Theoretical and Experimental Investigation of Ultrasonic Transducers With Dual Oppositely Polarized PMN-PT Layers in Wide Frequency Range

Abstract

The electrical and acoustic characteristics of a two-layered piezoelectric transducer in a broad frequency range are investigated. The theoretical modeling of the transducer having dual oppositely polarized lead magnesium–lead titanate (PMN-PT) layers based upon KLM equivalent circuit theory with the complex piezoelectric material constants is reported. The complex material constants of the piezoelectric single crystal including the frequency-dependent loss properties are obtained by fitting the measured electrical impedance resonance characteristics. The electrical impedance and surface vibration displacement characteristics at frequencies up to the third harmonic of the two-layered piezoelectric transducers with various layer thicknesses are studied by simulation and measurement. It is found that the nonuniformity of the two active layer thicknesses promotes the second harmonic of the electrical and acoustic frequency characteristics, which can be optimized to extend the bandwidth of multilayer piezoelectric transducers. The reported model with the complex piezoelectric material constants can predict the electrical impedance of the multilayer piezoelectric transducers with the agreement functions above 69% and the characteristic frequency errors below 3.03% over the frequency range covering the first three harmonics. The predicted harmonic frequency errors of the acoustic output are less than 6.8%. This work fundamentally supports the design and optimization improvement of multilayer piezoelectric ultrasonic transducers for wide frequency range applications.