ANALYSIS OF COMPRESSIONAL-WAVE INFLUENCE ON THICKNESS-SHEAR-MODE RESONATORS IN LIQUIDS

The operation of a thickness-shear-mode (TSM) resonator contacting a f inite liquid layer has been analysed to investigate the effect of comp ressional-wave generation. This effect is mainly related to the non-un iform shear velocity profile across the surface of a TSM device, Hydro phone measurements show two coils of longitudinal waves. Their influen ce on the TSM resonator response is studied with impedance analysis, v arying the spacing between resonator and reflector as well as the refl ecting conditions on the top side of the liquid layer. A characteristi c response with a periodicity of lambda/2 is observed when the spacing of the liquid cavity or the liquid layer thickness is changed. It ind icates standing longitudinal waves in the cavity. Their influence can be modelled with an additional complex impedance in the motional arm o f the Butterworth-van-Dyke equivalent circuit representing an own (com pressional) transmission line.