Equivalent circuit representation of Poisson-coupled electroacoustic modes

Mode-coupling phenomena have long been recognized as contributing to the detailed frequency-dependent behavior of electroacoustic materials and structures. Coupled modes have the effect of repelling each other from the positions in frequency space that they would occupy if the coupling interaction were not operative. Today, mode-coupling effects are most often addressed using finite-element analysis methods. This paper reinvestigates the Poisson (modes coupled via shared inertial mass) mode-coupling issue for simple electroacoustic structures from another perspective. Beginning with the piezoelectric equations of state, equivalent-circuit models are developed. These are useful for interpreting standard forms of impedance/admittance spectroscopy data for a variety of practical experimental geometries. The models are applied to measurement data and their usefulness for performance simulations is illustrated.