Design and performance investigation of a novel spherically-capped ultrasonic focusing transducer

To enhance the far-field local sound pressure of ultrasonic transducers for liquid processing, a novel 48 kHz ultrasonic spherical-cap focusing transducer structure is proposed in this study. The structure arranges five sets of piezoelectric ceramic stacks uniformly on the spherical-cap surface of the front cover plate. Based on acoustics field theory, the primary structural and operational parameters were determined, and COMSOL simulations were used to analyze the resonance frequency and sound field characteristics. After fabricating the focusing transducer, impedance characteristics, torque assembly experiments, amplitude characteristics tests, sound intensity tests under liquid load and aluminum foil erosion verification tests were performed. The results show that, under a 21 N·m assembly torque and a 270 V sinusoidal voltage excitation, the resonance frequency is 47.825 kHz, and the displacement at the center of the front cover plate’s bottom surface is approximately 4.25 µm. Additionally, under water load, the theoretical focal point’s sound intensity is 0.6 W/cm². By comparing the amplitude, sound intensity at other specific points, and the surface phenomena of the aluminum foil, it was verified that the effective focusing region of this spherically-capped transducers is a spherical domain with a radius of 5 mm centered at the theoretical focal point. This study provides a novel structural reference for high-power liquid-processing ultrasonic focusing transducers.