Surface Acoustic Wave Transponder Research Articles

Development of chipless, wireless current sensor system based on giant magnetoimpedance magnetic sensor and surface acoustic wave transponder.

A chipless, wireless current sensor system was developed using a giant magnetoimpedance (GMI) magnetic sensor and one-port surface acoustic wave (SAW) reflective delay line for real-time power monitoring in a current-carrying conductor. The GMI sensor has a high-quality crystalline structure in each layer, which contributes to a high sensitivity and good linearity in a magnetic field of 3–16 Oe. A 400 MHz RF energy generated from the interdigital transducer (IDT)-type reflector on the one-port SAW delay line was used as an activation source for the GMI magnetic sensor. The one-port SAW delay line replaces the presently existing transceiver system, which is composed of thousands of transistors, thus enabling chipless and wireless operation. We confirmed a large variation in the amplitude of the SAW reflection peak with a change in the impedance of the GMI sensor caused by the current flow through the conductor. Good linearity and sensitivity of ~0.691 dB/A were observed for currents in the range 1–12 A. Coupling of Mode (COM) modeling and impedance matching analysis were also performed to predict the device performance in advance and these were compared with the experimental results.

Exploiting the combination of 3D polymer printing and inkjet Ag-nanoparticle printing for advanced packaging

A rapid advanced packaging concept, consisting of 3D photopolymer printing and Ag nanoparticle printing, was investigated for the construction of a simple radio frequency identification (RFID) package with integrated surface acoustic wave transponder (SAW). An acrylate-type SAW package housing was printed with a multi-jet 3D printer and the corresponding antenna for the wireless read-out was manufactured via inkjet printing of Ag nanoparticle ink. The corresponding Ag structure had a thickness of about 2μm with a sheet resistance of 250mΩsq−1 after the photonic sintering processing. The chip-on-board and flip-chip packaging concepts were pursued for connecting the antenna structure to the chip pads. The SAW package prototype in a flip-chip configuration showed a significant signal to noise ratio (SNR) of about 30dB via antenna-bridged radio frequency link at a moderate distance of 3cm.

High frequency passive micro-magnetic sensor based on surface acoustic wave transponder and giant magnetoimpedance sensitive element

This paper presents a high frequency micro-magnetic field sensor composed of a surface acoustic wave (SAW) transponder and a giant magnetoimpedance (GMI) sensitive element. The coupling-of-mode(COM) method is used to design and optimize the structure of the SAW transponder. An amorphous wire as the GMI element is used to conjunct with the SAW transponder. The experiment result shows the magnetic sensitivity of the sensor of 1.13dB/Oe changes when the magnetic sensitivity does not exceed 2.0Oe. For the two-dimension intensity measurement of the magnetic field, a two-dimension SAW-GMI sensor is developed and tested.

A study on the tire deformation sensor for intelligent tires

Tires are the most important components in driving safety. The necessity of the sensor mounted on the tire is gradually increasing. The purpose of this study is to design, fabricate, and install a deformation sensor inside the tire for getting the information from road. In order to achieve this, we focused on the design of a sensor structure and test of the sensor system with SAW (Surface Acoustic Wave) transponder mounted inside the tire. A deformation sensor has been proposed and analyzed for getting advanced structure. An analytic solution for a simple case has been obtained and compared with the results from computer simulation and then, a couple of improved models have been obtained from the analysis. With external loads in mind, the range of the pressure applied to the tire was between 0 and 58 psi (the normal pressure of tire = 30 psi). The system for a high rate signal telecommunication has been developed with the application for a wireless/batteryless deformation sensor. Finally, the fabricated sensor system has been installed in the tire of the real vehicle and tested for the feasibility to intelligent tires. This study concludes that the system is applicable after making minor improvements.

Optimization of Autonomous Magnetic Field Sensor Consisting of Giant Magnetoimpedance Sensor and Surface Acoustic Wave Transducer

This paper presents a novel autonomous thin film magnetic field sensor consisting of a tri-layer giant magnetoimpedance sensor and a surface acoustic wave transponder. Double and single electrode interdigital transducer (IDT) designs are employed and compared. The integrated sensor is fabricated using standard microfabrication technology. The results show the double electrode IDT has an advantage in terms of the sensitivity. In order to optimize the matching component, a simulation based on P-matrix is carried out. A maximum change of 2.4 dB of the reflection amplitude and a sensitivity of 0.34 dB/Oe are obtained experimentally.

Integration of thin film giant magnetoimpedance sensor and surface acoustic wave transponder

Passive and remote sensing technology has many potential applications in implantable devices, automation, or structural monitoring. In this paper, a tri-layer thin film giant magnetoimpedance (GMI) sensor with the maximum sensitivity of 16%/Oe and GMI ratio of 44% was combined with a two-port surface acoustic wave (SAW) transponder on a common substrate using standard microfabrication technology resulting in a fully integrated sensor for passive and remote operation. The implementation of the two devices has been optimized by on-chip matching circuits. The measurement results clearly show a magnetic field response at the input port of the SAW transponder that reflects the impedance change of the GMI sensor.

Development of a passive and remote magnetic microsensor with thin-film giant magnetoimpedance element and surface acoustic wave transponder

This paper presents the development of a wireless magnetic field sensor consisting of a three-layer thin-film giant magnetoimpedance sensor and a surface acoustic wave device on one substrate. The goal of this integration is a passive and remotely interrogated sensor that can be easily mass fabricated using standard microfabrication tools. The design parameters, fabrication process, and a model of the integrated sensor are presented together with experimental results of the sensor.

Theoretical Analysis of Wireless Passive Impedance-Loaded SAW Sensors

This paper concentrates on the theoretical analysis of wireless passive surface acoustic wave (SAW) impedance-loaded sensors. A general method is proposed for simulating the impedance-loaded SAW sensors. It is based on the combined finite-element method and boundary element method (FEM/BEM). A FEM is used to account for the mass loading effect of electrodes and a Green's function is used to model the piezoelectric substrate. Comparison between the simulations and measurements on SAW devices shows a good agreement. The calculated amplitude variation of the impulse response in time domain shows a resonant characteristic with the change of the loaded impedance. It is found that the return loss reaches the maximum value when the resonant frequency of the loaded circuits matches the center frequency of the short-circuited SAW transponder. This phenomenon is successfully explained by using the proposed model. Some high-performance sensors with greater amplitude modulation and larger sensitive range could be designed using this method.

A radioisotope-powered surface acoustic wave transponder

We demonstrate a 63Ni radioisotope-powered pulse transponder that has a SAW (surface acoustic wave) device as the frequency transmission frequency selector. Because the frequency is determined by a SAW device, narrowband detection with an identical SAW device enables the possibility for a long-distance RF-link. The SAW transponders can be buried deep into structural constructs such as steel and concrete, where changing batteries or harvesting vibration or EM energy is not a reliable option. RF-released power to radioisotope- released power amplification is 108, even when regulatory safe amounts of 63Ni are used. Here we have achieved an 800 µW pulse (315 MHz, 10 µs pause) across a 50 Ω load every 3 min, using a 1.5 milli-Ci 63Ni source.

Wireless measurement of temperature using surface acoustic waves sensors

Surface acoustic wave (SAW) devices can be used as wireless sensor elements, called SAW transponders, for measuring physical quantities such as temperature that do not need any power supply and may be accessed wirelessly. A complete wireless sensor system consists of one or more such SAW transponders and a local radar transceiver. The SAW transponder receives an RF burst in the VHF/UHF band transmitted by the radar transceiver. The reader unit performs a radar measurement of the impulse response of the SAW transponder via a high-frequency electromagnetic radio link. A temperature variation changes the SAW velocity and thereby the response pattern of the SAW device. By analyzing the time delay between backscattered pulses with different time delays we get a rough estimation of the temperature of the SAW transponder. By using this information the ambiguity of +/-2pi in the phase differences between the pulses can be eliminated, which provides an overall and unambiguous temperature resolution of +/-0.2 degrees C.

SAW-based radio sensor systems

Surface acoustic wave (SAW) devices can be used as identification and sensor elements (SAW transponders) for mea- suring physical quantities such as temperature, pressure, torque, acceleration, humidity, etc., that do not need any power supply and may be accessed wirelessly. The complete wireless sensor system consists of such a SAW transponder and a local radar transceiver. An RF burst transmitted by the radar transceiver is received by the antenna of the SAW transponder. The passive transponder responds with an RF signal—like a radar echo—which can be received by the front-end of the local transceiver. Amplitude, frequency, phase and time of arrival of this RF response signal carry information about the SAW reflection and propagation mechanisms which in many cases can be directly attributed to the sensor effect for a certain measurand. Usually no intersymbol interference (ISI) due to environmental echoes occur, due to the high delay time of the SAW transponder in the order of some s. The present work reviews the operating principles of such sensor systems and their state-of-the-art performance by way of some examples which include the wireless measurement of temperature, pressure, torque, acceleration, tire-road friction, magnetic field, and water content of soil. Index Terms—Acceleration, local radar transceiver, magnetic field, passive SAW transponder for sensing, pressure, temper- ature, tire-road friction, torque, water content of soil, wireless measurement.

Passive wirelessly requestable sensors for magnetic field measurements

A direction-sensitive micro-magnetic field sensor is developed using the giant magneto-impedance (GMI) effect in a 30-μm diameter amorphous FeCoSiBNd wire. Consisting of a micro-sized zero-magnetostrictive amorphous wire of about 70-μm length, the GMI sensor was connected to a self-oscillating Colpitts oscillator circuit by laser welding. It shows a high sensitivity with a resolution of 100 nT for DC fields, quick response, and a high temperature stability. Reproducible measurements of a surface-flux distribution of mechanically 100 μm structured magnetic bar codes were carried out. Surface Acoustic Wave (SAW) devices are shown as passive, radio-requestable sensor devices. A new type employs the electrical load of the SAW device by the impedance of conventional sensors. In order to develop a wirelessly interrogable magnetic field sensor, the combination of the GMI sensors and SAW transponders is discussed and the results are shown.

Wirelessly interrogable magnetic field sensor utilizing giant magneto-impedance effect and surface acoustic wave devices

A micro-magnetic field sensor is developed using the giant magneto-impedance (GMI) effect in a 30 /spl mu/m diameter amorphous FeCoSiBNd wire of zero magnetostriction. Surface Acoustic Wave (SAW) devices are described as passive, radio requestable sensor devices. A new type employs the electrical load of the SAW device by the impedance of conventional sensors. In order to develop a wirelessly interrogable magnetic field sensor, the combination of GMI sensors and SAW transponders is discussed by several measurements. The device shows a relative signal sensitivity of 80 dB/T at low magnetic flux density B<30 mT, quick response (/spl ges/40 MHz bandwidth), and a high-temperature stability.

Theory and application of passive SAW radio transponders as sensors

Surface acoustic wave (SAW) radio transponders make it possible to read identification codes or measurement values from a remote location. The decisive advantage of these SAW transponders lies in their passive operation (i.e., no power-supply), and in the possibility of wireless installation at particularly inaccessible locations. The passive SAW transponders are maintenance free. Identification marks respond to an interrogation signal with their nonchanging identification pattern. In wireless SAW sensors the physical or chemical properties to be detected change the propagation characteristics of the SAW. SAW radio transponders are advantageously placed on moving or rotating parts and in hazardous environments such as contaminated or high voltage areas. They also can be used for contactless measurements in high vacuum process chambers, under concrete, extreme heat, or strong radioactive radiation, where the use of conventional sensors is complicated, dangerous, or expensive. In this paper we discuss the principles of wireless passive SAW transponders and present a radio frequency interrogation unit and several passive radio SAW sensors developed for noncontact measurements of temperatures, pressures, torques, and currents.

Inductive antenna coupling for a surface acoustic wave transponder

An arrangement is disclosed for coupling electrical energy into and/or out of a surface acoustic wave (SAW) device, such as a transponder. The SAW device has two input/output terminals electrically connected to at least one transducer for converting between electrical energy and SAW energy. Such transducer presents to the terminals a prescribed capacitance in the frequency range of operation. An inductive loop, formed by at least one turn of an electrical conductor, is connected to the two input/output terminals of the SAW device. The inductance of the loop is made substantially equal to the prescribed capacitance at the frequency range of operation, thus forming a resonant circuit with the SAW device. The loop also forms a protective DC short circuit across the two terminals, preventing build-up of static electricity. The inductive loop is inductively coupled to an antenna capable of receiving and/or transmitting radiation in the frequency range of operation.