Vibration analysis and optimization design of the low frequency directional flextensional transducer

The size of a flextensional transducer is much smaller than the wavelength, which hinders the ability of compact underwater acoustic transducers to generate directional beams. This paper proposes a directional flextensional transducer that achieves low-frequency directional emission using a single-circuit oscillator driven a spherical concave-convex composite shell. Compared to the traditional methods of using acoustic baffles or the multi-circuit driving that requires amplitude and phase modulation, the transducer designed in this paper only requires a single set of matched power amplifiers, which reduces both cost and installation space. In order to better elucidate the operating principles of low-frequency directional flextensional transducers and guide the design of such transducers, a mathematical model (MM) of the transducer’s vibration is established, and exact solutions are provided. This allows for precise control of the first and second modes of the transducer, enabling the superposition of monopole and dipole modes to form directivity. An optimized design of the transducer is carried out in conjunction with finite element model (FEM), and a prototype transducer is fabricated. The MM, FEM, and experimental (EXP) results exhibit good consistency, verifying the reliability of the design. The fabricated transducer prototype can generate a cardioid directional beam with a back-radiation suppression of up to −9.5 dB in the low-frequency range where ka < 1. This provides a more convenient method for low-frequency underwater acoustic directional transmission.