Bidirectional Acoustic Negative Refraction Based on a Pair of Identical Purely Imaginary Metamaterials Slabs

Abstract

Acoustic purely imaginary metamaterials (PIMs) slabs can support the coexistence of coherent perfect absorption and laser modes and are used to achieve negative refraction. Previous works have focused on a pair of different PIM slabs, one operating in CPA mode and the other in laser mode. However, this structure has restrictions on the incident wave direction, specifically the wave can only be incident from the CPA side. In this paper, we derive the analytical expressions for the parameters required for the coexistence of CPA and laser modes in acoustic PIM slabs. Numerical simulation results show that such PIM slab can freely switch states between the coherent complete absorber and the laser depending on the incidence direction. On this basis, by using a pair of identical PIM slabs, bidirectional negative refraction and planar focusing can be achieved. In addition, the parameters in the appropriate range can be found by adjusting the mode order, which facilitates the experimental verification. So far, the required acoustic purely imaginary metamaterials (PIMs) have not been experimentally demonstrated, and the results presented in the manuscript are theoretical speculations on their existence, so practical applications may require more sophisticated design and engineering.