Acoustic black hole ultrasonic radiator for high-efficiency radiation

The utilization of conventional longitudinal transducers in the field of ultrasonic liquid processing is constrained by limitations in radiation area and directional characteristics. These limitations can be addressed through the implementation of mode conversion techniques. However, an expanded radiation area may also result in reduced acoustic radiation intensity. To mitigate this issue, this study proposes an Acoustic Black Hole Ultrasonic Radiator (ABHUR) designed to enhance ultrasound intensity and thereby achieve high-efficiency radiation. The proposed ABHUR comprises a Bolted Langevin-type Transducer (BLT) and a Curved Acoustic Black Hole (CABH) ring. A theoretical model, based on the transfer matrix method, is developed to analyze the in-plane vibrational behavior of the CABH ring, and its validity is confirmed through Finite Element Method (FEM) simulations. The underwater vibrational and sound field distribution properties of the ABHUR are investigated using FEM and compared with two alternative radiators employing longitudinal-bending (L-B) and longitudinal-radial (L-R) modes. Owing to the unique properties of the Acoustic Black Hole structure (ABHs), which amplify bending wave amplitudes and concentrate energy, the ABHUR operating in L-B mode demonstrates superior ultrasound intensity. Furthermore, a prototype of the ABHUR is fabricated, and a series of three experiments are conducted to validate the operational feasibility of the proposed system.