A mechanical vibration sensing technique using a liquid delay line oscillator

A technique for measuring mechanical vibration displacement is proposed using a liquid-delay-line-oscillator, which is composed of two pairs of arch-shaped interdigital transducers (IDTs) on a double-layered substrate composed of a piezoelectric ceramic plate and an acrylic plate, a polymer-film diaphragm as one wall of a liquid cavity, and a water layer. The diaphragm functions as an ultrasound-beam reflector. The acoustical phase change arises corresponding to the pressure exerted on the central part of the diaphragm. The relationship between the mechanical displacement and the oscillation frequency is evaluated experimentally on the basis of the acoustical delay length linearly dependent on the thickness of the water layer. The static and dynamic displacement measurements are demonstrated. The present technique is promising for sensing sound pressure, which could be regarded as a precise and convenient method.