Asymmetric acoustic energy transport in non-Hermitian metamaterials

One of our studies on linear and nonlinear non-Hermitian metamaterials has been published on the recent special issue of the Journal of the Acoustical Society of America: Non-Reciprocal and Topological Wave Phenomena in Acoustics.

Abstract

The ability to control and direct acoustic energy is essential for many engineering applications such as vibration and noise control, invisibility cloaking, acoustic sensing, energy harvesting, and phononic switching and rectification. The realization of acoustic regulators requires overcoming fundamental challenges inherent to the time-reversal nature of wave equations. Typically, this is achieved by utilizing either a parameter that is odd-symmetric under time-reversal or by introducing passive nonlinearities. The former approach is power consuming while the latter has two major deficiencies: it has high insertion losses and the outgoing signal is harvested in a different frequency than that of the incident wave due to harmonic generation. Here, we adopt a unique approach that exploits spatially distributed linear and nonlinear losses in a fork-shaped resonant metamaterials. Our compact design demonstrates asymmetric acoustic reflectance and transmittance, and acoustic switching. In contrast to previous studies, our non-Hermitian metamaterials exhibit asymmetric transport with high frequency purity of the outgoing signal.

Full article: https://asa.scitation.org/doi/abs/10.1121/1.5114919