Mechanical displacement measurement using a leaky lamb wave delay line oscillator

A measurement technique for mechanical displacement using a liquid delay line oscillator is described. The delay line is composed of a leaky Lamb wave device with two interdigital transducers (IDTs), a liquid cavity as the propagation medium for an ultrasound beam and an amplifier connected between two IDTs. The IDT for leaky Lamb waves functions as a longitudinal wave radiator or a detector of a reflected ultrasound beam from the surface of a wall in the liquid cavity. The two lowest modes, S-0 and A(0), propagating in a thin piezoelectric ceramic plate are useful for constructing the leaky wave transducer because of high transducer efficiency. The acoustic delay length changes with mechanical displacement, which results in a change of oscillation frequency The basic performance of the delay line oscillator is presented with the results of measurements in two operating modes, S-0 and A(0).