Spatial Identification Methods and Systems for RFID Tags

Disertační práce je zaměřena na metody a systémy pro měření vzdálenosti a lokalizaci RFID tagů pracujících v pásmu UHF. Úvod je věnován popisu současného stavu vědeckého poznání v oblasti RFID prostorové identifikace a stručnému shrnutí problematiky modelování a návrhu prototypů těchto systémů. Po specifikaci cílů disertace pokračuje práce popisem teorie modelování degenerovaného kanálu pro RFID komunikaci. Detailně jsou rozebrány metody měření vzdálenosti a odhadu směru příchodu signálu založené na zpracování fázové informace. Pro účely lokalizace je navrženo několik scénářů rozmístění antén. Modely degenerovaného kanálu jsou simulovány v systému MATLAB. Významná část této práce je věnována konceptu softwarově definovaného rádia (SDR) a specifikům jeho adaptace na UHF RFID, která využití běžných SDR systémů značně omezují. Diskutována je zejména problematika průniku nosné vysílače do přijímací cesty a požadavky na signál lokálního oscilátoru používaný pro směšování. Prezentovány jsou tři vyvinuté prototypy: experimentální dotazovač EXIN-1, měřicí systém založený na platformě Ettus USRP a anténní přepínací matice pro emulaci SIMO systému. Závěrečná část je zaměřena na testování a zhodnocení popisovaných lokalizačních technik, založených na měření komplexní přenosové funkce RFID kanálu. Popisuje úzkopásmové/širokopásmové měření vzdálenosti a metody odhadu směru signálu. Oba navržené scénáře rozmístění antén jsou v závěru ověřeny lokalizačním měřením v reálných podmínkách.The doctoral thesis is focused on methods and systems for ranging and localization of RFID tags operating in the UHF band. It begins with a description of the state of the art in the field of RFID positioning with short extension to the area of modeling and prototyping of such systems. After a brief specification of dissertation objectives, the thesis overviews the theory of degenerate channel modeling for RFID communication. Details are given about phase-based ranging and direction of arrival finding methods. Several antenna placement scenarios are proposed for localization purposes. The degenerate channel models are simulated in MATLAB. A significant part of the thesis is devoted to software defined radio (SDR) concept and its adaptation for UHF RFID operation, as it has its specialties which make the usage of standard SDR test equipment very disputable. Transmit carrier leakage into receiver path and requirements on local oscillator signals for mixing are discussed. The development of three experimental prototypes is also presented there: experimental interrogator EXIN-1, measurement system based on Ettus USRP platform, and antenna switching matrix for an emulation of SIMO system. The final part is focused on testing and evaluation of described positioning techniques based on complex backscatter channel transfer function measurement. Both narrowband/wideband ranging and direction of arrival methods are validated. Finally, both proposed antenna placement scenarios are evaluated with real-world measurements.

Design of a Wideband Inductively Coupled Loop Feed Patch Antenna for UHF RFID Tag

A planar wideband patch antenna for ultra-high frequency (UHF) radio frequency identification (RFID) tag for metallic applications is presented in this research work. Three different shape patches are inductively coupled to a triangle loop to form wide impedance bandwidth for universal application UHF (860-960 MHz) RFID. The structure of proposed antenna exhibits planar profile to provide ease of fabrication for cost reduction well suited for mass production. The simulation of the antenna was carried out using Finite Element Method (FEM) based software, Ansoft HFSS v13. The simulated and measured impedance bandwidth of 113 MHz and 117 MHz (Return Loss≥6 dB) were achieved to cover the entire UHF RFID operating frequency band worldwide. The simulated and measured radiation patterns at the operating frequency of 915 MHz are in good agreement. Moreover the simulated minimum antenna gain at the bore sight direction in free space and when mounted on 200 x 200 mm2 metal plate are -15 dBi and -14dBi respectively which is enough to provide reasonable read range over the entire UHF RFID system operating band

Exploitation of Transparent Conductive Oxides in the Implementation of a Window-Integrated Wireless Sensor Node

Exploitation of transparent conductive oxides (TCO) to implement an energy-autonomous sensor node for a wireless sensor network (WSN) is studied and a practical solution presented. In the practical implementations, flexible and rigid substrates that is polyimide and glass, are coated with TCO, namely aluminum doped zinc oxide (AZO). AZO-coated flexible substrates are used to form thermoelectric generators (TEG) that produce electricity for the sensor electronics of the node from thermal gradients on a window. As the second solution to utilize AZO, its conductive properties are exploited to implement transparent antennas for the sensor node. Antennas for a UHF RFID transponder and the Bluetooth radio of the node are implemented. A prototype of a flexible transparent TEG, with the area of 67 cm2 when folded, was measured to produce power of 1.6 uW with a temperature difference of 43 K. A radiation efficiency of -9.1 dB was measured for the transparent RFID antenna prototype with the center frequency of 900 MHz. Radiation efficiencies between -3.8 dB and -0.4 dB, depending on the substrate, were obtained for the 2.45 GHz Bluetooth antenna.Comment: 10 pages, 14 figures, last author version accepted for publication in IEEE Sensors Journa

Skin-Mounted RFID Sensing Tattoos for Assistive Technologies

UHF RFID technology is presented that can facilitate new passive assistive technologies. Tongue control for human computer interfaces is first discussed where a tag is attached to the hard palate of the mouth and the tag turn-on power is observed to vary in response to tongue proximity. Secondly, a stretchable tag is fabricated from Lycra fabric that contains conducting silver fibres. The application of strain to the elastic tag again causes the required power at the reader to activate the tag to vary in proportion. This elastic tag is proposed as a temporary skin mounted strain gauge that could detect muscle twitch in the face or neck of an otherwise physically incapacitated person. Either design might be applied to the steering function of a powered wheelchair, or to facilitate the control of a computer mouse. Better than 3dB isolation is achieved in the tongue switching case and approximately 0.25dBm per percentage stretch is observed for the strain gauge

ISI Cancellation Using Blind Equalizer Based on DBC Model for MIMO-RFID Reader Reception

Under the dyadic backscatter channel (DBC) model, a conventional zero forcing (ZF) and minimum mean square error (MMSE) method for MIMO-RFID reader reception are not able to be rapidly cancelled inter-symbol interference (ISI) because of the error of postpreamble transmission. In order to achieve the ISI cancellation, the conventional method of ZF and MMSE are proposed to resolve a convergence rate without postpreamble by using a constant modulus algorithm (CMA). Depending on the cost function, the CMA is used which based on second order statistics to estimate the channel statement of channel transfer function. Furthermore, the multiple-tag detection is also considered under the assumption of the maximum likelihood estimation. The comparison of the conventional method and the proposed method is analyzed by using computer simulation and experimental data. We can see that the proposed method is better than the conventional method with a faster ISI cancelling and a lower bit error rate (BER) improving as up to 12 tags

Electromagnetic Assessment of UHF-RFID Devices in Healthcare Environment

In this work, the evaluation of electromagnetic effect of Ultra High Frequency Radio Frequency Identification (UHF-RFID) passive tags used in the healthcare environment is presented. In order to evaluate exposure levels caused by EM field (865–868 MHz) of UHF-RFID readers, EM measurements in an anechoic chamber and in a real medical environment (Hospital Universitario de Canarias), as well as simulations by 3D Ray Launching algorithm, and of biophysical exposure effects in human models are presented. The results obtained show that the EM exposure is localized, in close vicinity of RFID reader and inversely proportional to its reading range. The EM exposure levels detected are sufficient to cause EM immunity effects in electronic devices (malfunctions in medical equipment or implants). Moreover, more than negligible direct effects in humans (exceeding relevant SAR values) were found only next to the reader, up to approximately 30% of the reading range. As a consequence, the EM risk could be firstly evaluated based on RFID parameters, but should include an in situ exposure assessment. It requires attention and additional studies, as increased applications of monitoring systems are observed in the healthcare sector—specifically when any system is located close to the workplace that is permanently occupied.This work was supported by Instituto de Salud Carlos III project “Electromagnetic “Characterization in Smart Environments of Healthcare, and their involvement in Personal, Occupational, and Environmental Health” (PI14CIII/00056) https://portalfis.isciii.es/es/Paginas/DetalleProyecto. aspx?idProyecto=PI14CIII%2f00056 (accessed on 24 July 2022), and project “ (PI19CIII/00033) TMPY 508/19 “ Metrics development for electromagnetic safety assessment in healthcare centers in the context of 5G“ https://portalfis.isciii.es/es/Paginas/DetalleProyecto.aspx?idProyecto=PI19 CIII%2f00033, (accessed on 24 July 2022) from Sub-Directorate-General for Research Assessment and Promotion. The results of a research task (II.PB.15) carried out within the National Programme “Improvement of safety and working conditions” partly supported in Poland in 2020-2022-within the scope of research and development-by the National Centre for Research and Development were also included.S

Electromagnetic assessment of UHF-RFID devices in healthcare environment

In this work, the evaluation of electromagnetic effect of Ultra High Frequency Radio Frequency Identification (UHF-RFID) passive tags used in the healthcare environment is presented. In order to evaluate exposure levels caused by EM field (865–868 MHz) of UHF-RFID readers, EM measurements in an anechoic chamber and in a real medical environment (Hospital Universitario de Canarias), as well as simulations by 3D Ray Launching algorithm, and of biophysical exposure effects in human models are presented. The results obtained show that the EM exposure is localized, in close vicinity of RFID reader and inversely proportional to its reading range. The EM exposure levels detected are sufficient to cause EM immunity effects in electronic devices (malfunctions in medical equipment or implants). Moreover, more than negligible direct effects in humans (exceeding relevant SAR values) were found only next to the reader, up to approximately 30% of the reading range. As a consequence, the EM risk could be firstly evaluated based on RFID parameters, but should include an in situ exposure assessment. It requires attention and additional studies, as increased applications of monitoring systems are observed in the healthcare sector—specifically when any system is located close to the workplace that is permanently occupied.This work was supported by Instituto de Salud Carlos III project “Electromagnetic Characterization in Smart Environments of Healthcare, and their involvement in Personal, Occupational, and Environmental Health” (PI14CIII/00056), and project (PI19CIII/00033) TMPY 508/19 “Metrics development for electromagnetic safety assessment in healthcare centers in the context of 5G“ from Sub-Directorate-General for Research Assessment and Promotion. The results of a research task (II.PB.15) carried out within the National Programme “Improvement of safety and working conditions” partly supported in Poland in 2020–2022—within the scope of research and development—by the National Centre for Research and Development were also included