Manipulation for Asymmetric Wave Reflection in Space–Time Modulated Media With Exceptional Points

Abstract

Manipulation for asymmetric wave reflection based on exceptional points (EPs) is studied systematically in elastic media with the space–time modulated stiffness, density, and the simultaneous modulation of them. A theoretical formulation for calculating the band dispersion of modulated media and wave scattering response of finite media is developed. Comparison analyses of dispersion and scattering performances are conducted to disclose the connection of non-Hermitian EPs with asymmetric wave reflection for each medium system. The stiffness-modulated medium supports a pair of asymmetric EPs, while one EP can be activated due to its coalescing eigenvector feature to produce asymmetric reflection of the low-order mode. Apart from possessing this behavior, the density-modulated medium can produce an additional EP-induced asymmetric reflection relevant to the high-order mode. The simultaneous space–time modulation of the stiffness and density can realize the reinforcement effect for asymmetric reflection of the low-order mode or produce the cancellation effect to close the low-order mode-related EP such that asymmetric reflection appears only for the high-order mode.