Measurement of vibration displacement using a layered-structure leaky wave interdigital transducer

A technique for measuring vibration displacement using a liquid delay line is described. The delay line is composed of two pairs of layered-structure interdigital transducers (IDTs), in combination with a piezoelectric ceramic thin plate and an acryl plate, and a sound-beam-reflecting diaphragm as one wall of a liquid cavity. The IDT functions as a bulk wave radiator or a detector of a signal reflected from the diaphragm. The acoustic delay length changes linearly with the mechanical displacement of the diaphragm. Basic performances of the liquid delay line and measurement results for vibration displacement are presented.