The application of Surface Acoustic Wave (SAW) resonators as sensor elements for different physical parameters such as temperature, pressure and force is well known since several years. The energy storage in the surface acoustic wave and the direct conversion from physical parameter to a parameter of the wave such as frequency or phase enables the construction of a passive sensor that can be interrogated wireless.
The article presents a temperature measurement system based on passive wireless SAW sensors. The principle of SAW sensors and SAW sensor interrogation is discussed briefly. A new measurement device developed for analyzing the sensor signals is shown. Compared to former interrogation units that detect resonance frequency of the SAW resonator by comparing amplitudes of sensor response signals related to different stimulating frequencies the new equipment is able to measure the resonance frequency directly by calculating a Fourier transformation of the resonator response signal. Measurement results of a field test are presented and discussed.