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