Frequency response of an underwater acoustic focusing composite lens

Abstract Acoustic lenses composed of metamaterials are used as highly anisotropic subwavelength media and have broad applications in a wide range of industrial areas. As reported in recent research, an acoustic lens composed of a cross-shaped structure can achieve high-intensity 3D focusing in an underwater system. However, the operating characteristics of this lens at different frequencies have not been studied in detail until now. In this work, we studied the focusing performance of a particular acoustic lens at different working frequencies, and the band structure, wave intensity distribution, reflection and transmission coefficients, and refractive index of a unit cell were investigated, as well as the characteristics of the acoustic lens through a simulation and experiment. Errors were minimized in the experiments through reasonable design, and we found that although the wave intensity of a single unit cell decreased as the frequency increased, in the acoustic lens, the intensity of the sound field at its focal point increased with the frequency. The present research provides an improved method for designing acoustic lenses with different working frequencies and can guide nondestructive testing (NDT) and biomedical treatment.