Dynamic nonlinearity in piezoelectric flexural ultrasonic transducers

The flexural ultrasonic transducer is a unimorph device which typically comprises a piezoelectric ceramic bonded to a metallic membrane. It is widely applied in industrial applications for metrology and proximity sensing. However, the electromechanical and dynamic characteristics of this class of transducer have only recently been reported, and the influence of different excitation levels on dynamic nonlinearity remains unclear. Dynamic nonlinearity in high-power piezoelectric ultrasonic transducers is familiar, where the performance or dynamic stability of the transducer can significantly reduce under high amplitudes of excitation. Nonlinearity can manifest as measurable phenomena such as resonance frequency drift, influenced by thermomechanical phenomena or structural constraints. There is relatively little reported science of the dynamic nonlinearity in the vibration response of flexural ultrasonic transducers. This study examines the vibration responses of four flexural ultrasonic transducers, showing the existence of dynamic nonlinearity for increases in excitation voltage. An analytical solution of the governing equations of motion for the flexural ultrasonic transducer is presented which complements the experimental investigation, and suggests a close relationship between material properties and nonlinearity. This research demonstrates a detailed dynamic characterization of the flexural ultrasonic transducer, showing the potential for the optimization of dynamic performance in industrial measurement applications.