Underwater Directional Acoustic Source Based on Pentamode Material

An underwater directional acoustic emitter is conceived with a highly anisotropic lattice material, whose acoustic characteristics manifest strong dependence on the orientation of the lattice material’s principal axis. Exploiting these features, a cylindrical structure made of such anisotropic lattice material is engineered to possess distinct impedance values in different directions, thereby facilitating wave emission along the principal axis while inducing reflection in other directions. Notably, through numerical simulations, it is demonstrated that the emission direction can be effectively manipulated by adjusting the principal axis orientation, concurrently enhancing the emitted power. In contrast to previous directional acoustic structures, the compact emitter presented in this study can get rid of the size-wavelength constraint, enabling effective control of low-frequency waves.