Study on the radiation directivity of a ring-excited thin circular plate with a fixed boundary.

Air-coupled transducer with a flat plate structure have many applications in the fields of ground weather observation, ultrasonic defoaming, and directional strong acoustic radiation. In this paper, an analytical equation of the far-field radiation directivity of a fixed boundary ring-excited thin circular plate (RTCP) is deduced using Rayleigh integration method. A finite element model of the RTCP is established, and the relationship between the far-field radiation directivity and the excitation position, excitation area and working frequency is studied by considering the third-order axisymmetric flexural vibration of the RTCP. Computation results show that, for a RTCP, the excitation position has more effect on its radiation directivity. When the plate is excited at the positions between first two nodes, the directivity can be enhanced. When the excitation position is in the trough of the normal displacement curve along radius direction, the side lobes of the radiation directivity of the RTCP are minimized. The area of excitation region has smaller influence on the frequency and radiation directivity of the RTCP. However, working frequency has a great influence on the radiation directivity of the RTCP. When the working frequency is close to the vibration frequency of the circular plate, the sound radiation directivity is the best. A prototype fixed boundary circular plate excited by a longitudinal sandwich transducer was designed and manufactured. For comparison, its finite element model was also setup to simulate its acoustic radiation directivity. Experimental results were found to be in agreement with the theoretical calculations and finite element simulation results.