Power amplifier for ultrasonic transducer excitation

Abstract

Design of the power amplifier for ultrasonic transducer excitation is presented. We assumed that the amplifier output impedance will be significantly lower than the transducer input impedance. Therefore we suggest using the transformer as voltage step-up and impedance matching element. The transformer influence on the ultrasonic transducer bandwidth and power transfer efficiency is analyzed using Butterworth-Van Dyke transducer model. The transformer magnetizing and leakage inductance influence on particular air coupled transducer are investigated by modelling and experimentally. The transformer application allows using the same carrier type (n-p-n bipolar or n-channel MOSFET) active elements in push-pull configuration at the amplifier output stage. The commercially available relatively low voltage MOSFET is suggested. Two types of MOSFET transistors are investigated. The resulting amplifier performance has been investigated. The 50kHz to 3MHz bandwidth is obtained for the suggested amplifier configuration. The distortion and efficiency performance are investigated experimentally and using the P-SPICE modelling over various input signals range. The total harmonic distortion of 4% using 3kW load and 400Vp-p 1MHz frequency signal is achieved. The investigation indicate the ability to use such a power amplifier for arbitrary waveform or high power continuous waveform excitation of the ultrasonic transducer.