Experimental Demonstration of an Acoustic Asymmetric Diffraction Grating Based on Passive Parity-Time-Symmetric Medium

A passive parity-time (PT) symmetric medium provides a feasible scheme to experimentally investigate non-Hermitian systems. We experimentally demonstrate an acoustic asymmetric diffraction grating based on a designed passive PT-symmetric medium. The proposed passive PT-symmetric medium is composed of additional cavities and leaked holes. By skillfully combining these two unit cells, the composite unit cell can simultaneously modulate the real and imaginary parts of the refractive index. When the modulation amplitudes of the real and imaginary parts are equal, asymmetric diffraction is observed in both simulated and experimental results at an exceptional point. Compared to the previous design method of a passive PT-symmetric medium, the proposed scheme could prevent the influence of interferential diffraction beams and enhance the diffraction ability with more compact modulation. In addition, the designed metamaterial structure provides a practical way to construct passive PT-symmetric acoustic potential and opens alternative possibilities for further investigation of acoustic wave control in non-Hermitian systems.