Low-frequency sonophoresis is a minimally invasive transdermal drug delivery technique and has attracted attention as an alternative to injections. For medical applications, compact transducers capable of emitting low-frequency and high-intensity ultrasound remain a key objective. In our previous studies, we designed a compact low-frequency ultrasound transducer composed of a bowl-shaped acoustic resonator and disk-shaped piezoelectric element. In this work, we proposed an improved transducer design that utilizes cavity resonance to enhance acoustic pressure output and reduce heat generation. The aperture diameter of the bowl-shaped cavity was configured to match the acoustic wavelength, enabling the antinode of the structural resonance to coincide with that of the acoustic standing wave. The electroacoustic performance and cavitation-generation capability of the proposed design were evaluated in comparison with our prior design. Acoustic simulations and pressure measurements confirmed enhanced acoustic pressure at the resonance frequency, while water-temperature measurements under ultrasound exposure demonstrated reduced heat generation. Furthermore, cavitation measurements using scattered acoustic signals, optical imaging, and sonochemiluminescence observations revealed that the proposed transducer produced cavitation distributed over a wider area on the target surface. • A compact low-frequency transducer using cavity resonance was developed. • The design matched the aperture diameter to the acoustic wavelength. • Cavity resonance increased sound pressure and reduced power consumption. • The prototype showed lower cavitation threshold than the previous design. • Sonochemiluminescence confirmed efficient cavitation over the aperture.
Yamamoto et al. (Sat,) studied this question.