Peculiarities of Wireless Interrogation of SAW-Resonator Vibration Sensor by RF Pulse-Signal

Vibration surface acoustic wave (SAW) sensors can be used in multiple areas like automotive and aerospace technologies. Remote wireless interrogation of these passive sensors and their operability at high temperature allows to use them on rotating and moving objects in harsh environments. This work concentrates on peculiarities related to RF-pulse interrogation of a SAW resonator (SAWR) vibration sensor. The analysis describes the vibration-induced continuously-shifting SAWR response resonance frequency by approximating it with a sequence of static frequency responses with different central frequencies that are fixed during each consequent interrogation cycle of excitation/reception intervals. This approach is justified by a relatively small (below 2 ppm) SAWR frequency change during each cycle. The analysis realized in a PC allows to simulate both AM and FM demodulation of arbitrary signals with complicated modulation. This method also gives some insight in understanding of distortions in re-radiated signal at a relatively large vibration magnitude. Modeling of the situation when the deviation of the SAWR sensor resonance frequency exceeds the SAWR response passband explains the observed phenomenon of the re-radiated power decrease. It also gives the explanation of the nature of non-linear features experimentally observed in demodulated signals at large levels of vibration. The described approach will be used for optimization of interrogation procedure.