Backscatter Modulation Research Articles

Wireless passive photo detector for insect tracking

This letter presents a passive wireless photo detector for precise localization of insects in biological studies. The detector is based on a photo diode matched to an antenna, and it produces modulated backscattering of microwaves when illuminated with amplitude modulated light. The radar cross section of the detector is derived and the concept is experimentally verified at 1.5 GHz. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:2312–2315, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25427

Analysis and design of power efficient semi-passive RFID tag

The analysis and design of a semi-passive radio frequency identification (RFID) tag is presented. By studying the power transmission link of the backscatter RFID system and exploiting a power conversion efficiency model for a multi-stage AC–DC charge pump, the calculation method for semi-passive tag's read range is proposed. According to different read range limitation factors, an intuitive way to define the specifications of tag's power budget and backscatter modulation index is given. A test chip is implemented in SMIC 0.18 μm standard CMOS technology under the guidance of theoretical analysis. The main building blocks are the threshold compensated charge pump and low power wake-up circuit using the power triggering wake-up mode. The proposed semi-passive tag is fully compatible to EPC C1G2 standard. It has a compact chip size of 0.54 mm2, and is adaptable to batteries with a 1.2 to 2.4 V output voltage.

UWB ranging in passive UHF RFID: proof of concept

A proof of concept for ultra-wideband (UWB)-based ranging in passive UHF RF identification (RFID) is presented. The proposed method uses the tag's backscatter modulation and thus does not require processing of the UWB signal by the tag. It is evaluated using measurements in an indoor environment similar to a warehouse portal in terms of channel impulse responses. The ranging accuracy is comparable to classical UWB ranging and thus inherently robust to multipath propagation.

Self-aligning wireless link using modulated backscatter

A self-tracking (aligning) radio communications system based on the principle of modulated backscatter detection is presented here. Using amplitude-modulated backscatter from a co-operating target, a modified IQ demodulation scheme is used to reproduce automatically and in real time both the received and conjugate of the received phase of an incoming signal. The phase conjugated demodulated IF signal can have incoming backscattered data removed and new data are inserted before being up-converted using IQ single side-band generation so that retro-directive re-transmission can be made to occur. In the absence of the backscattered modulation signal, no phase conjugation and hence no retro-directed re-transmission can occur. The system reported is therefore inherently self-authenticating a facility not readily available from previously reported retro-directive self-tracking systems.

Reflection/transmission tuner analysis and applications

The authors present analysis and applications of a versatile coupled-line-based impedance tuner suitable for use in reflection or transmission mode. The impedance tuner can be used to implement complex backscatter modulation schemes for RFID applications while simultaneously tuning the tag antenna in the presence of external loading. A high isolation band-tunable quasi-circulator is developed, which employs the impedance tuner to provide mismatch and leakage cancellation. The quasi-circulator features a peak isolation of over 60 and 30 dB isolation bandwidth of over 5%. The isolation can be tuned across a bandwidth of over 40%.

A Fully Integrated 900-MHz Passive RFID Transponder Front End With Novel Zero-Threshold RF–DC Rectifier

This paper presents a fully integrated CMOS analog front end for a passive 900-MHz radio-frequency identification (RFID) transponder. The power supply in this front end is generated from the received RF electromagnetic energy by using an RF-dc voltage rectifier. In order to improve the compatibility with standard CMOS technology, Schottky diodes in conventional RF-dc rectifiers are replaced by diode-connected MOS transistors with zero threshold. Meanwhile, theoretical analyses for the proposed rectifier are provided and verified by both simulation and measurement results. The design considerations of the pulsewidth-modulation (PWM) demodulator and the backscatter modulator in the front end are also discussed for low-power applications. The proposed front end is implemented in a 0.35-mum 2P4M CMOS technology. The whole chip occupies a die area of 490 times 780 mum2 and consumes only 2.1 muW in reading mode under a self-generated 1.5-V supply voltage. The measurement results show that the proposed rectifier can properly operate with a -14.7-dBm input RF power at a power conversion efficiency of 13.0%. In the proposed RFID applications, this sensitivity corresponds to 10.88-m communication distance at 4-W equivalent isotropically radiated power from a reader base station.

UHF 대역 장거리용 RFID 태그에 관한 연구

RFID 기술은 각 사물에 전자 태그를 부착하고, 사물의 고유 ID를 무선으로 인식하여, 해당 정보를 수집, 저장, 가공, 추적하는 기술로 다양한 분야에 적용되고 있다. 이러한 RFID 시스템을 설계하는데 있어 리더가 태그 정보를 인지할 수 있는 인식 거리는 중요한 파라미터 중 하나이다. 본 논문에서는 UHF 대역 RFID 시스템의 장거리 인식 거리에 요구되는 태그를 설계하는 새로운 방법을 제안하였다. 제안한 방법에 따른 태그는 순방향 인식 거리를 확장하기 위해 전지 지원형 형태로 설계되었으며, 역방향 인식 거리를 확장하기 위해 역산란 변조 신호를 증폭하였다. 제작된 태그의 최소 문턱 전력은 -23 dBm, 역산란 증폭 이득은 28 dB임을 측정 결과를 통해 확인하였으며, 이는 시뮬레이션 결과와 일치한다. 본 논문에서 제안한 태그의 인식 거리는 상용 태그와 비교하여 2배 이상 향상되었다. RFID technologies, which allow collecting, storing, processing, and tracking information by wirelessly recognizing the inherent ID of object through an attached electronic tag, have a variety of application areas. One of the important parameters in designing such RFID systems is the read range within which the system recognizes the electronic tag. We present a novel method of designing an RFID tag required for long read range of RFID systems. The tag designed by the proposed method is battery-assisted to increase its forward-link read range and simultaneously, has backscattering modulation amplified to increase its reverse-link read range. We experimentally confirm that the minimum threshold power of the tag is - 23 dBm and the backscattering modulation gain is 28 dB, which is consistent with our simulation results. We also verify that the tag in this paper improves more than 2 times in terms of the read range compared to the existing commercial tags.

Design and Implementation of a Long-Range RFID Reader for Passive Transponders

This paper presents a long-range RF identification (RFID) reader that has proven to work at up to 5 m with 2-W effective radiated power transmit power at 868 MHz. For the validation, a phase-shift keying backscatter modulator has been implemented, thus complementing the reader to form a complete passive RFID system focused on backscattering communication. The system has been first analyzed by means of a simulation tool, and as a result, reader design considerations are derived. Guidelines for the design of the backscatter modulator are also put forward. The reader and modulator have been fabricated and two measurement setups have been built to validate the reader performance. First, the system has been tested without antennas; -61.6-dBm reader sensitivity with only 11 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">deg</sup> phase difference has been measured. Finally, both the reader and modulator have been complemented with their respective antennas and the system has been evaluated in a real scenario. Reflections and interferences are demonstrated to degrade reader performance; nevertheless read ranges up to 8.1 m have been measured.

Communication coverage in wireless passive sensor networks

System lifetime of wireless sensor networks (WSN) is inversely proportional to the energy consumed by critically energy-constrained sensor nodes during RF transmission. In that regard, modulated backscattering (MB) is a promising design choice, in which sensor nodes send their data just by switching their antenna impedance and reflecting the incident signal coming from an RF source. Hence, wireless passive sensor networks (WPSN) designed to operate using MB do not have the lifetime constraints of conventional WSN. However, the communication performance of WPSN is directly related to the RF coverage provided over the field the passive sensor nodes are deployed. In this letter, RF communication coverage in WPSN is analytically investigated. The required number of RF sources to obtain interference-free communication connectivity with the WPSN nodes is determined and analyzed in terms of output power and the transmission frequency of RF sources, network size, RF source and WPSN node characteristics.

Antenna Effective Aperture Measurement With Backscattering Modulation

A scattering measurement method for antenna characterization is described. The antenna backscattering is modulated by an oscillator circuit. The modulation begins, when a known RF power is transferred to the oscillator circuit from the antenna. This enables the measurement of the effective aperture of the antenna, from which the antenna bandwidth and radiation pattern are obtained. A theory for antenna aperture measurement is developed using a simple circuit model for the antenna-oscillator system. A dipole and a PIFA with a reactive input impedance at the application frequency were measured. The antenna aperture was measured to an accuracy of 9%, and the measurements complied with simulated and measured references. The method provides simple and accurate bandwidth and radiation pattern measurements with the reactive load the antenna is designed to work with.

EPCglobal Gen-2 RFID 시스템 태그와 리더간의 무선 전송 방식 성능 분석

In this paper, we analyze the performance of the encoding and the modulation processes in the downlink and uplink of the EPCglobal Gen-2 system through the analysis and simulation. Furthermore, the synchronization issues on time and frequency domain and the preamble architecture are evaluated. By incorporating the encoding and the modulation technigue in the downlink and uplink, we assess the performance of the EPCglobal Gen-2 system. We also introduce the encoding and backscatter modulation process as well as the BER performance of FM0 code. In addition, the importance and the role of the frequency and time synchronization, such as the preamble and frame synchronization are explained. Through the simulation in the uplink on the detection probability through preamble, we find that the detection probability approaches 1 for 13 dB .

A Frequency Diverse Gen2 RFID System with Isolated Continuous Wave Emitters

The “Gen2” specification for UHF passive RFID systems released by EPCglobal has become an intense research interest. A Gen2 tag derives its power from the RF wave emitted by a Gen2 RFID reader and responds its modulated backscatter signals to the reader. Due to the large propagation loss, the accessible range of a Gen2 tag is hence limited. Moreover, the readability of a Gen2 tag is often influenced by the multipath fading problem. In order to mitigate the problems, a multi-carrier UHF passive RFID system utilizing the frequency diverse backscatter ability of a Gen2 tag is proposed in a prior work. In this work, a thorough analysis of the system is given. Especially, the appropriate powers of the transceiver and CWEs are derived to make the system more feasible in practical applications.

Radar Cross-Section Analysis of Backscattering RFID Tags

In this letter, we present a graphical method based on Green's analysis of scattering antennas to optimize the load impedances for achieving maximum modulated radar cross-section (RCS) of backscattering radio-frequency identification (RFID) tags. A planar tag antenna specifically designed for working in the ultra-high-frequency band is used to experimentally validate the method. The measured RCS of the loaded tag antenna shows acceptable agreement with the theory and simulated results. This method is especially valuable to the design of semipassive RFID tags when the communication range is solely determined by the backscattering modulation efficiency of tags.

A System Desgin for the Reader of Microwave Radio Frequecy Identification

RFID (Radio Frequency Identiflcation) is now attracting many interests for its bright future in commercial and daily use. For the low-frequency (LF, typically 125KHz) and the high-frequency (HF, typically 13.6MHz) RFIDs, the Readers have already come into our daily life out of their matured technologies, while the ultra-high frequency (UHF) RFID Readers are still in the process for the reliability and functionality. This paper represents a systematic design of a UHF RFID reader. Received backscatter modulation waves (carrier wave frequency 915MHz) are directly demodulated to baseband signals using the Zero IF technology. The reader is designed as a quadrature (I/Q) one, which can avoid null points of the received signals (4) and enhance the demodulation sensitivity. DOI: 10.2529/PIERS061129101136

Detection sensitivity of self-pulsed self-oscillating millimetre-wave sensor

A self-pulsed, self-oscillating detector sensor based on a gallium arsenide reflection amplifier monolithic microwave integrated circuit and microstrip patch antenna is presented. The sensor, which can detect signals as low as −120 dBm in a 30 Hz bandwidth at modulated backscatter frequencies above 20 kHz, operates at 19.8 GHz and requires a single 3.7 V DC bias supply.

Cross‐slot coupled elliptical patch antenna circularly polarized for localization

AbstractThis paper reports a circularly polarized cross‐slot coupled elliptical patch antenna for implementation in a new radio‐frequency identification and localization system currently under development. The radio‐frequency localization system in this work is composed of a reader and a semiactive tag (a battery feeds the tag to increase its reading range but the backscattering modulation principle is used to decrease its power consumption). The overall system is designed in the ISM frequency band of 5.8 GHz. This frequency band is a good compromise that permits a large bandwidth and a good range for use in a local positioning system (∼10 m). This antenna is to be used by the reader as its radiation pattern is semispherical. It provides the circular polarization required by the targeted application to allow the tag identification within any physical position. The antenna bandwidth and axial ratio were enhanced using a proper design and a cross‐slot feeding of the patch. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 336–339, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22136

The effect of wave breaking on surface wave imaging by Synthetic Aperture Radar

The effect of ocean wave breaking as a non-Bragg mechanism on backscattering cross-section and modulation transfer functions (MTF) of radar was investigated based on Bragg resonance theory and parametric method. The result showed that the additional effect of wave breaking on backscattering cross-section is not more than 20% except for the small incident angle of VV polarized electromagnetic (e.m.) wave but is significant for HH polarized e.m. wave. Breaking waves lead to increase in the modulus of tilt modulation MTF and the larger the wind speed, the faster the increase. For large incident angle, the modulus of tilt modulation MTF with wave breaking decreases quickly with incident angle of HH polarization and approach to that without wave breaking for VV polarization. The hydrodynamic MTF increases 30%–60% when considering wave breaking and the increase is larger for HH polarization than for VV polarization.

Ultra-low power PSK backscatter modulator for UHF and microwave RFID transponders

An integrated circuit implementation of a PSK backscatter modulator for passive radio frequency identification (RFID) transponders is proposed. Such modulator offers a significant reduction of the power consumption with respect to other schemes already presented in the literature. Furthermore, the topology of the proposed modulator allows us to control its output resistance so that only a negligible fraction of the active power at the antenna goes to the modulator.

Remotely powered addressable UHF RFID integrated system

This paper presents a fully integrated remotely powered and addressable radio frequency identification (RFID) transponder working at 2.45 GHz. The achieved operating range at 4 W effective isotropically radiated power (EIRP) base-station transmit power is 12 m. The integrated circuit (IC) is implemented in a 0.5 /spl mu/m silicon-on-sapphire technology. A state-of-the-art rectifier design achieving 37% of global efficiency is embedded to supply energy to the transponder. The necessary input power to operate the transponder is about 2.7 /spl mu/W. Reader to transponder communication is obtained using on-off keying (OOK) modulation while transponder to reader communication is ensured using the amplitude shift keying (ASK) backscattering modulation technique. Inductive matching between the antenna and the transponder IC is used to further optimize the operating range.

The history of RFID

Radio frequency identification (RFID) is an integral part of our life, which increases productivity and convenience. It is the term coined for short-range radio technology used to communicate mainly digital information between a stationary location and a movable object or between movable objects. This RFID system uses the principle of modulated backscatter where it can transfer the data from the tag to the reader. The tag generally reads its internal memory of stored data and changes the loading on the tag antenna in a coded manner corresponding to the stored data. RFID is a technology, which spans systems engineering, software development, encryption etc., and thus there are many engineers involved in the development and application of RFID and at present the shortage of technical and business people trained in RFID is hampering the growth of the industry.