Investigation of nonlinearity in piezoelectric transducers

Abstract

Hard-type piezoelectric devices usually need to be driven under a high vibration level. However, they exhibit nonlinearity under high stress, which must be taken into account. This study investigates the nonlinear behavior of piezoelectric transducers. The burst-mode method was employed to measure the longitudinal vibration velocity of both hard- and soft-type piezoelectric transducers after excitation by a burst voltage. The vibration velocity decreased rapidly with time. The equivalent mechanical loss and equivalent spring constant were determined using the velocity decay rate and resonance frequency. We found that both could be expressed as quadratic functions of velocity, pointing to nonlinearity in the transducers. Admittance curves of the transducers under high voltage were also measured via a frequency response analyzer. These admittance curves also exhibited nonlinearity, as indicated by the deformation in the curves. Particularly in the case of the hard-type transducer, a jumping phenomenon and an admittance hysteresis between the different sweep directions were observed. A model that incorporated the observed nonlinearity was proposed and used to fit the measured admittance curves. Nonlinear coefficients and force factor were yielded by the curve fitting, which confirmed that the proposed model was effective in describing the nonlinear behavior and in estimating the degree of nonlinearity.