Design methodology for Class D ultrasound transducer drivers

Abstract

Ultrasound refers to sound waves with frequencies above the upper limit of human hearing. Due to the high frequency, the energy can be concentrated and used for therapeutic applications, such as ultrasound imaging and therapeutic devices. This thesis focuses on the design of driving circuits for ultrasound transducers. The Class D amplifier loaded with a piezoelectric ultrasound transducer is analyzed, and a design methodology is developed. The resulting design achieves high efficiency and can handle transducer impedance variations by adjusting two capacitances in the matching network. The amplifier topology is simple and low-cost. If this design is implemented in the lab, it will require a variable DC voltage supply, a gate driver, two NMOSs, an L-C filter, and a parallel capacitor. A reference design to drive disc-shaped transducers with a radius of 20 mm, and a thickness of 2.8 mm, made of piezo-composite crystal, is presented to illustrate the design methodology. The resulting amplifier can provide a power of near 50 W at 1034 kHz with 97 % efficiency when driving six different transducer samples. The analysis and design methodology are validated by simulating the amplifier performance in LTSpice and a corner analysis considering matching network component variations.