A longitudinal-flexural ultrasonic transducer with acoustic black hole disk for generating intense airborne acoustic...

Longitudinal-flexural ultrasonic transducers (LFUTs) are extensively used in processing and manufacturing industries owing to their advantages of high efficiency, large areas, high power capacity, and controllable modes. With the rapid advancement of industrial technology, enhancing the performance of the air-coupled ultrasonic transducers has become increasingly critical for ultrasonic processing applications. Consequently, developing new LFUTs to improve acoustic radiation efficiency holds significant importance. In this paper, we introduce a novel LFUT featuring an acoustic black hole (ABH) cross-sectional profile radiation disk (ABH-disk) designed to enhance its radiation efficiency. The ABH effect reduces the velocity of flexural wave, thereby modulating and amplifying the displacement amplitude on the radiating surface. To rapidly optimize the acoustic black hole longitudinal-flexural ultrasonic transducer (ABH-LFUT) design, a theoretical analysis method capable of accurately calculating the resonance frequency of arbitrary function surface contour disks was established. The ABH-disk exhibits superior performance in vibration and radiation characteristics. Compared to radiation disks with other profiles, it achieves higher electroacoustic efficiency and air-coupling equivalent acoustic transmission coefficient under identical frequencies. In actual measurement, the vibration displacement amplitude of the ABH-LFUT is more uniform and substantially larger than that of the flat longitudinal-flexural ultrasonic transducer (F-LFUT). Moreover, the far-field acoustic pressure produced by the ABH-LFUT exceeds that of the F-LFUT, with the peak acoustic pressure being approximately twice as high. These findings demonstrate that the ABH design significantly enhances the radiation capability of LFUTs. This research provides a new direction for the miniaturized design of high-performance LFUT.