Displacement measurement by SAW delay-line oscillator consisting of two LiNbO3 plates with IDT

A displacement sensor can be made by constructing a surface acoustic wave (SAW) delay-line oscillator, in which two LiNbO₃ plates with an interdigital transducer (IDT) on the surface of each plate are conjoined by attaching a part of the propagation surface of one plate to a part of the propagation surface of the other. In the SAW sensor, the oscillation frequency depends on propagation path length of the SAW element, which is changed by moving one of two LiNbO₃ plates of the oscillator. It is shown that SAW displacement sensors with high sensitivity, 300 Hz/μm and 1.0 kHz/μm, were achieved by making IDTs of 6.5 pairs with 0.55-mm pitch and those of 5 pairs with 0.4-mm pitch on the surface of Y-X LiNbO₃ plates, respectively. The mode transition of the SAW delay-line oscillator, which occurred at certain propagation path lengths, was observed by using a spectrum analyzer.