A Passive UHF RFID System over Ethernet Cable for Long Range Detection

This paper proposes a new form of passive UHF RFID system which has high tag detection accuracy but lower costs than existing systems for wide-range RFID scenarios requiring greater flexibility. This new system concept consists of a central baseband controller and a remote antenna subsystem, connected using a twisted-pair cable. Baseband signals are transmitted over the twisted-pair cable during the inventory session, and the transmitted radio frequency (RF) signals are up and down converted in the antenna subsystem. – 88 dBm reader sensitivity is achieved with an active leakage cancellation block, showing little degradation in tag detection performance over a 300m of Cat5e cable between the controller and the antenna. An average leakage suppression of 36.9 dB can be achieved with a fixed transmission power of 26.5 dBm. Compared with conventional RFID systems using coaxial cables between the reader and antenna, the presented system is superior in terms of link distance, link cost, and installation flexibility

A Novel Long-Range Passive UHF RFID System over Twisted-pair Cable

Radio Frequency Identification (RFID) is one of the most representative, rapidly growing, and highly extendable technologies, which uses electromagnetic waves in accordance with specific communications standards and regulations to identify, track, or even localise desired objects. However, due to its high cost, limited read range, and uncertain reliability, its adoption still lags, especially in large-scale organisations. Even though an RFID distributed antenna system (DAS) can greatly improve the detection range and read rate of a single reader when system uses different combinations of antenna states with frequency and phase hopping, the lossy and heavy coaxial cables between reader and antennas still limits the system coverage and design flexibility for wide-area passive UHF RFID applications. In order to develop a cost-efficient and flexibly-installed passive RFID DAS, a novel large-range passive UHF RFID system over twisted-pair cable is proposed in this dissertation. This new system consists of one baseband central controller and one antenna subsystem, connected by a commonly used twisted-pair cable. It is shown that transmitting/receiving low frequency baseband signals over a twisted-pair cable can significantly reduce cable attenuation and extend the communication distance. A simulation is conducted to demonstrate that frequency and phase hopping can also be remotely controlled to fit this system structure by slightly varying the frequency or phase of the input reference signal of the frequency synthesis system. The features of twisted-pair cable in terms of its low cost, light weight, and bend radius greatly improve the design and installation flexibility of an RFID system. The implemented system is designed based on the ISO 18000-6C and EPC Class 1 Generation 2 standards, and can operate according to FCC (902-928 MHz) and ETSI (865-868MHz) regulations. The results of the measurement show the reader can achieve a sensitivity of - 94.5 dBm over 30 m Cat5e cable, and its sensitivity can still remain at around -94.2 dBm over 150 m Cat5e cable. The experimental results of tag detection show that the passive tags can be successfully detected over a 6 m wireless range following a 300 m of twisted-pair cable between the central controller and antenna. This detection range cannot be achieved by existing commercial RFID systems. Since the transmission and reception in a RFID system are simultaneous, finite isolation of the circulator/directional coupler and environmentally dependent reflection ratio of the antenna lead to serious leakage problems. Leakage can directly cause sensitivity degradation due to saturation of the RF components. A fast leakage suppression block is developed in efforts to solve this problem. Measurements show that this new canceller can deliver an average suppression of 36.9 dB, and this excellent performance remains when the system uses frequency hopping. With help of an improved scanning algorithm, this canceller can find its optimal status within 38 ms, and this settling time is short enough for most commercial RFID readers. By reducing the number of voltage samples taken, the convergence time can be further improved. To fully investigate this new passive UHF RFID system value, a comparison study between the new system and a commercial system is conducted. This new automatic passive UHF RFID system is confirmed to deliver high performance long-range passive tag detection. Particular advantages are shown in the fast tag read rate and capability of uplink SNR improvement. This novel system is also superior to conventional RFID systems in terms of link distance, link cost, and installation flexibility

Sistemas eficientes de transmissão de energia sem-fios e identificação por radiofrequência

Doutoramento em Engenharia EletrotécnicaIn the IoT context, where billions of connected objects are expected to be ubiquitously deployed worldwide, the frequent battery maintenance of ubiquitous wireless nodes is undesirable or even impossible. In these scenarios, passive-backscatter radios will certainly play a crucial role due to their low cost, low complexity and battery-free operation. However, as passive-backscatter devices are chiefly limited by the WPT link, its efficiency optimization has been a major research concern over the years, gaining even more emphasis in the IoT context. Wireless power transfer has traditionally been carried out using CW signals, and the efficiency improvement has commonly been achieved through circuit design optimization. This thesis explores a fundamentally different approach, in which the optimization is focused on the powering waveforms, rather than the circuits. It is demonstrated through theoretical analysis, simulations and measurements that, given their greater ability to overcome the built-in voltage of rectifying devices, high PAPR multi-sine (MS) signals are capable of more efficiently exciting energy harvesting circuits when compared to CWs. By using optimal MS signals to excite rectifying devices, remarkable RF-DC conversion efficiency gains of up to 15 dB with respect to CW signals were obtained. In order to show the effectiveness of this approach to improve the communication range of passive-backscatter systems, a MS front-end was integrated in a commercial RFID reader and a significant range extension of 25% was observed. Furthermore, a software-defined radio RFID reader, compliant with ISO18000-6C standard and with MS capability, was constructed from scratch. By interrogating passive RFID transponders with MS waveforms, a transponder sensitivity improvement higher than 3 dB was obtained for optimal MS signals. Since the amplification and transmission of high PAPR signals is critical, this work also proposes efficient MS transmitting architectures based on space power combining techniques. This thesis also addresses other not less important issues, namely self-jamming in passive RFID readers, which is the second limiting factor of passive-backscatter systems. A suitable self-jamming suppression scheme was first used for CW signals and then extended to MS signals, yielding a CW isolation up to 50 dB and a MS isolation up 60 dB. Finally, a battery-less remote control system was developed and integrated in a commercial TV device with the purpose of demonstrating a practical application of wireless power transfer and passive-backscatter concepts. This allowed battery-free control of four basic functionalities of the TV (CH+,CH-,VOL+,VOL-).No contexto da internet das coisas (IoT), onde são esperados bilhões de objetos conectados espalhados pelo planeta de forma ubíqua, torna-se impraticável uma frequente manutenção e troca de baterias dos dispositivos sem fios ubíquos. Nestes cenários, os sistemas radio backscatter passivos terão um papel preponderante dado o seu baixo custo, baixa complexidade e não necessidade de baterias nos nós móveis. Uma vez que a transmissão de energia sem fios é o principal aspeto limitativo nestes sistemas, a sua otimização tem sido um tema central de investigação, ganhando ainda mais ênfase no contexto IoT. Tradicionalmente, a transferência de energia sem-fios é feita através de sinais CW e a maximização da eficiência é conseguida através da otimização dos circuitos recetores. Neste trabalho explora-se uma abordagem fundamentalmente diferente, em que a otimização foca-se nas formas de onda em vez dos circuitos. Demonstra-se, teoricamente e através de simulações e medidas que, devido à sua maior capacidade em superar a barreira de potencial intrínseca dos dispositivos retificadores, os sinais multi-seno (MS) de elevado PAPR são capazes de excitar os circuitos de colheita de energia de forma mais eficiente quando comparados com o sinal CW tradicional. Usando sinais MS ótimos em circuitos retificadores, foram verificadas experimentalmente melhorias de eficiência de conversão RF-DC notáveis de até 15 dB relativamente ao sinal CW. A fim de mostrar a eficácia desta abordagem na melhoria da distância de comunicação de sistemas backscatter passivos, integrou-se um front-end MS num leitor RFID comercial e observou-se um aumento significativo de 25% na distância de leitura. Além disso, desenvolveu-se de raiz um leitor RFID baseado em software rádio, compatível com o protocolo ISO18000-6C e capaz de gerar sinais MS, com os quais interrogou-se transponders passivos, obtendo-se ganhos de sensibilidade dos transponders maiores que 3 dB. Uma vez que a amplificação de sinais de elevado PAPR é uma operação crítica, propôs-se também novas arquiteturas eficientes de transmissão baseadas na combinação de sinais em espaço livre. Esta tese aborda também outros aspetos não menos importantes, como o self-jamming em leitores RFID passivos, tido como o segundo fator limitativo neste tipo de sistemas. Estudou-se técnicas de cancelamento de self-jamming CW e estendeu-se o conceito a sinais MS, tendo-se obtido isolamentos entre o transmissor e o recetor de até 50 dB no primeiro caso e de até 60 dB no segundo. Finalmente, com o objetivo de demonstrar uma aplicação prática dos conceitos de transmissão de energia sem fios e comunicação backscatter, desenvolveu-se um sistema de controlo remoto sem pilhas, cujo protótipo foi integrado num televisor comercial a fim de controlar quatro funcionalidades básicas (CH+,CH-,VOL+,VOL-)

A self-powered single-chip wireless sensor platform

Internet of things” require a large array of low-cost sensor nodes, wireless connectivity, low power operation and system intelligence. On the other hand, wireless biomedical implants demand additional specifications including small form factor, a choice of wireless operating frequencies within the window for minimum tissue loss and bio-compatibility This thesis describes a low power and low-cost internet of things system suitable for implant applications that is implemented in its entirety on a single standard CMOS chip with an area smaller than 0.5 mm2. The chip includes integrated sensors, ultra-low-power transceivers, and additional interface and digital control electronics while it does not require a battery or complex packaging schemes. It is powered through electromagnetic (EM) radiation using its on-chip miniature antenna that also assists with transmit and receive functions. The chip can operate at a short distance (a few centimeters) from an EM source that also serves as its wireless link. Design methodology, system simulation and optimization and early measurement results are presented

Chipless RFID sensor tag system with microstrip transmissionline based ID generation schemes

This dissertation presents a chipless radio frequency identification (RFID) sensor tag system consisting of passive chipless RFID sensor tags and specialized reader. The chipless sensor tags are fabricated on a flexible substrate and contain an ID generation circuit, a sensor, and a microstrip antenna. The ID generation circuit consists of meandered microstrip transmission lines and uses a novel reflection and delay based ID generation scheme. The scheme, using an input RF pulse, constructs an on-off keying (OOK) or pulse position modulated (PPM) signal pattern representing a unique ID code. Two transmission lines and OOK representation are used and the generation of ten different ID codes are demonstrated. The integrated ID generation circuit, sensor, and antenna use a single transmission line and PPM representation, and demonstrate the generation of eight different ID codes. However, the presented schemes allow the generation of higher combinations of bits. A practical method to measure radar cross section (RCS) parameters of antennas that provides complete and more accurate information on scattering properties of antennas, essential for chipless sensor tag design, is presented. The new method uses minimum mean square error estimation solution of a derived received backscattered signal power equation and provides load independent structural-mode RCS, antenna-mode RCS, and relative phase factor of the measured antenna. Two configurations of the chipless sensor tags configuration-I (conf-I) and configuration-II (conf-II) are presented. In conf-I tags, sensors are connected as a load to the antenna and the sensor information is amplitude modulated in the backscattered signal. The testing with conf-I temperature sensor tag resulted in a 28% amplitude change when the temperature at the tag changes from 27°C to 140°C. In conf-II tags, sensors are connected as load to the ID generation circuit and the sensor information is phase modulated in the antenna-mode scattered signal. With the conf-II ethylene sensor tag, a phase change of 33° is observed when the ethylene concentration at the tag changes from 0 to 100 ppm. The specialized reader system is comprised of an analog reader that wirelessly communicates with the sensor tags and a single board computer that computes the sensor information from the received signal. The reader system constructs a 96 bit serialized global trade item number (SGTIN-96) electronic product code (EPC) format unique RFID tag data frame, including 16 bit sensor information, and makes the information available on a secure web interface accessible from cyberspace. The presented sensor tag system has the advantages of passive and chipless sensor tag operation, while offering a wide range of sensors types for integration. Moreover, it offers a viable alternative solution to existing active as well as passive RFID sensor tag systems (eg. SAW based RFID sensor tag systems)

A Miniaturized Low Power Millimeter Wave RFID tag for Spatial Localization and Detection

The work outlined in this thesis investigates the applicability of millimeter wave semi-passive backscatter nodes for use in the spatial localization and tracking of objects at short distances. A miniaturized semi-passive ultra-low power energy autonomous RFID tag operating in the 24 GHz ISM frequency band is developed. The spatial localization of the RFID tags is enabled by the use of a Frequency Modulated Continuous Wave (FMCW) Radar as the reader. The radar is used to resolve the modulated backscatter returned by the RFID tags when interrogated by a Continuous Wave from the reader.M.S

Non-linear shunt regulator based on a PWM RF power detector for RFID applications

Radio Frequency Identification (RFID) is utilized in a variety of applications, includ ing tagging animals and objects to make their identification (ID) easier to read and man age, similar to a bar code or QR code. In this regard, the goal of this research is to improve RFID transponder power regulation in order to increase reader distance. This thesis de scribes a non-linear shunt regulator that employs a Radio Frequency (RF) power detector based on the Pulse Width Modulation (PWM) technique to aim magnetically coupled RFID transponders. A quick voltage-clamp loop and a slow-accurate power detector loop are used in the proposed regulator architecture. The first loop ensures over-voltage pro tection, while the second loop gradually corrects the first loop’s imprecision based on the measured input power. To contextualize the issues and improvements of the new design, the state-of-the-art in RFID power management and RF power detector are covered first. The new architecture is specified after theoretical development, electrical simulations, and the design of the new architecture is implemented. The entire regulator design was prototyped as part of a commercial low-frequency (134 kHz) RFID transponder in a 180 nm CMOS process. The regulator deal with a sinusoidal voltage at its input generated by the LC tank that extracts energy from the reader to supply its circuitry. The use of a 3.3V standard process for the analog circuitry in order to decrease the fabrication cost by not using the high voltage module (5 V for example) complicates the system design. Even though the proposed solution aims to regulate the input voltage precisely at 3.6 V maximum, the maximum voltage supported by 3.3 V standard module using two feedback is achieved. The total RFID transponder area of 870x870 µm² was obtained, with 130x230 µm² related to the regulator circuit area only. Both resonant and supply capacitors are imple mented on the chip. The complete system consumes a maximum current of 4.5 µA, over a wide RF input power range that is modulated by the distance between the reader and the transponder. As the power detector corrects the imprecision of the shunt regulator com posed by simple diodes due to its process, voltage and temperature (PVT), the transponder performance was measured with and without the shunt regulator enabled. Results show an improvement of 16.7 % in the communication distance between the transponder and the reader.Identificação por Rádio Frequência (RFID) é usada em muitas aplicações, colocando etiquetas eletrônicas em animais e objetos para facilitar a leitura a fim de melhorar o gerenciamento destes. Nesse contexto, essa dissertação tem como objetivo melhorar a regulação de potência em chips de RFID a fim de aumentar a distância de leitura. Essa dissertação apresenta um nova arquitetura de regulador paralelo, não linear, que usa um detector de potência de Rádio Frequência (RF) baseado em uma técnica de modulação de pulso (PWM) para aplicação de RFID que usam o princípio de comunicação por acopla mento magnético. A arquitetura de regulador proposto é composta de duas realimen tações: uma realimentação usa um limitador de tensão rápido e a outra usa um detector de potência lento porém preciso. O primeiro garante a proteção contra sobre tensão e o segundo corrige a imprecisão do primeiro de acordo com a potência do sinal de entrada. Primeiramente, o estado da arte em regulação de sitemas de RFID bem como em detectores de potência RF são feitos para contextualizar os problemas e melhorias da nova arquitetura. Um desenvolvimento teórico seguido por simulações elétricas e o projeto do circuito da nova arquitetura de regulador paralelo são abordadas em detalhes. A circuito foi implementado em um processo CMOS de 180 nm como parte de um Chip de RFID de baixa frequência (134 kHz). O regulador lida com uma tensão senoidal (134 kHz) na sua entrada, gerada por um tanque LC que extrai energia provinda do leitor e que é usada alimentar todo o chip. Devido ao uso de um processo padrão 3.3 V CMOS para implementação do circuitos analógicos a fim de diminuir o custo de fabricação com o não uso do modulo de alta tensão (Ex. 5 V), impondo dificuldades no projeto do sistema, mesmo assim a solução proposta regula a tensão de entrada do chip em 3.6 V, máxima suportada pela tecnologia, com o uso das duas malhas de realimentação. A área total do Chip de RFID é de 870x870 µm², com 130x230 µm² para apenas o circuito de regulação. Os capacitores de ressonância e de alimentação foram integrados no Chip. O sistema completo consome 4.5 µA, sobre uma ampla gama de potência de entrada que é modulada pela distância entre o leitor e a tag. Como o detector de potência corrige a imprecisão do limitador de tensão composto de diodos devido a variação em processo, tensão e temperatura (PVT), a distância de leitura foi medida com e sem o detector de potência habilitado. Os resultados mostraram uma melhoria de 16.7 % na distância de comunicação