Acoustic tunable metamaterials based on anisotropic unit cells

We propose a tunable acoustic metamaterial based on anisotropic elements. By changing the incident angle or rotating the unit cell, the refractive index can be tuned continuously. Such an acoustic metamaterial element can be used to design and fabricate tunable gradient-index lenses, such as fundamental functional lenses, convergent lens, divergent lens, and deflection lens. These functions can be switched in real time without changing the physical structure. A prototype of the acoustic lens is fabricated by using three-dimensional printing technology, and the regulatory mechanism is implemented to testify its versatility. Our finding opens an avenue for designing tunable acoustic metamaterials and is expected to have wide applications in acoustic devices.