Modeling and measurements of lead titanate acoustic transducers for input impedance matching development

Abstract

Lead titanate (PbTiO3) is a popular piezoelectric material for acoustic transducers because of its high electromechanical coupling coefficient. To drive a transducer effectively, its input impedance must match well to the generator output impedance, usually 50Ω. To develop impedance matching technique, an equivalent circuit model is established. PT piezoelectric plates are bonded on bismuth, Lucite and LCP, respectively to form transducers. The input impedance of the transducers is calculated and also measure versus frequency. It is discovered that there are two off-resonant frequencies at which the reactance part of the input impedance is zero, referred to as the zero-crossing frequency. This is possible because of an inherent electrical property of the transducer, the existence of the plate capacitance. The higher zero-crossing frequency is close to the resonant frequency. The input resistance is usually very high. At the lower zero-crossing frequency, the input resistance is close to 50Ω for practical plate sizes. Thus, good impedance matching can be achieved by operating at this frequency. The matching can be fine tuned by adjusting transducer electrode size and controlling the bonding layer thickness. Nearly perfect matching is demonstrated without using any external component. The simulated and measurement response curves versus frequency also show the transducer bandwidth.