Nonlinear equivalent circuits of acoustic devices

New definitions of the nonlinear equivalent circuits of a broad plate for thickness-extensional vibration and a thin bar for length-extensional vibration are presented. These are obtained by extending Mason´s linear equivalent circuits to the nonlinear region and are applied to the analysis of the second harmonic generation at the resonance point in the broad plate of Z-cut LiNbO₃ and to the determination of the fourth-order compliance constant of X-cut longitudinal mode quartz crystal resonator by evaluating the resonance frequency difference as a function of current amplitude. The successful result of simulation of the generation of acoustic phase conjugate wave in a lead zirconate titanate (PZT) ceramic thin bar is also presented