Theory and application of passive SAW radio transponders as sensors

Abstract

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.

A Novel Chipless RFID System Based on Planar Multiresonators for Barcode Replacement

“…Even with the tags simplicity (antenna and integrated circuit) the modern RFID tag cannot compete with its older brother -the barcode, in terms of price. That's why researchers and engineers have turned towards [7]- [9]. We present a novel chipless RFID system which uses frequency signatures for data encoding.…”

Ultrasonic Coupled Passive Wireless Oscillating Sensor System

“…Similar to wireless passive sensing using surface acoustic wave devices coupled to antennas [4], the approach presented here is based on a time domain separation of the transmitted and reflected signal. The wireless sensor system contains an excitation and receiving element with signal processing on the active part and a transceiver with an oscillating load on the passive sensor-node.…”

Feasibility Study of Surface Acoustic Wave RFID for Information Processing Asset Management

“…In [23], [24] it has been shown, that classical sensors with a varying impedance can be read-out wirelessly, when combined with SAW transponders. For this application, an IDT is used as a reflector, which is loaded by the external sensors.…”