I. Introduction
High overtone bulk acoustic resonator HBAR is an electroacoustic device in which a piezoelectric thin layer, sandwiched between two electrodes, excite an acoustic wave in a high quality and low acoustic loss substrate, on which it's deposited. When the substrate is thicker than the deposited guiding layer, that is considered as a transducer, the generated acoustic wave propagates in the substrate and form stationary waves between surfaces at the top and the bottom of the substrate. The detected stationary waves from electrodes form frequency equidistant pulses (cardiogram like signal).