Influence of dielectric losses on the shift of the fundamental frequencies of thickness mode piezoelectric ceramic resonators

Abstract The influence of dielectric losses on the shifts of the characteristic frequencies f s and f p , defined as the frequencies of maximum electrical conductance and resistance respectively, is investigated at the fundamental resonance bands of thickness extensional piezoelectric ceramic resonators. The more general expression for the complex electrical input impedance is used as a reference instead of the usual Butterworth–Van Dyke equivalent circuit. The concept of normalised electrical impedance of the lossy resonator is introduced and applied to the computation of the departs of the characteristic frequencies f s and f p , from the associated lossless critical frequencies f 1 and f 2 , as a function of k t , tan δ m , and tan δ e . It is shown that, according to the adopted model, the effects of dielectric losses on the critical frequencies are different than those produced by mechanical losses: on the one hand, intrinsic mechanical losses increase f s and lower f p ; on the other hand, dielectric losses lower f s and augment the decrease of f p . The frequency displacements have been computed over a wide range of the fundamentals parameters, which include typical values of ceramic materials used for ultrasonic imaging applications.