Ring-excited unimorph ultrasonic transducer with double acoustic black hole structure for enhanced vibration radiation

Abstract

Unimorph ultrasonic transducers have been widely utilized in various ultrasonic applications, owing to their numerous advantages such as a broad operational frequency range, low driving voltage requirements, high electro-mechanical conversion efficiency, compact size, adaptable application conditions, and rapid high-frequency response. As ultrasonic technology continues to advance rapidly, enhancing the acoustic matching and radiation performance of ultrasonic radiators has become increasingly important. To address this need, this study proposes a novel ring-excited unimorph ultrasonic transducer (RUUT) incorporating a double acoustic black hole (DABH) profile to cooperatively improve acoustic radiation efficiency. The inner and outer ABH effects effectively reduce the velocity of flexural waves, modulate and amplify displacement amplitudes on the radiation surface, and enhance the acoustic impedance matching between the transducer and the surrounding air medium. To facilitate the rapid optimization of the transducer design, a theoretical analytical method was developed to accurately calculate the resonant frequency of a disk with an arbitrary surface profile. Experimental results demonstrate that under identical working frequencies, radiation areas, and vibration modes, the DABH-RUUT achieves a maximum vibration displacement twice that of conventional flat-RUUT (F-RUUT). Additionally, it exhibits lower equivalent electrical impedance; higher electro-acoustic efficiency; improved acoustic intensity transmission coefficient; superior air matching performance; and enhanced radiation capability resulting in stronger acoustic pressure. These findings confirm that the DABH design significantly improves air coupling and radiation efficiency of RUUT. This research offers a promising new direction for optimizing the performance of such transducers.