Surface Acoustic Wave Radio Frequency Identification Research Articles

SAW RFID Tag Spatial Division Multiple Access Based on 3D Reflector Response Localization Using a Wideband Holographic Approach

Surface acoustic wave (SAW) radio-frequency identification (RFID) has high potential for industrial applications, where automated identification and localization of assets represent the backbone of process controlling and logistics. However, in situations where multiple tags are simultaneously interrogated, the response patterns corresponding to the hard-coded reflectors are prone to overlap, preventing their association with the corresponding tags and, hence, the correct tag decoding. Identification and localization of multiple SAW RFID tags are addressed in this work under this challenging effect, known as collision, with a multi-antenna mobile robot-based synthetic aperture approach. Using the estimation of the spatial probability density functions of the SAW tag reflectors over a given interrogation aperture, the received impulse responses can be resolved in three dimensions and clustered with respect to their estimated locations. The performance of the proposed approach to associate and localize the signals from multiple tags was evaluated theoretically and experimentally.

SAW Tags With Enhanced Penetration Depth for Buried Assets Identification (Aug. 2020)

To identify buried assets, this article presents a novel design of surface acoustic wave (SAW) tag to enhance its underground penetration capacity. A penetration depth model for a SAW tag buried in materials is established to investigate the depth of detection and guide the design of the SAW tag. Multipulse position with all reflectors in two groups (MPP-ART) coding scheme is proposed to reduce the insertion loss of the SAW chip. A novel embedded monopole microstrip tag antenna is investigated with a stable frequency performance when embedded in diverse types of materials. Furthermore, a linear frequency modulation pulse compression transceiver based on software defined radio is implemented to enhance the penetration depth. The insertion loss of the SAW chip at 920 MHz with the MPP-ART coding scheme, is reduced to 26.58 dB. Through experiments, the penetration depth of the SAW radio frequency identification prototype has reached 0.75 m in river water, 0.8 m in tap water, 1.5 m in wet sand, and 3 m in dry sand, respectively. The experimental results demonstrate that the SAW tag can work in various materials with good penetration depth, relatively immune to electromagnetic interference with adjacent metallic objects, making it suitable for the identification of buried assets for industrial applications.

Multi-Channel Real-Time Condition Monitoring System Based on Wideband Vibration Analysis of Motor Shafts Using SAW RFID Tags Coupled with Sensors.

While there is a wide range of approaches to monitor industrial machinery through their static components, rotating components are usually harder to monitor, since sensors are difficult to be mounted on them and continuously read during operation. However, the characteristics of rotating components may provide useful information about the machine condition to be included in monitoring algorithms, specially for long-term data analysis. In this work, wireless vibration monitoring of rotating machine parts is investigated using surface acoustic wave (SAW) radio frequency identification (RFID) tags coupled with sensors. The proposed augmented transponder solution, combined with low-latency interrogation and signal processing, enables real-time identification and wideband vibration sensing. On top of that, a multi-channel interrogation approach is used to compensate motion effects. This approach enhances the signal-to-noise ratio of low-power high-frequency components present on the vibration signatures and enables discriminant information extraction from rotating machine parts. Final feasibility is evaluated with induction motors and vibration measurements on rotating shafts are verified. In addition, a condition classification algorithm is implemented in an experimental setup based on different motor states. The results of this work open the possibility to feed predictive maintenance algorithms using new features extracted in real-time from wideband vibration measurements on rotating components.

Custom PXIe-567X-Based SAW RFID Interrogation Signal Generator

This paper presents a fully reconfigurable and reliable PXIe-567X software-defined interrogation signal generator for surface acoustic wave (SAW)-based passive radio frequency identification (RFID). Contrary to most commercial SAW RFID readers that operate only at a unique predefined frequency, the proposed vector signal generator is aimed to operate at any frequency defined by the user, from 85 MHz to 6.6 GHz, including the 902–928 MHz and 2.45-GHz industrial scientific and medical bands. The PXIe-567X-based signal generator can accurately generate not only conventional ON–OFF keying (OOK)-modulated or pulsed binary phase shift keying (BPSK)-modulated SAW RFID interrogation signals, but also completely user-defined interrogation signals. A custom LabVIEW user interface that allows to control the carrier frequency, the power, and the waveform of the interrogation signal has been designed. The operator can switch between custom waveforms without resetting and reprogramming the whole system. The proposed RFID request signal generator has been validated using a complete measurement setup. Time-domain and frequency-domain validation tests of OOK modulated and wideband pulsed BPSK-modulated signal generation have been conducted at 170, 340, 915 MHz and 2.45 GHz. Very accurate results have been obtained. The PXIe-567X-based RFID interrogator has been tested with a fabricated 3-b SAW RFID tag. The operability of the entire SAW RFID system has been demonstrated.

SAW-RFID enabled temperature sensor

Wireless sensors based on surface acoustic wave (SAW) technology has its own advantages over its counterparts. In this paper, a novel SAW radio frequency identification (RFID) enabled temperature sensor is proposed for industrial applications, in which short measurement range but high accuracy is usually required. The encoding scheme for the sensor using pulse positions combined with phase information is adopted, and then the relationship between the length of a time slot and the decoding errors is deduced to ensure the sensor can be accurately identified, even though ambient temperature fluctuates. In order to solve the phase ambiguity problem involved in temperature measurements more efficiently and reduce the cost of obtaining the unwrapping temperature characteristic curves in the calibration process, an analytical procedure for calculating the variation of phase delay differences with respect to temperature has been proposed. A self-developed burst transceiver supporting online data analysis is also presented. The experimental results demonstrate the effectiveness and practicality of the proposed SAW-RFID enabled temperature sensing scheme, and the prototype sensor within a temperature-controlled oven 2m away from the center of the transceiver antenna in a horizontal orientation achieves an accuracy of ±0.3°C in the temperature range 0–40°C.

Design and implementation of high data capacity RFID tag using eight-phase encoding

Enhancing the data capacity of surface acoustic wave (SAW) radio frequency identification (RFID) tags using the combination of time position and phase encoding with fewer number of reflectors is investigated in this work. Simulation and fabrication of SAW RFID tags are performed using COMSOL Multiphysics and standard photolithography process. Lithium Tantalite (LiTaO3) is used as a substrate and Aluminium metal electrodes are used to realise the interdigital transducer (IDT) electrodes. The data capacity enhancement is tested using a SAW RFID tag consisting of a single-phase unidirectional transducer (SPUDT) transducer and four code reflectors. By designing the width of SPUDT electrodes and floating electrodes and proper positioning of reflectors, eight phases (i.e. 0°, −45°, −90°, −135°, −180°, −225°, −270° and −315°) are detected which correspond to 3 bits of data per reflector. These eight phases would result to have one more data bit per reflector. Therefore, eight phase states along with four time positions lead to 32 different states (i.e. 5 bits of data per reflector). To facilitate the realisation of our idea, the fabrication process has been performed at 250 MHz; however, it can easily be implemented at higher frequencies (i.e. GHz range).

An SNR improvement of passive SAW tags with 5-bit Barker code sequence

Passive surface acoustic wave (SAW) tags require a large signal-to-noise ratio (SNR) in order to increase the interrogation range. For the purpose of achieving high SNR for radio frequency identification (RFID) communication systems, Barker codes, a binary phase shift keying (BPSK) modulation technique, have been adopted in this study. Passive SAW RFID tags were designed with 5-bit Barker code sequences to generate BPSK modulated signals. Through the SNR analysis, the improvements in SNR were about 11 dB using Barker codes along with a correlator, which can be further improved by optimisation in the correlator.

Temperature Measurements on Hot Spots of Power Substations Utilizing Surface Acoustic Wave Sensors

In several applications in the field of metrology, the direct connection of the sensor element with the respective signal-processing unit of the measurement system is not trivial. It can be mentioned, as an example, the measurement of hot points in electric power substations because of the high electrical potential. To solve that problem, two alternatives were studied, one using active surface acoustic wave (SAW) sensors and other using passive SAW tags. For the passive sensor, a SAW radio-frequency identification (RFID) temperature detector was used. That technology is widely applied for typical transport identification (grain transportation, road traffic control), but its application in the field of metrology is innovative. The variation in temperature makes an alteration in the characteristics of the piezoelectric material of the SAW matrix, changing mostly the resonance frequency. Using SAW–RFID, the problem of measuring temperature basically is directed to the identification of the frequency of resonance of the SAW. The use of active SAW sensors has been demonstrated to be much more satisfactory for the solution of such a problem because of the limitation in the range of the passive sensors.

Inline SAW RFID tag using time position and phase encoding

Surface acoustic wave (SAW) radio-frequency identification (RFID) tags are encoded according to partial reflections of an interrogation signal by short metal reflectors. The standard encryption method involves time position encoding that uses time delays of response signals. However, the data capacity of a SAW RFID tag can be significantly enhanced by extracting additional phase information from the tag responses. In this work, we have designed, using FEM-BEM simulations, and fabricated, on 128 degrees -LiNbO3, inline 2.44-GHz SAW RFID tag samples that combine time position and phase encoding. Each reflective echo has 4 possible time positions and a phase of 0 degrees , -90 degrees , -180 degrees , or -270 degrees. This corresponds to 16 different states, i.e., 4 bits of data, per code reflector. In addition to the enhanced data capacity, our samples also exhibit a low loss level of -38 dB for code reflections.

Z-path SAW RFID tag

Surface acoustic wave (SAW) radio-frequency identification (RFID) tags are soon expected to be produced in very high volumes. The size and cost of a SAW RFID tag will be key parameters for many applications. Therefore, it is of primary importance to reduce the chip size. In this work, we describe the design principles of a 2.4-GHz SAW RFID tag that is significantly smaller than earlier reported tags. We also present simulated and experimental results. The coded signal should arrive at the reader with a certain delay (typically about 1 micros), i.e., after the reception of environmental echoes. If the tag uses a bidirectional interdigital transducer (IDT), space for the initial delay is needed on both sides of the IDT. In this work, we replace the bidirectional IDT by a unidirectional one. This halves the space required by the initial delay because all the code reflectors must now be placed on the same side of the IDT. We reduce tag size even further by using a Z-path geometry in which the same space in x-direction is used for both the initial delay and the code reflectors. Chip length is thus determined only by the space required by the code reflectors.

2D localisation using SAW-based RFID systems: a single antenna approach

This paper presents a novel Real-Time Localisation System (RTLS) based upon 2.45 GHz Surface Acoustic Wave (SAW) Radio Frequency Identification (RFID) systems. The system utilises a novel localisation method that combines the angular rotation of the RFID reader's antenna system with the inherent Time-of-Flight (TOF) distance measurement capabilities of the SAW RFID system. The system design rests upon the sound physical fundamentals of electromagnetic radiation and SAW operation. The system was implemented and empirically evaluated. It was determined to provide accurate 2-Dimensional (2D) location of the SAW tag that is within 3.17 cm of the actual location for a reader to tag range of up to 10 m.