Power amplifier for ultrasonic transducer excitation

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 the power transfer efficiency are analyzed using the Butterworth-Van Dyke transducer model. The transformer magnetizing and leakage inductance influence on a particular air coupled transducer are investigated by modeling and experimentally. The transformer application allows using the same carrier type (n-p-n bipolar or n-channel MOSFET) active elements in a 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 50 kHz to 3 MHz bandwidth is obtained for the suggested amplifier configuration. The distortion and efficiency performance are investigated experimentally and using the P-SPICE modeling over various input signals ranges. The total harmonic distortion of 4% using 3 kOmega load and 400Vp-p 1MHz frequency signal is achieved. The investigation indicates the ability to use such a power amplifier for arbitrary waveform or high power continuous waveform excitation of ultrasonic transducers.