrogation power for a wide range of boundary conditions. The method is demonstrated, both numerically and experimentally, through the application of a Finger Augmentation Device aimed to achieve a smart interaction with touched objects.

Epidermal Backscattering Antennas in the 5G Framework: Performance and Perspectives

F. Amato, C. Occhiuzzi, G. Marrocco, IEEE Journal of RFID, May 2020, Early Access

Epidermal RFIDs, if integrated within the nextgeneration (5G) wireless architecture, would enable low-cost healthcare applications for remote monitoring of patients, realtime telesurgery, and augmented sensing abilities. This paper explores, through simulations and preliminary experiments, epidermal 5G-RFIDs operating both at microwave and mmWave frequencies. In particular, it identifies the maximum gains of epidermal antennas at their optimal sizes, the achievable read ranges of passive 5G-RFID links, and their possible data-rates. Moreover, it demonstrates the compliance with electromagnetic exposure regulations and explores the benefits of epidermal arrays. Loop transponders at microwave frequencies (3.6 GHz) could provide the same read distance (one meter) of their UHF counterparts while having a smaller footprint (17 x 17 mm2) and reaching a theoretical data-rate as high as 0.5 Gbps. At 28 GHz and 60 GHz, instead, arrays could be used to both achieve comparable performances and enable beamsteering.

C. Miozzi, G. Diotallevi, M. Cirelli, P. P. Valentini, G. Marrocco, IEEE Sensors, Jan. 2020, Early Access

Recent developments in Materials and Radiofrequency Identification (RFID) technologies are currently boosting the development of new class of flexible and elastic epidermal devices for the wireless remote monitoring of biophysical parameters. As tightly bio-integrated with the skin, epidermal antennas are subjected to mechanical deformation during the natural movements and gestures of the human body. The experienced effect is a degradation of the communication performance of the RFID link. In this contribution, we evaluate the stiffness and the change of the radiation gain of on-skin UHF antennas in common gestures by a combined mechanical-electromagnetic model to provide a database and a modelling methodology to improve the design of deformation-tolerant skin antennas. The deformation of the skin is firstly quantified by using a contactless 3D scanner and then the communication impact is predicted by means of an electromagnetic analysis of stretched antennas for some relevant cases of thin-wire layouts. Preliminary numerical simulations and experimentations demonstrated that constraints over low stiffness and insensitivity of radiation gain could be not always compatible. An epidermal antenna may undergo up to 3-4 dB of gain degradation that converts to 30% reduction of the read distance for the strain orientation producing the minimum mechanical stiffness. The derived deformation database could be useful to improve the design of more robust epidermal antennas.

Application of Wireless Technologies in a Nuclear Plant: Evaluation of Electromagnetic Propagation With Different Computational Techniques

M. Cappelli, V. Lopresto, R. Cecchi,
and G. Marrocco, IEEE Journal of Nuclear Engineering and Radiation Science, vol. 6, April 2020

The aim of this work is to present a preliminary investigation on the propagation of electromagnetic fields generated by wireless technologies inside a nuclear facility or power plant. First, a survey of currently proposed wireless technologies for nuclear facilities and plants has been carried out. Then, for selected scenarios, the electromagnetic field propagation has been studied by means of electromagnetic simulation tools, and the presence of the nuclear environment has been simulated by properly modeling environmental parameters and engineered barriers. The choice of the proper simulation techniques and tools is mandatory in order to simulate the effect of the realistic environment on the propagation. Accordingly, the feasibility of wireless technologies application at nuclear facilities can be assessed on the basis of results achieved from simulated scenarios. The goal is to analyze, for selected scenarios, possible issues due to the propagation of an electromagnetic field in the presence of simplified barriers mimicking the real nuclear environment. This approach can provide indications on how to deploy potential benefits of wireless technologies in a nuclear environment, evaluating pros and cons of the investigated technologies.


Space-Filling Electromagnetic Skins for the Wireless Monitoring of Surface Defects

S. Nappi and G. Marrocco, IEEE Sensors, August 2019, Early Access

Polymer-based objects (cable harness, gaskets, tires) are exposed, during their lifetime, to mechanical and chemical stress that often generates surface defects like crack and scratches. Early detection of signs of aging may enable a Predictive Maintenance to extend the life of the object and avoid severe failures. For this purpose, Space Filling Curves (SFC) are here proposed as an artificial electric skin, suitable to envelope a surface to wireless detect the presence of small aging signs by resorting to an electromagnetic backscattering platform. Size and resolution of the skin can be controlled by just two parameters and multiple skin cells can be arranged together to tessellate a large surface in order to even identify the position of the defect. By following a theoretical analysis of the sensor-oriented properties of SFCs, and in particular of the Gosper-Fukuda family, the feasibility of the idea is demonstrated by the way of preliminary experiments with a Radio Frequency Identification (RFID) IC, providing a 1-bit anti-tamper port.

Flexible pH Sensor for Wireless Monitoring of the Human Skin from the Medimun Distances

S. Nappi, V. Mazzaracchio, L. Fiore, F. Arduini and G. Marrocco, IEEE International Conference on Flexible and Printable Sensors and Systems (FLEPS 2019), Glasgow, Scotland (UK), July 7-10, 2019

Sweat monitoring is an effective procedure to detect early signs or precursors of some psychophysical diseases. A compact wireless flexible on-skin pH sensor is here proposed for integration with Radiofrequency Identification in the UHF band. The peculiarity is its simplicity and minimal amount of required electronic components. The device comprises a printed multilayer pH sensor and an energy harvesting antenna optimized for application onto the human skin. Preliminary experiments demonstrated that the device is capable to capture a pH range compatible with physiologic data and to exchange data up to 1m without need of battery.

RF Detection of Micro-cracks in Orthopedic Implants by Conformal Space Filling Curves

S. Nappi, L. Gargale, P. P. Valentini and G. Marrocco, IEEE RFID-TA,
Pisa, Italy, Sept. 25-27, 2019

Implanted prosthesis could be subjected to fractures due to defects and to aging. Conventional diagnostic tools involves X-Rays or, more commonly, the onset of the patient’s pain due to an irreversible failure. A non-invasive wireless monitoring system is here presented for the early detection of micro-cracks over metallic orthopedic implants. The proposed architecture involves a distributed electrode made of Space Filling Curves connected to the anti-tamper port of a UHF RFID transponder. The occurrence of an even small surface crack is detected in a binary form and transmitted remotely, outside the body following a standard RFID interrogation. The feasibility of the idea is supported by numerical analysis and experimental outcomes with a 3D printed and metallized hip prosthesis mockup. Preliminary results demonstrate a detection distance up to 0.7m, fully compliant with fast and non-collaborative diagnosis in the emerging Personalized Healthcare.

Constrained Safety-Integrity Performance of Through-the-Arms UHF-RFID Transcutaneous Wireless Communication for the Control of Prostheses

C. Miozzi, G. Saggio, E. Gruppioni, and G. Marrocco, IEEE Journal of Radio-frequency Identification, June 2019

Advanced prostheses for recovery of arm amputation can be nowadays controlled by the electromyographic (EMG) signals. Implanted myoelectric sensors, suitable to transcutaneous wireless reading, permit to improve the signal-to-noise ratio. This paper explores the feasibility of a through-the-arm telemetry link based on the Radiofrequency Identification in the UHF band (860-960 MHz). The proposed model accounts for the power sensitivity of the commercial devices, the constraints enforced by the exposure regulations (SAR) and by the communication integrity (BER). The reliability of the link is evaluated against possible misalignments between sensors and the reading unit. Results demonstrate that the transcutaneous link can be in some case limited by integrity constraints but can be nevertheless correctly established by means of less than 23 dBm input power (full compatible with embedded readers). The link is moreover robust against angular displacement up to at least  = 35  and linear displacement up to 2.5 cm.

Upper-bound Performances of RFID Epidermal Sensor Networks at 5G Frequencies

F. Amato, S. Amendola, and G. Marrocco, 16th IEEE International Conference on Wearable and Implantable Body Sensor Networks (BSN’19), Chicago (USA), May 19-22, 2019

5G will play a key role in developing high speed wearable and epidermal electronics for healthcare applications such as patient monitoring, tele-surgery, and augmented sensorial abilities (both for humans and robots). At the same time, developing a 5G-RFID system based on backscattering communication will help reducing the power consumption and lowering the electronic complexity. Nevertheless, the high path losses and the strong electromagnetic interactions of the skin might severely limit ranges and performances of epidermal RFIDs operating at 5G frequencies. In this paper, the effects of the human skin on the link budget of epidermal RFID dipoles at microwave and mmWave frequencies are investigated through numerical simulations. Results show that an epidermal RFID sensor tags can reach ranges comparable with UHF systems by using either a single dipole at 5.8 GHz or a 23-element array of dipoles at 60 GHz when using the currently available chip sensitivities (-15 dBm) and reader antenna gains (6 dBi). Smaller antenna sizes of a 5G RFID sensor will allow the integration of tags in new ubiquitous non-invasive epidermal and wearable electronics, while the high frequencies will enable tracking with mm- and micro-scale resolutions for medical applications (e.g.: micro-ablation or muscular and neural rehabilitation).

A General-purpose Configurable RFID Epidermal Board with a Two-way Discrete Impedance Tuning

C. Miozzi, S. Nappi, S. Amendola, C. Occhiuzzi, and G. Marrocco, IEEE Antennas and Wireless Propagation Letters, February 2019

Current advances of the Radiofrequency Identification (RFID) technology can boost the emerging class of biointegrated skin devices exploiting low-power (even passive) wireless communication and sensing interfaces. This work describes a small-size (3cmx3cm) flexible UHF RFID board conceived for the rapid laboratory experimentation and suitable to multi purpose monitoring of physical parameters (e.g. temperature and sweat) over the skin and/or over clothing layers and medical plasters. An engineered open-loop antenna is coupled with a two-way discrete (four states) tuning circuit to compensate the frequency shifts that occur in real applications due to the intrinsic variability of the human body. The capability of the tuning mechanism to down/up-shift the operating frequency and to restore the default state is validated by means of both numerical simulation and measurements over some volunteers in realistic conditions.

Numerical and Experimental Characterization of Wrist-Fingers Communication Link for RFID-based Finger Augmented Devices

S. Amendola, V. Di Cecco, and G. Marrocco, IEEE Transactions on Antennas and Propagation, February 2019

Radiofrequency-Identification Finger-Augmented Devices (R-FAD) identify a particular wearable technology suitable to turn the human fingers into enhanced sensing surfaces to restore lost senses in impaired people as well as to augment the existing ones. The communication channel of R-FAD, involving a reader’s antenna placed onto the wrist and tag antennas stuck onto the fingers, is here characterized in the UHF RFID band by means of both numerical simulations, accounting for several options of the system, and an experimental campaign with volunteers asked to reproduce natural gestures of the hands. The study identifies the most appropriate placement of the devices and, above all, it quantifies the robustness of the link against the human variability. The channel follows a Lognormal Cumulative probability law indicating that the minimum required power to establish a reliable RFID link is 18-27 dBm depending on the chip sensitivity. Measurements finally revealed a remarkable correlation of the minimum required power from the reader with the volume of the hand.


Design and Experimentation of a Batteryless On-skin RFID Graphene-Oxide Sensor for the Monitoring and Discrimination of Breath Anomalies

M. C. Caccami, M. Y. S. Mulla, C. Occhiuzzi, C. Di Natale, and G. Marrocco, IEEE Sensors Journal, August 2018

Real-time and comfortable monitoring of the human breathing could allow identifying anomalies in the rhythm and waveform to be correlated with several pathologic disorders of respiratory and cardiovascular systems. A wireless sensor based on a flexible kapton substrate, suitable to be stuck over the face skin like a plaster and provided with a graphene-oxide (GO) electrode, is here proposed for application to the monitoring of the moisture emitted during inhalations and exhalations. The GO-based electrode increases its DC resistance when exposed to humidity with a sensitivity of 60 Ohm/RH. The device is compatible with the Radiofrequency Identification (RFID) standard in the UHF band. When used in battery-less mode it can be read up to 60 cm. The RFID sensor has been successfully experimented in a measurement campaign involving ten volunteers asked to reproduce a set of predefined normal and pathological breaths. The resulting resistance traces permit to well clusterize the breath patterns with respect to the respiration rate (extracted by an FFT) and to the average peak variation of the sensor’s resistance with an accuracy close to 90%.
cavity A Passive Wireless Sensor Network for the Temperature Mapping Inside a Shielded Coaxial Enclosure

S. Lopez-Soriano, I.P. Spassovsky, J. Parron, and G. Marrocco, IEEE Journal of Radio Frequency Identification

This contribution addresses the electromagnetic feasibility of the wireless temperature monitoring inside a coaxial cavity resembling a portion of a high-power high- frequency Cyclotron Auto-Resonance Maser (CARM) for plasma heating in the new generation of DEMO TOKAMAK machines. The scenario is investigated as a potential communication channel for a UHF RFID sensor network where cavity probes are used to both excite the coaxial cavity and to collect the temperature data scattered back by sensor antennas. By using a theoretical near-field analysis of a simplified model of the cavity and of the reader/sensor devices it is demonstrated that a two-probes architecture is suitable to interact with more than N=16 equally spaced RFID temperature sensors (having power sensitivity of -8.3dBmW) over the surface of a 0.5 m tube by using less than 20dBmW power emitted by the reader. The theoretical results are corroborated by experimental data with a mock-up of the cavity and realistic prototypes of miniaturized RFID radio- sensors and excitation probes.
mesh Inkjet-printed RFID-Skins for the Detection of Surface Defects

S. Nappi, G. Marrocco, URSI AT-RASC, Gran Canaria, June 2018

Hydrogel-based smart wound dressings that combine the traditional favourable properties of hydrogels as skin care materials with sensing functions of relevant biological parameters for the remote monitoring of wound healing are under development. In particular, lightweight, ultra-high frequency radiofrequency identification (UHF RFID) sensor are adjoined to xyloglucan-poly(vinyl alcohol) hydrogel films to battery-less monitor moisture level of the bandage in contact with the skin, as well as wireless transmit the measured data to an off-body reader. This study investigates the swelling behavior of the hydrogels in contact with simulated biological fluids, and the modification of their morphology, mechanical properties, and dielectric properties in a wide range of frequencies (100-106 Hz and 108-1011Hz). The films absorb simulated body fluids up to approximately four times their initial weight, without losing their integrity but undergoing significant microstructural changes. We observed relevant linear increases of electric conductivity and permittivity with the swelling degree, with an abrupt change of slope that is related to the network rearrangements occurring upon swelling.

Development and Characterization of Xyloglucan-poly(vinyl alchohol) Hydrogel Membrane for Wireless Smart-wound Dressing

A. Ajovalasit, M. C. Caccami, S. Amendola, M. A. Sabatino, G. Alotta, M. Zingales, D. Giacomazza, C. Occhiuzi, G. Marrocco, C. Dispenza, European Polymer Journal, Elseview, to appear

The aging of polymer-based objects (tires, cable harness, paints, gaskets) may appear as the formation of surface defects like cracks and scratches. An early detection of such signs may support the Predictive Maintenance of critical polymeric devices before the occurrence of a severe damage. Inkjet printed Space Filling Curves (SFC) are here proposed as an artificial electric skin, suitable to be integrated with an RFID tag, at the purpose to detect and remotely transmit the presence of small aging signs of a surface. Thanks to the particular properties of the Gosper SFC, the size and space resolution of the skin can be easily controlled by few parameters. The idea is corroborated by preliminary experimentations with low-cost inkjet printed traces that easily enable to monitor the presence of a defect from a distance of 10 m and more.

Electromagnetic Modeling of Self-tuning RFID Sensor Antennas in Linear and Nonlinear Regimes

M. C. Caccami and G. Marrocco, IEEE Transaction on Antennas and Propagation, Vol.66 - Early access, March 2018.

Multi-state chips for UHF Radiofrequency Identification ensure self-compensation of the variations in antenna impedance. This self-tuning capability can provide a digital information about the change in local boundary conditions within the vicinity of the tag. This feature can be exploited further for low-cost wireless sensing applications. An electromagnetic model of the tag in linear and nonlinear regimes allows prediction of analog and digital response of the device depending on the boundary conditions that cause the variation of the antenna impedance and/or gain. Additionally, the model provides estimation of the degradation in communication performance of the tag due to imperfect retuning of the chip impedance. The theoretical findings of the model are verified in sensing applications using a reference self-tuning tag. Sensing measurements of liquid compounds in linear regime and of the water-filling level of a box in nonlinear regime are demonstrated as a practical application of the proposed mathematical model.

skin inkjet
Inkjet Printing of Epidermal RFID Antennas by Self-Sintering Conductive Ink 

S. Amendola, A. Palombi, and G. Marrocco, IEEE Transaction on Microwave Theory and Technique,Vol.66, N.3, pp.1561-1569, Mar. 2018.

The recently introduced inkjet printing technology with ambient-sintering is here investigated for the fabrication of epidermal antennas suitable for Radiofrequency Identification (RFID) and Sensing. The attractive feature of this manufacturing process is the possibility to use low-cost printers without any high-temperature curing. In spite of the estimated maximum achievable conductivity of the ink (sigmaUHF = 1 x 105 S/m) in UHF-RFID band is two orders of magnitude lower than that of the bulk copper, a three-fold printing process provides the same on-skin radiating performance as manufacturing technologies using bulk conductors. Experiments demonstrate that the epidermal antennas printed on PET substrate are insensitive to moderate mechanical stress, like the natural bending occurring over the human body, and to the possible exposure to body fluids (e.g. sweat). Moreover, the electromagnetic response remains stable over the time when the printed layouts are coated with biocompatible membranes.


M. C. Caccami, M. Y. S. Mulla, C. Di Natale, and G. Marrocco, IET Microwaves, Antennas & Propagation, 22 Jan. 2018.

The monitoring of the breathing dynamic characteristics, including the presence of biomarkers in exhaled breath, is of growing interest in noninvasive diagnosis of diseases. We describe a wearable radiofrequency identification (RFID) device hosting a flexible antenna suitable for integration into a facemask and a sensor made of graphene oxide sensitive to the humidity variations. The resulting sensor tag was characterized in reference conditions while its communication performance was estimated by electromagnetic simulations as well as measurements over a simplified model of the human head. Finally, the whole system was tested on a volunteer and was experimentally demonstrated to be capable of detecting the inhalation/exhalation cycles and abnormal patterns of respiration like the apnea by measuring the changes in graphene oxide resistance.

tagcopter Ubiquitous Flying Sensor Antennas: Radiofrequency Identification Meets Micro Drones

M. Longhi and G. Marrocco, IEEE RFID Journal, Vol.1, N.4, pp. 291-299, Dec. 2017

Tag-Copter is an architecture of dynamic and selfrelocating sensor devices originating from the synergy between sensor-oriented Radiofrequency Identification (RFID) and the emerging Micro Air Vehicles (MAV) technology. Tag-copters integrate a low-cost nano multi-copter with a miniaturized RFID data-logger antenna for the ubiquitous and cooperative monitoring of indoor volumes as well as of harsh environments. This concept is preliminary exploited by means of a theoretical formulation to derive the upper-bound performance of a flying “winged sensor”. The analysis addresses the sensing accuracy versus the flight speed and the reliability of the on-the-flight data exchange with a fixed base-station through backscattering modulation. A first working 16 g prototype, capable of temperature measurement and storage, is experimented in a controlled setup to corroborate theoretical and experimental findings. The same device is then applied in realistic conditions concerning the temperature mapping within indoor environments. Preliminary results demonstrate that the maximum temperature measurement error is of the order of 1 °C along flight trajectories of 30 m. Finally, most of the data stored within the datalogger memory can be correctly uploaded by a flying tag-copter toward a fixed reader provided that the copter flies at approximatively 1-1.5m from it.

A Tightly Integrated Multilayer BatteryAntenna for RFID Epidermal Applications

M. C. Caccami, M. P. Hogan, M. Alfredsson, G. Marrocco and J. C. Batchelor, Transactions on Antennas and Propagation, November 2017.

For the acceptance of bio-integrated devices in daily life, radio-systems must be developed that are minimally invasive to the skin, and they must have ultra-low profile local power sources to support data-logging functionality without compromising shape-conformability. This contribution proposes a tightly integrated multilayer battery-antenna system (𝟔𝟓    × 𝟐𝟑    𝒎𝒎𝟐) that is ultra-thin (just 𝟐𝟎𝟎    𝝁𝒎), flexible, and lighter than 𝟏    𝒈, making it suitable for epidermal applications. The negative electrode (anode) current collector of the battery is a Radiofrequency Identification (RFID) tag antenna coated by a conductive polymer (Pedot:PSS) working as anode material. Since the battery is a dynamic device, subjected to discharging, the antenna design must include the variable dielectric properties of the conductive polymer that are here first characterized in the UHF band for real charge/discharge battery conditions. The communication performance of the prototype composite device is hence evaluated through the measurement of the realized gain of the tag antenna (-19.6 dBi at 870 MHz) when it is placed directly onto a volunteer's forearm.  The read range of 1.3 - 3 m is suitable for occasional data download from the epidermal data-logger when the user comes close to a reader-equipped gate.

G. Casati, M. Longhi, D. Latini, F. Carbone, S. Amendola, F. Del Frate, G. Schiavon and G. Marrocco, IEEE Journal of Radio Frequency Identification, Vol. 1, N.2, pp. 155-162, Jun. 2017

The combined use of Unmanned Aerial Vehicles and Radiofrequency Identification devices is an emerging topic of the environmental monitoring, which combines the versatility of multi-copter airframes with the potentiality of low-cost wireless sensors. This paper introduces some performance metrics suitable to quantify the capability of an RFIDrone to scan a surface equipped with radio-sensors. By using simple propagation mod- els, an optimal drone-surface distance is mathematically derived at the purpose to maximize the electromagnetic footprint for the specific choice of system parameters, such as the sensor type and position, the reader sensitivity, the ground reflectivity, the radi- ated power and the flight velocity. Theoretical achievements and some preliminary experimentations indicate that omnidirectional antennas are preferred for the drone so that 9-12m footprints could be achieved with state-of-the-art readers and battery-less or battery-assisted RFID sensors, provided that the UAV flights at 3-5 m from the surface to be monitored. In this condition, the hit-rate of arrays of tags is better than 90% for a flying speed less than 1.8 Km/h. The read performance is instead sensibly degraded by the presence of multi path in case of sensors spaced out the surface.

Reliability of a Re-usable Wireless Epidermal Temperature Sensor in Real Conditions

C. Miozzi, S. Amendola, A. Bergamini, and G. Marrocco, 14th International Conference on Wearable and Implantable Body Sensor Networks (BSN 2017), Eindhoven (The Netherlands), 9-12 May 2017.

Body temperature is among most important biometric indicators that are normally checked in both domestic and hospital environments. The way to collect such parameter could be dramatically improved thanks to the Epidermal Electronics technology enabling plaster-like devices suitable to on-skin temperature sensing and capable of wireless communication with an electromagnetic reading module. The practical applicability of an eco-friendly battery-less epidermal thermometer, compatible with the UHF RFID standard, is here discussed by the help of experimentation with some volunteers. Comfortable reading procedures can be applied for both the operator and the patient. Experiments revealed a non negligible sensitivity of the temperature measurement versus the mutual distance between the reader and the sensor, that must be removed by a proper threshold filtering. Finally, the analysis of the sensor response for different placement position over the body, demonstrates that the axilla and chest loci provide only 0.6°C deviation from a reference tympanic measurement and are well accepted by the user which does not complain about the presence of the sensor.

Finger-Augmented RFID System to Restore Peripheral Thermal Feeling

V. Di Cecco, S. Amendola, P. P. Valentini, and G. Marrocco,  11th Annual IEEE International Conference on RFID, 9-11 May 2017, Phoenix, Az.

Finger-Augmented Devices (FAD) identify a particular wearable technology suitable to turn the human fingers into enhanced sensing surfaces for advanced human-computer interfaces. The feasibility of a full on-body UHF RFID-based FAD is here investigated for the first time. The system is aimed at providing impaired people suffering from a lack of thermal feeling, due to pathological disorders, with a realtime feedback of the temperature sensed by the fingertips. The considered RFID-FAD comprises an epidermal tag suitable to conformal application over the fingertip and an interrogation wrist patch antenna. The electromagnetic challenge concerns the possibility to establish a robust RFID link when both the reader antenna and the passive fingertip tag are attached onto the lossy human skin. The occurring near-field interaction is modeled by a two-port system and experimentally tested by means of a 3D hand mockup made by additive manufacturing. Simulations and measurement permitted to derive the upper-bound performance and to estimate the required power budget. The idea is finally demonstrated with a proof of concept in a realistic application.


Wireless Monitoring of Breath by means of a Graphene Oxide-based Radiofrequency Identification Wearable Sensor

M. C. Caccami, M. Y. S. Mulla, C. Di Natale and G. Marrocco,  11th European Conference on Antennas and Propagation, 19-24 March 2017, Paris, France.

The monitoring of the breathing dynamic charac- teristics, including the presence of biomarkers in exhaled breath, is of growing interest in noninvasive diagnosis of diseases. We describe a wearable radiofrequency identification (RFID) device hosting a flexible antenna suitable for integration into a facemask and a sensor made of graphene oxide sensitive to the humidity variations. The so obtained wearable wireless sensor was characterized in reference conditions and was then experimentally demonstrated to be capable of detecting the inhalation/exhalation cycles and abnormal patterns of respiration like the apnea by measuring the changes in graphene oxide resistance.


Optimal Performance of Epidermal Antennas for UHF Radio Frequency Identification and Sensing

S. Amendola and G. Marrocco,  IEEE Transactions on Antennas and Propagation, vol. 65, no. 2, pp. 473-481, February 2017.

Skin-mounted electronics is the new frontier for unobtrusive body-centric monitoring systems. In designing the wireless devices to be placed in direct contact with the human skin, the presence of the lossy body cannot be ignored because of strong electromagnetic interactions. In this paper, the performance of epidermal antennas, for application to radio frequency identification (RFID) links in the UHF band, was investigated by means of numerical simulations and laboratory tests on fabricated prototypes. The analysis demonstrates the existence of an optimal size of the antennas (from 3 to 6 cm for loops and from 6 to 15 cm for dipoles) and of upper bounds in the achievable radiation gain (less than −10 dB in the case of 0.5 mm thick application substrates) as a consequence of the balance between the two opposing mechanisms of radiation and loss. This behavior, which is controlled by the hosting medium, does not depend on the antenna shape, even if the loop layout permits considerably minimizing the device size. Even the conductivity of the antenna trace plays only a second-order role; low-cost inkjet printable paints with conductivity higher than  10^{4} S/m are suitable to provide radiation performance comparable with the performance of copper-made antennas. Starting from the investigation of the above cited physical phenomena, including the effect of common classes of suitable substrate membranes, guidelines are finally derived for the optimal design of real RFID epidermal antennas.


Design, Calibration and Experimentation of an Epidermal RFID Sensor for Remote Temperature Monitoring

S. Amendola, G. Bovesecchi, A. Palombi, P. Coppa, and G. Marrocco, IEEE Sensors Journal, vol. 16, no. 19, pp. 7250-7257, October 1, 2016.

An epidermal RFID sensor consists of a flexible antenna provided with a radiofrequency identification and sensing microchip directly stuck over the human skin by means of a submillimeter bio-compatible membrane. A compact-size epidermal RFID thermometer is here proposed and extensively experimented concerning its electromagnetic and thermal performance in case of battery-less and battery-assisted configurations. The antenna element embeds a mechanism for a post-manufacturing frequency retuning in order to adapt its response to the specific placement over the body. When attached over the skin the sensor is readable from up to 0.7 m in battery-less mode and 2.3 m in battery-assisted mode. A calibration procedure improved the accuracy of the IC sensor down to 0.18°C. The time constant evaluated by the first-order response of the IC to impulse heating (photo-flash) resulted in 4.3 s. The epidermal wireless thermometer was experimented in both supervised applications (manual reading) and in un-supervised architectures where users were continuously monitored by a fixed remote antenna or during the crossing of a surveillance gate. In all the considered cases, the reliability of the interrogation link was experimentally quantified and resulted robust for health monitoring applications in clinical and domestic settings and even for the automatic detection of anomalous temperature peaks of people walking within airports and at country border crossing.

Constrained Pole-Zero Synthesis of Phase-Oriented RFID Sensor Antennas

S. Caizzone, E. DiGiampaolo and G. Marrocco, IEEE Transactions on Antennas and Propagation, vol. 64, no. 2, pp. 496-503, Feb. 2016.

Passive sensing by means of radiofrequency identification has been extensively explored for various applications, such as gas detection, temperature change, and deformation. The sensing indicator is generally based on the amplitude and phase of the backscattered field. However, a degradation of the communication performance must be usually accepted for achieving the sensing capability. This work introduces a design method suitable for phase-based RFID sensors that permits to shape the phase response while preserving the impedance matching between the antenna and the microchip. The RFID sensor is modeled as a two-ports scatterer comprising a lumped sensor at one of the ports and an RFID chip at the other port. A pole-zero representation of the electromagnetic interaction between the reader and the RFID sensor allows to introduce a constrained design of the antenna with a full control on the sensor dynamic range and on the communication performance. The proposed method is numerically and experimentally validated by means of a pair of strongly coupled dipoles connected to a voltage-controlled varactor emulating a dynamic sensor response.

Precision and Accuracy in UHF-RFID Power Measurements for Passive Sensing

Occhiuzzi, C.; Marrocco, G., IEEE Sensors Journal, vol. 16, no. 9, pp. 3091-3098, 2016.

In spite of analog RFID sensors are gaining increasing attention from Academic and Industrial domains, their true applicability in the real world is still in question since it is not clear whether and in which conditions the variation of the measured signals related to the sensing activity may be distinguished from the measurement uncertainties. The RFID platform for analog sensing, namely with no dedicated sensing electronics, is here characterized in term of precision and accuracy with reference to the arrangement and the reproducibility of the setup. Numerical analysis and laboratory experimentations demonstrated that the precision of power metrics measurement is twice the resolution of low-cost readers and that the uncertainty on the distance and the alignment may play a major role on the data accuracy. The environment-independent indicator, like the Analog Identifier, revealed once again to be a very stable and robust metric. In overall, the obtained results suggest that analog RFID devices can be used as indicative sensing platform to identify a few levels of the phenomenon under observation. The sensing granularity can be improved by using low-power ICs while classification algorithms could be applied to increase the robustness of the detection.

Close Integration of a UHF-RFID Transponder into a Limb Prosthesis for Tracking and Sensing 

R. Lodato
and G. Marrocco, IEEE Sensors Journal, vol. 16, no. 6, March 2016.

The technology of structural radio systems that is well assessed in the avionic and naval communications is here applied to obtain antenna functionality out of a limb prosthesis with minimal changes to the device, in specific, an orthopedic nail. A microchip transponder based on the ultrahigh frequency- radio-frequency identification (RFID) communication standard is connected to the nail by means of a central notch forming a towel-bar-like antenna. The resulting device, called prosthetic structural tag, is such to preserve the mechanical continuity of the original nail, but it is also capable of energy harvesting and RFID. The electrical and geometrical control parameters for impedance tuning were identified using computer simulation and laboratory tests. The radiation performance is mostly dependent on the geometry of the notch, while it is rather unaffected by the length of the nail, so that the proposed layout may also be applied to different kinds of prosthesis. The experimented read distance at 870–960 MHz was more than 35-cm far from the limb surface. The augmented smart prosthesis is, hence, suitable to be monitored using an external non-contacting antenna for application to tracking and, in the near future, to monitor the prosthesis health status.

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Performance of Epidermal RFID Dual-loop Tag and On-skin Retuning

S. Amendola, S. Milici, G. Marrocco, IEEE Transactions on Antennas and Propagation, vol. 63, no. 8, August 2015

Originally introduced by the material science community, the epidermal electronics is now collecting interest also among antenna engineers for the potentiality to achieve thin and flexible sensing transponders that are suitable to application over the epidermis. Unlike conventional wearable antennas, which are generally decoupled by the lossy human body by means of spacers or shielding sheets, epidermal tags need to be placed at a very close touch with the skin thus providing poor communication capabilities. This paper investigates, by means of a detailed numerical and experimental study, the performance of an epidermal dual-loop tag for UHF radiofrequency identification (RFID) depending on the specific placement over different parts of the human body and for a variety of volunteers. An on-body tuning mechanism is also introduced and demonstrated in real applications at the purpose to improve the tag response and hence to enable the use of a same tag layout for all the UHF-RFID bands and for several placement loci.

S. Amendola, L. Bianchi, G. Marrocco, IEEE Antennas and Propagation Magazine, vol. 57, no. 3, pp. 23-37, June 2015

Movement detection of human body segments is a fertile research topic in Human-Computer interaction, as well as in medical and entertainment applications. In spite of most of the current methods to track motion are based on opto-electronic systems and wearable inertial sensors, promising solutions could spring from the application of the passive Radio Frequency Identification (RFID) technology. When the human body’s limbs move within an electromagnetic field radiated by an interrogating antenna, a movement-dependent modulation of the backscattered field is sensed by the remote receiver. The collected signals, pro- perly conditioned by wearable electromagnetic markers (tags), may therefore carry intrinsic information about the human motion. This paper investigates the potentiality of the synergy between Electromagnetics and Machine Learning technologies at the pur- pose to classify arms and legs gestures by using only passive and sensor-less transponders. The electromagnetic signals, backscatte- red from the tags during gestures, are collected by a fixed reader antenna and then processed by the Support Vector Machine (SVM) algorithm at the purpose to recognize both periodic limbs movements as well as to classify more complex random motion patterns. Experimental sessions demonstrated a classification accuracy higher than 80-90% that is fully comparable with that of more complex systems involving active wearable transceivers. The results further indicate that the achievable bit-rate is 48 bits/minute suggesting that the platform could be used to input coded controls to a gesture-oriented user interface.

Phase-oriented Sensing by means of Loaded UHF RFID Tags

Caccami M.C., Manzari S., Marrocco G., IEEE Transactions on Antennas and Propagation, vol. 63, no. 10, pp.4512-4520, October 2015

Radio Frequency Identification (RFID) tags are currently evolving from an augmented version of barcodes to passive and distributed sensors in the emerging Internet of Things. Most of the RFID sensing devices that have been experienced till now are based on power metrics. The change in the environment is converted into a variation of the antenna performance remotely sensed by a reader through a modulation of turn-on or backscattered power. This paper investigates a new sensing paradigm derived from the measurement of the phase of the electromagnetic signals that are backscattered from the tag in the UHF-RFID band. The main goal is to introduce a model of the phase response of antennas that are loaded by lumped sensitive materials. General properties, data-processing issues, the achievable dynamic ranges, sensitivities, and the measurement reproducibility of phase-oriented sensing are investigated by means of both numerical analysis and experimentations concerning an RFID humidity sensor as case study.

RFID & IoT: a Synergic Pair

S. Amendola, M. C. Caccami, A. Caponi, L. Catarinucci, V. Cardellini, E. Di Giampaolo, S. Manzari, F. Martinelli, S. Milici, C. Occhiuzzi, and G. Marrocco, IEEE RFID Virtual Journal, N.8, March 2015

Internet Of Things (IoT) is driven by a combination of sensors and actuators, connectivity, people and processes. The interactions among these entities are creating new types of applications and services.
IoT will provide a dynamic global network infrastructure with self-configuring capabilities where physical and virtual “Things” have both unique identities and physical attributes and are integrated into the information network in a fully transparent way for a final user. In the framework of Internet of things, an entity can be a farm animal with a biochip transponder for identification and tracking, an historical monument protected by a structural-health monitoring-network, a person with an implanted smart prosthesis, a car with built-in sensors or any other natural or man-made object which can be provided with an IP address and with the capability to exchange data over a network. So far, the Internet of Things has been mostly associated with machine-to-machine (M2M) communication in manufacturing and power, oil and gas utilities, but many other implementations are currently being investigated and even experimented.


Epidermal RFID Passive Sensor for Body Temperature Measurements

S. Milici, S. Amendola, A. Bianco and G. Marrocco, 2014 IEEE RFID Technology and Applications Conference (RFID-TA)

Real-time and continuous wireless measurement of human body temperature could enable a better control of many pathologies such as the wounds infection after surgery and the evolution of epidemics involving fever rush, as well as the monitor of athletic activities. This paper describes an RFID passive UHF epidermal sensor suitable to be directly attached onto the human skin by means of a bio-compatible transpiring Poli(
ε-caprolacton) (PCL) membrane. The antenna elements provide a broad matching band and even a post-fabrication tuning mechanism to better manage the specific placement over the body. The temperature is directly measured by the EM4325 microchip, also providing RFID communication capabilities. The epidermal sensor, that can be read up to 35 cm in case of 0.5 W EIRP emitted by the reader, has been moreover thermally calibrated versus a thermocouple and then applied to the measurement of human body temperature in both static and dynamic conditions with an accuracy of about 0.25°C with respect to reference measurements.

A Passive Temperature Radio-Sensor for Concrete Maturation Monitoring

S. Manzari, T. Musa, M. Randazzo, Z. Rinaldi, A. Meda and G. Marrocco, 2014 IEEE RFID Technology and Applications Conference (RFID-TA)

A planar “T” like passive UHF RFID temperature sensor is here proposed for application inside the fresh concrete at the purpose to hydration monitoring during the curing procedure into caissons. Since the concrete’s electromagnetic parameters significantly change along with the drying process, the antenna modeling and design consider both the electromagnetic and the chemical phenomena. The described tag layout is such to separate, by means of a two-conductor transmission line, the sensing device, e.g. a specialized RFID IC placed up to 15cm deep into the concrete, from the scavenging element, placed instead outside the concrete. Computer simulation and then extensive laboratory experimentation in real conditions demonstrated that, despite of the low sensitivity of the IC and the high losses of concrete, the proposed RFID sensor tag provides reasonable communication performance in passive mode with read ranges up to 2 meters, and fast and reliable temperature sensing capabilities that look comparable with that of more invasive and costly wired measurement systems.

Modeling and Applications of a Chemical-Loaded UHF RFID Sensing Antenna with Tuning Capability

S. Manzari, G. Marrocco, IEEE Trans. Antennas and Propagat., Vol. 62, N.1, pp 94-101, Jan. 2014

A key-issue of the wireless gas sensing by radio frequency identification is the capability to control the sensor's response while minimizing the amount of chemical interactive materials (CIM) required to dope the tag antenna. An open-circuit shielded slot-line layout is proposed as a general purpose tunable radio frequency identification (RFID) radiator, suitable to host small amounts of CIM. It operates both as a very efficient passive sensor and as a tool to estimate the electromagnetic equivalent parameters of the CIM during the gas exposure. A hybrid distributed-lumped model permits to separate the CIM's contribution from the antenna's response and, in addition, it provides a simple tool to shape the calibration curve relating RFID power signals to the physical changes of the environment. The tag layout and the method are applied to the UHF characterization of the conductive polymer Pedot:PSS and to the optimization of high-performance humidity sensor capable of a three-times higher sensitivity than those achieved by the current state of the art RFID devices.

C. Occhiuzzi, C. Vallese, S. Amendola, S. Manzari, G. MarroccoProcedia Computer Science, Vol.32, pp.190.197, 2014

An Ambient Intelligence platform, NIGHTCare, for remote monitoring and control of overnight living environment is here proposed. The platform, entirely based on RFID passive technology is able to recognize nocturnal behaviors and activities, generates automatic alarms in case of anomalous or pathological events and support diagnostics. The results of a complete test in real scenario are presented, together with a numerical assessment of electromagnetic safety issues.

Wireless Crack Monitoring by Stationary Phase Measurements from Coupled RFID Tags

S. Caizzone, E. DiGiampaolo, G. Marrocco, Trans. Antennas Propagat., Vol.62, N12, pp.6412-6419, Dec. 2014

The possibility to wirelessly monitor the state and the evolution of cracks is of increasing interest in emerging structural health monitoring systems. A simple and effective measurement method considers the placement of two passive radio frequency identification (RFID) antennas on top of the crack, so that the crack's evolution will produce a change of the inter-antenna coupling and in turn of the phase of the backscattered field. An ad-hoc design technique, based onto the coupled-modes physics, permits to maximize the sensor's sensitivity avoiding, or at least mitigating, the read range reduction during the evolution of the displacement that is instead typical of amplitude-oriented RFID displacement sensors. The proposed idea is demonstrated by numerical and experimental examples showing the possibility of sub-millimeter resolution with low-cost devices.

Sub-millimeter displacement sensing by Passive UHF RFID Antennas

C. Paggi, C. Occhiuzzi, G. Marrocco, IEEE Trans. Antennas and Propagat., Vol. 62, N.2, pp.905-912, Feb. 2014

A slotted patch is transformed into a wireless passive UHF-RFID sensor of uni-dimensional displacements by introducing a mechanic-electromagnetic modulation capable to convert sub-millimeter deformations into changes of the antenna’s response, remotely detectable. A design methodology allows to obtain the desired sensitivity and dynamic range in a fully controllable way. The sensor and the methodology are discussed through the help of preliminary laboratory experimentations on a concrete brick, showing the possibility to achieve resolutions better than 0.1 mm with low cost readers.

RFID Technology for IoT-based Personal Healthcare in SmartSpaces

S. Amendola, R. Lodato, S. Manzari, C. Occhiuzzi, G. Marrocco, IEEE Internet of Things Journal, Vol.1, N.2, pp. , 144.152, April 2014

The current evolution of the traditional medical model toward the participatory medicine can be boosted by the Internet of Things (IoT) paradigm involving sensors (environmental, wearable, and implanted) spread inside domestic environments with the purpose to monitor the user's health and activate remote assistance. RF identification (RFID) technology is now mature to provide part of the IoT physical layer for the personal healthcare in smart environments through low-cost, energy-autonomous, and disposable sensors. It is here presented a survey on the state-of-the-art of RFID for application to body centric systems and for gathering information (temperature, humidity, and other gases) about the user's living environment. Many available options are described up to the application level with some examples of RFID systems able to collect and process multichannel data about the human behavior in compliance with the power exposure and sanitary regulations. Open challenges and possible new research trends are finally discussed.

R. Lodato, V. Lopresto, G. Marrocco, R. Pinto, IEEE Transactions on Antennas and Propagation, Vol.62, No 10, Oct. 2014

Radio frequency identification (RFID) in the UHF band has been recently proposed as enabling technology to develop implanted radio-sensors to be integrated into orthopedic prosthesis because of the power autonomy and standardized communication protocols. This paper investigates the feasibility of direct and forward links for UHF-RFID (860-960 MHz) tags implanted into human limbs, that are interrogated by a noncontacting reader's antenna, with the purpose to label and, in a near future, to collect data about the health status of an implanted orthopedic prosthesis. Performance gain indicators of the through-the-body RFID channel are estimated by electromagnetic simulations over an anthropomorphic phantom as well as by means of experimentation with a real RFID communication link involving a simplified in vitro setup. The achieved results suggest that, by exploiting the current potentialities of RFID technology, and for the specific tag (loop antenna) and reader antenna (SPIFA) herein considered, a stable communication link with tags implanted inside limbs might be already feasible up to 10-35 cm from the body in full compliance with the constrains over electromagnetic exposure. In the particular case of implanted tag into an elbow, the estimated power margin in the direct and inverse links could be even suitable to set up sensing-oriented systems based onto turn-on and backscattered power modulation.

S. Manzari, A. Catini, G. Pomarico, C. Di Natale, G. Marrocco, IEEE Sensor Journal, Vol. 14, N.10, pp.3616-3623, 2014

Battery-less ultrahigh frequency (UHF) radio frequency identification (RFID) tags coated by proper sensitive layers have been recently demonstrated capable to play as low-cost sensors of some volatile compounds. The issue of cross-sensitivity and the possibility to develop an array of differently coated sensors are, however, still completely open. This paper investigates, through an experimental campaign involving a general-purpose sensor-antenna transducer, the potentiality of functionalized tags in the UHF RFID band to sense a multiplicity of volatile compounds, as well as the cross-sensitivity effects of different coatings in array configuration. Four effective materials, such as Pedot:PSS, doped PSS, SWCNT, and PDAC, revealed a remarkable sensitivity to ammonia, ethanol, octane, and water. Wireless sensing may be hence performed by narrowband processing of the power response of the RFID tags as well as by the broadband extraction of features related to the resonance shift. It was finally observed how the inter-antenna coupling may affect the sensor capability of an array of UHF tags in term of increased cross-sensitivity.


Constrained-Design of Passive UHF RFID Sensor Antennas

C. Occhiuzzi, G. Marrocco, IEEE Trans. Antennas and Propagat., Vol.61, N.6, pp.2972-2980, June 2013

Passive UHF RFID tags may be used, beside labeling, to remotely observe the physical/chemical change of the tagged object, through modulation of their impedance and gain, thus acting as sensor antennas. The design of this new class of devices can be mastered by fully understanding the relationship between communication and sensing with the purpose to balance the maximization of the dynamic range of the response with the stability of the read distance. A new kind of communication/sensing nomogram permits to display both behaviors in a unitary way and to predict their physical limits, as well as to formalize a multi-parameter general-purpose optimization methodology. The procedure is demonstrated by application to the design of a strain-gauge tag and of a level-detector wireless sensor.

Passive UHF RFID Antennas for Sensing Applications: Principles, Methods and Classifications

C. Occhiuzzi, S. Caizzone, G. Marrocco, IEEE Antennas and Propagat. Magaz., Vol.44, N.6, pp.14-34, Dec, 2013

UHF passive radio-frequency identification technology is rapidly evolving from simple labeling of things to wireless pervasive sensing. A remarkable number of scientific papers demonstrate that objects in principle can have their physical properties be remotely tracked and monitored all along their life cycle. The key background is a new paradigm of antenna design that merges together the conventional communication issues with more-specific requirements about sensitivity to time-varying boundary conditions. This paper presents a unified review of the state of the art of the tag-as-sensor problem. Particular care is taken to formalize the measurement indicators and the communication and sensing tradeoff, with the purpose to provide a first knowledge base for facing a large variety of emerging sensing applications.


Miniaturized wearable UHF-RFID tag with tuning capability

S. Manzari, S. Pettinari, G. Marrocco, Electronics Letters, VoL. 48, N. 21, p.1325–1326

By carving a ‘square-smile’ slot profile over a folded patch, a miniaturised UHF-RFID tag is obtained, having a convenient two-step tuning mechanism (coarse and fine). This is useful to adapt the same tag to European and US frequencies and to make on-site corrections. The antenna is half the size of a credit card and can be read up to 5m when attached onto the body. The flexible and lightweight EPDM foam substrate makes the tag suited to be integrated in badges, wallets, pockets, plasters, wristbands and various garments.

Performance Analysis of Pure Paraffin Wax as RFID tag Substrate

S. Manzari, A.A. Babar, L. Ukkonen, A. Z Elsherbeni, G. Marrocco, L.Sydanheimo, Microwave and Optical ans Technology Letters, vol.54, N.2, pp.442-446, Feb. 2012

The article presents an investigation of the performance of the Paraplast, a kind of pure paraffin wax, used as a substrate of RFID tag antennas operating at UHF RFID band. To achieve this purpose, two similar RFID tag antennas with same dimensions have been simulated, fabricated and tested. These include a simple dipole tag on a Rogers RT/Duroid 5880 substrate and on pure paraffin substrate. Because of the relatively close dielectric constant values, paraffin substrate is compared with Duroid RT5880. Paraffin wax can be considered as a low cost and low loss substrate. The main purpose in the future will be using paraffin as a passive temperature sensor, by exploiting the changes in molecular structure, volume and dielectric properties with temperature, especially near its melting point.

Feasibility of Body-centric Systems by Using passive textile RFID tags

S. Manzari, C, Occhiuzzi, G. Marrocco, IEEE Antennas and Propagation Magazine, Vol.54, N.9, pp 2851-2858, 2012

Recent progresses in the design of wearable RFID-tag antennas stimulate the idea of passive body-centric systems, wherein the required power to drive the wearable tags is directly scavenged from the interrogation signal emitted by the reader unit. While active body-centric links have been extensively investigated, the feasibility of passive systems is still questionable, due to the poor sensitivity of the tags and due to the modest reading distances. This paper describes a systematic measurement campaign involving low-profi le wearable textile tags in the UHF RFID band. It was demonstrated that both on-body and off-body links are affordable, with a power budget fully compliant with the available technology and the safety standards. The experiments permitted identifying the most-effi cient tag placements, and proposing some quantitative and general guidelines useful to characterize and design this kind of new system.

Design of Implanted RFID Tags for Passive Sensing of Human Body: the STENTag

C. Occhiuzzi, G. Contri, G. Marrocco, IEEE Trans. Antennas and Propagat. Vol.60, N.7, pp.3146-3154, 2012

Numerical processing of passive UHF-RFID tags' response may provide physical insight about the hosting object or about the nearby environment. This idea is here extended to implanted antennas with the purpose to sense the evolution of some human physiological and pathological process involving a local change of effective permittivity inside the body. The goal is to understand how master the design of this class of devices taking into account both communication and sensing capabilities. An ad hoc design methodology is here presented and discussed by means of a realistic medical case concerning the modification of an endo-vascular device to achieve a STENTag able to sense the state of the vessel wherein it has been implanted.

Humidity Sensing by Polymer-loaded UHF RFID Antennas

S. Manzari, C. Occhiuzzi, S. Nawale, A. Catini, C. Di Natale, and G. Marrocco, IEEE Sensors Journal, Vol.12, N.9, pp. 2851-2858, 2012

Passive ultra high-frequency radio frequency identification tags, besides item labeling, are also able to exploit capability to sense the physical state of the tagged object as well as of the surrounding environment. Here, a new family of polymer-doped tags are proposed and fully characterized for the detection of ambient humidity. A sensitive chemical species based on PEDOT:PSS is used to load a shaped slot, carved into a foldedlike patch tag. The communication and sensing capabilities of the resulting radio-sensor are investigated by means of simulation and measurements that show how to control and balance above opposite requirements by a proper deposition of the sensitive material. The device could have interesting applications in the assessment of the air quality within living and controlled rooms, in the monitoring of the conservation state of foods, in the preservation of walls, and even in the medical field, e.g., to monitor the healing of wounds.

Electromagnetic Models for Passive Tag to Tag Communications

G. Marrocco, S. Caizzone, IEEE Trans. Antennas and Propagat. Vol.60, N.11, pp. 5381-5389, 2012

The UHF passive radio frequency identification technology generally enables an asymmetric interaction between the reader and the tag, the latter only being able to respond to the query of the reader through backscattering modulation. Very recently, some experiments put into evidence the possibility to set up a tag-to-tag communication by using a simple illuminator. The key issues and the physical limitation of such a cross-link are here investigated both theoretically and numerically by fully accounting for the mutual coupling among the tags, their radiation properties and the impedance modulation. The analysis reveals that the cross-link range may be optimized by a proper design of the tags’ input impedance and that alignment of a multiplicity of tags could be able to communicate according to a simple routing strategy.


Passive Strain-Sensor based on Meander-line Antennas

C. Occhiuzzi, C. Paggi, G. Marrocco, IEEE Trans. Antennas and Propagat. Vol.59, N.12, pp.4836-4840, Dec. 2011

The processing of backscattered signals coming from RFID tags is potentially useful to detect the physical state of the tagged object. It is here shown how to design a completely passive UHF RFID sensor for strain monitoring starting from a flexible meander-line dipole whose shape factor and feed section are engineered to achieve the desired sensing resolution and dynamic range. This class of devices is low-cost, promises sub-millimeter resolution and may found interesting applications in the Structural Health Monitoring of damaged structures and vehicles as well as during extreme and adverse events.

RFID Passive Gas Sensor Integrating Carbon Nanotubes

C. Occhiuzzi, A. Rida, G. Marrocco, M. Tentzeris, IEEE Microwave Theory Tech. , Vol.59, N.10 part 2,, pp. 2674-2684, 2011

Carbon nanotube (CNT) composites are sensitive to the presence of gases due to their high surface-to-volume ratio and hollow structure that are well suited for gas molecule absorption and storage. Such sensing capability is here integrated with UHF RF identification (RFID) technology to achieve passive and low-cost sensors, remotely readable. CNT film (buckypaper) is used as a localized variable resistive load integrated into a tag antenna, which becomes able to transduce the presence of hazardous gas in the environment, ammonia in this case, into a change of its electromagnetic features. The dynamic range and the hysteresis of the radio sensor are investigated by simulations, equivalent circuits, and articulated experimentations within a true RFID link, providing the proof of concept and some guidelines for tag design.

RFID Grids: Part II - Experimentations

S. Caizzone, G. Marrocco, IEEE Trans. Antennas and Propagat. Vol. 59, N.8, pp. 2896-2904, Aug. 2011

The RFID Grid is a model for generally coupled multitudes of tags including single-chip tags in close mutual proximity or a single tag with a plurality of embedded microchips. Some properties of this new entity, useful for passive Sensing and for Security, are the possibility to increase the read-range and to provide responses rather insensitive to the interrogation modalities. These recently introduced issues are here experimented for the first time with many real-world examples comprising multi-chip configurations designed for improved power scavenging and for passive sensing of things.

Multi-chip RFID Antenna Integrating Shape Memory Alloys for Detection of Thermal Thresholds

S. Caizzone, C. Occhiuzzi, G. Marrocco, IEEE Trans. Antennas and Propagat. Vol.59, N.7, pp. 2488-2494, Jul, 2011

Low-cost wireless measurement of objects' temperature is one of the greatest expectation of radiofrequency identification technology for the so many applications in cold supply-chain control and safety assessment in general. In this context, the paper proposes a dual-chip UHF tag embedding shape memory alloys (SMA) able to transform the variation of the tagged item's temperature into a permanent change of antenna radiation features. This event-driven antenna is hence able to selectively activate the embedded microchips according to the temperature above or below a given threshold. A general design methodology for the resulting two-ports tag antenna is here introduced and then applied to prototypes able to work at low (around 0°C) and high (80°C) temperatures.

RFID Grids: Part I - Electromagnetic Theory

G. Marrocco, IEEE Trans. Antennas and Propagat. Vol.59, N.3, pp. 1019-1026, March 2011

The close displacement of UHF RFID tags can be considered as an electromagnetic interconnected system having specific properties. The so denoted RFID Grid includes single-chip tags in close mutual proximity or a single tag with a multiplicity of embedded microchips. A multi-port scattering framework is used to derive the macroscopic parameters governing the system response which could be optimized for the specific application. Moreover, unique features are introduced, such as the possibility to improve the power scavenging and the generation of analog identifiers and fingerprint. The last ones are electromagnetic responses independent on the position and orientation of the reader and on the nearby environment, with great relevance for Sensing and Security.


Pervasive Electromagnetics: sensing paradigms by passive RFID Technology

G. Marrocco, IEEE Wireless Communications, Invited Paper, Vol.17, N.6, pp.10-17, Dec. 2010

Things equipped with electronic labels having both identification and sensing capability could naturally be turned into digital entities in the framework of the Internet of Things. Radio frequency identification (RFID) technology offers the natural background to achieve such functionalities, provided that the basic physics governing the sensing and electromagnetic interaction phenomena are fully exploited. The sensing of Things is here reviewed from an electromagnetic perspective with the purpose of showing how advanced performance may be achieved by means of low-cost batteryless devices. A possible classification of basic sensing modalities is introduced, and many ideas, at different stages of maturity, are then discussed with the help of examples ranging from the sensing of non-living Things up to the more challenging sensing of Humans.

The RFID Technology for Neuroscience: feasibility of Limbs' Monitoring in Sleep Diseases

C. Occhiuzzi, G. Marrocco, IEEE Trans. Information Technology in Biomedicine, Vol.14, N.1, pp. 37-43, Jan. 2010

This contribution investigates the feasibility of the passive UHF RF identification technology for the wireless monitoring of human bodymovements in some common sleep disorders by means of passive tags equipped with inertial switches. Electromagnetic and mechanical models as well as preliminary experimentations are introduced to analyze all the significant issues concerning the required power, the tag antenna design, the read distance, and the expected biosignals collected by the interrogation device.

Hermite-Rodriguez UWB Circular Arrays

G. Marrocco, G. Galletta, IEEE Trans. Antennas and Propagat., Vol.58, N.2, pp.381-390, Feb. 2010

Pulsed circular arrays are collecting growing interest in radar applications such as automotives and indoor navigations. This contribution presents the analytic derivation of the spacetime and energy patterns of pulsed circular arrays in terms of geometrical and electrical parameters as well as of the signal distortion produced by the antennas’ response. It is shown that the field emitted by circular arrays with many elements can be represented as a summation of a practically finite set of high-order Hermite-Rodriguez waveforms, while the energy pattern is a generalized Hypergeometric Function. The angular and temporal resolutions are finally related, through handy formulas, to the array size, the input signals and to the antenna types.

Modeling design and experimentation of wearable UHF RFID sensor tag antennas

C. Occhiuzzi, S. Cippitelli, G. Marrocco, IEEE Trans. Antenna Propagat., Vol.58 N.8, pp. 2490 - 2498, 2010

Design of effective wearable tags for UHF RFID applications involving persons is still an open challenge due to the strong interaction of the antenna with the human body which is responsible of impedance detuning and efficiency degradation. A new tag geometry combining folded conductors and tuning slots is here discussed through numerical analysis and extensive experimentation also including the integration of a passive motion detector. The achieved designs, having size comparable with a credit card, may be applied to any part of the body. The measured performance indicates a possible application of these body-worn tags for the continuous tracking of human movements in a conventional room.

RFID-Network Planning by Particle Swarm Optimization

E. Di Giampaolo, F. Fornì, G. Marrocco, Aces Journal, Vol.25, N.3, pp. 263-272, March 2010

The design of an ad-hoc network of readers for a complex RFID system in large areas requires the deployment of a large number of readers due to the limited range of reader-tag communication. For passive tags the factors affecting the performance of the reader-tag communication depends on many physical and geometrical parameters. Line of sight is a constraint of the reader-tag link while scattering objects producing electromagnetic interferences affect the shape and the extension of the read-zone i.e. the region where a reader can activate a tag. This region depends not only on the emitted power and reader/tag antennas radiation patterns but also on the propagation environment. When a number of readers are planned in a network, mutual coverage of read-zones and mutual interference among readers are undesired while safety regulation constraints have to be fulfilled in the whole area. Simple and effective models of electromagnetic elements involved in the planning are developed and included in the frame of a Particle Swarm Optimization algorithm. Numerical results show the effectiveness of the method.


Estimation of UHF RFID Reading Regions in Real Environments

E. Di Giampaolo, R. Aliberti, G. Marrocco, IEEE Antennas and Propagation Magazine, Vol.51, N.6, pp. 44-57, Dec. 2009

The reading range is one of the most critical performance indicators of radio-frequency identification (RFID) systems. It depends on many physical and geometrical parameters. Typically, in the ultra-high-frequency band (UHF: 860 MHz to 960 MHz), the maximum size of the reading region is estimated by the free-space propagation model. This is based on the Friis formula, even if much more accurate predictions may be accomplished nowadays by time-consuming electromagnetic simulations, accounting for the antennas and the interaction with the nearby environment. This paper proposes a general parameterization of the three-dimensional reading region. This done having introduced all of the accessible system data, such as the emitted power, the reader and tag-over-object radiation patterns, and also the interrogation duty cycle, the scenario features, and the safety regulation constraints. Within this framework, the opportunity and some improvements of the free-space model are analyzed. They are compared with measurements and with more-accurate three-dimensional simulations of realistic environments. The discussion demonstrates the validity range of the free-space approximations, and evaluates the improvement achieved by including the main interactions with the environment. The derived formulas are ready to use and to be applied for the planning and optimization of reader-tag networks.


G. Marrocco, IEEE Antennas and Propagation Magazine, Vol.50, N.3 pp.147-150, June 2008

Multi-port Sensor RFIDs for Wireless Passive Sensing - Basic Theory and Early Simulations

G. Marrocco, L. Mattioni, C. Calabrese, IEEE Trans. Antennas Propagation. Vol.56, N.8, pp., Aug. 2008

A new family of passive sensor radio-frequency identification devices is here proposed for applications in the context of wireless sensor networks. The new tags, working in the ultra-high frequency band, are able to detect the value or the change of some features of the tagged body without using any specific sensor. Such tags are provided with multiple chips embedded either within a cluster of cooperating antennas or in a single multiport antenna, and exploit the natural mismatch of the antenna input impedance caused by the change of the tagged object. A basic theory of multiport sensor tags is formulated with the purpose to describe the possible classification and detection performances in a unitary context. Some numerical examples and a first experiment corroborate the feasibility of the idea.

Meandered-slot antennas for sensor-RFID tags

G. Marrocco, C. Calabrese, IEEE Antennas and Wireless Propagation Letters. Vol.7, pp.5-8, 2008

This letter introduces a planar antenna layout suited to Sensor-RFID fabrication. The geometry is based on a meandered-slot profile on a suspended patch and permits to host sensors and electronics in a small space. The available geometrical parameters are optimized by means of a Genetic Algorithm (GA) procedure aimed to maximize the antenna realized gain. The antenna performances are discussed through examples and prototypes.

The Art of UHF RFID Antenna Design: Impedance Matching and Size Reduction Techniques

G. Marrocco, IEEE Antennas and Propagation Magazine, Vol.50, N.1, pp.66-79, Feb. 2008

Radio-frequency identification technology, based on the reader/tag paradigm, is quickly permeating several aspects of everyday life. The electromagnetic research mainly concerns the design of tag antennas having high efficiency and small size, and suited to complex impedance matching to the embedded electronics. Starting from the available but fragmented open literature, this paper presents a homogeneous survey of relevant methodologies for the design of UHF passive tag antennas. Particular care is taken to illustrate, within a common framework, the basic concepts of the most-used design layouts. The design techniques are illustrated by means of many noncommercial examples.

Naval Structural Antenna Systems for Broadband HF Communications - Part III: Experimental Evaluation on Scaled Prototypes

L. Mattioni, F. Di Lanzo, G. Marrocco, IEEE Trans. Antennas Propagation, vol.56, n.7, pp.1882-1887, Jul. 2008

We describe the design, fabrication and measurement of reduced-size prototypes of the naval structural antenna, recently proposed as a compact and multifunction solution to broadband naval communications. The original broadband HF sub-radiator, loaded by lumped impedances, is scaled down to the VHF/UHF ranges and re-designed in planar technology in order to simplify and to automate the fabrication process. Measurement on single-port and 4-port antennas, in which the central structure resembles a naval funnel and a big mast, have shown a good agreement with the simulations.

Time Domain Synthesis of Pulsed Arrays

M. Ciattaglia, G. Marrocco, IEEE Trans. Antennas Propagation, Vol.56, N.7, pp.1928-1938, Jul. 2008

Pulsed arrays are becoming popular in new ultrawideband applications to enhance the robustness of transmitted and received signals in complex environments and to identify the angle of arrival of multiple echoes. A global synthesis technique is here proposed to shape the array field in accordance to given angle-time constraints. The synthesis problem is cast as the inverse Radon transform of a desired array mask, applying the alternate projections method to include constraints over the input signals’ waveform and to improve the synthesis robustness. The unknown array currents are generated as linear combinations of Hermite–Rodriguez functions in order to achieve a simple and realizable beamforming network. The effectiveness of the method is demonstrated by many examples.


RFID antennas for the UHF remote monitoring of human subjects

G. Marrocco, IEEE Trans. Antennas Propagat., Vol.55, N.6, pp. 1862-1870, June 2007

This paper addresses the design of passive and semi- passive transponder antennas for radio frequency identification applications involving the human body as the object to be tagged or bio-monitored. A planar tag antenna geometry, that is based on a suspended patch fed via a nested slot and is able to host sensors and electronics, is here introduced. Guidelines for conjugate impedance matching are given for different kinds of microchip transmitters, within power limitations as well as space constraints. Finally, the antenna matching performance is experimentally evaluated utilizing a body-tissue phantom.

Simultaneous time-frequency modeling of ultra-wideband antennas by two-dimensional Hermite processing

G. Marrocco, M. Migliorelli, M. Ciattaglia, Progress In Electromagnetic Research, PIER, Vol. 68, pp. 317-337, 2007

This paper proposes an approximate space-time-frequency field representation for directive Ultra-wideband antennas useful to be introduced into a system-level evaluation tool. Based on the observation that the very near field collected on a plane close to the antenna exhibits a compact support, such a field is processed in the time domain by the two-dimensional Hermite transform. This approach permits to simultaneously express the antenna impulse response and the transfer function by semi-analytical formulas. The theory is demonstrated by numerical examples which highlights that good representations of complex antennas can be achieved by a small set of associate Hermite functions.

Design of a Broad-band HF Antenna for Multi-mode Naval Communications - part II: extension to VHF/UHF ranges

L. Mattioni, G. Marrocco, IEEE Antennas and Wireless Propagation Letters, Vol.2, pp.83-85, 2007

This letter proposes a broadband antenna system with omnidirectional features, operating from 2 to 440 MHz. The basic antenna structure is the bifolded monopole, recently proposed as multimode high-frequency (HF) naval antenna, which is here augmented with a top-mounted discone mainly operating in the very-high-frequency (VHF) band. A mechanical and electrical integration strategy, which can be also extended to other antenna typologies, based on the lumped impedance loading to reduce the interantenna coupling, is described.


BLADE: A Broadband Loaded Antennas DEsigner

L. Mattioni, G. Marrocco, IEEE Antennas Propagat.Magazine, Vol. 48, N.5, pp.120 - 129, 2006

This paper presents a software tool for designing loaded antennas equipped with matching networks for broadband or multiband applications. The software implements a genetic algorithm to automatically optimize the large set of parameters involved in the design procedure. The graphical interface has been designed in MATLAB® to be used together with the popular NEC solver. However, the possibility of handling reduced-port models of the antenna permits the use of any kind of numerical solver for the electromagnetic analysis. Some examples of broadband and multi-band antenna designs in a complex environment demonstrate the potential of the tool.

Investigation on antenna coupling in Pulsed Arrays

M. Ciattaglia, G. Marrocco, IEEE Trans. Antennas Propagat. vol. 54, n.3, pp.835-843, March, 2006

Pulsed arrays are becoming popular in new ultrawide-band applications to achieve long-range coverage, high capacity and to identify the angle of arrival of multiple echoes in complex environments. As in the monochromatic regime, distortion of ultrawide-band transmitted and received signals can result from the coupling between individual radiators that are in close proximity. This paper investigates the time-domain coupling in finite arrays that radiate short pulses, by introducing the concept of time-domain "active" array factor and "active" element factor. The proposed model highlights the signal-distortion phenomenology and obtains useful guidelines to reduce pulse coupling, even in dense arrays, by a proper choice of the geometrical and electrical parameters.

Naval Structural Antenna Systems for Broadband HF Communications - Part II: Design Methodology for Real Naval Platforms

G. Marrocco, L. Mattioni, V. Martorelli, IEEE Trans. Antennas Propagat. vol. 54, n.11, pp.3330 - 3337, Nov., 2006

Recently, it was shown how to make a multipurpose broadband HF antenna system out of existing naval superstructures such as the funnel or a big mast. The idea was discussed by means of canonical structures, e.g., a cylindrical body of circular or square cross-section, placed onto an infinite ground plane. This paper investigates the critical aspects concerning the extension of naval structural antenna concept to real ship platforms with the aim to define a general design methodology for impedance matching and radiation pattern control. The method is described with reference to a realistic frigate model, whose big mast is transformed into a broadband HF antenna system able to perform communications by both sea-wave and sky-wave links.