Nonreciprocal transmission of sound in viscous fluid with asymmetric scatterers

TL;DR

This paper demonstrates a passive, linear, and cost-effective method for achieving nonreciprocal sound transmission using viscous fluid effects and asymmetric scatterers, confirmed by experiments and simulations.

Contribution

It introduces a novel approach to nonreciprocal sound transmission exploiting fluid viscosity and structural asymmetry without external energy sources.

Findings

Nonreciprocal ultrasound transmission observed experimentally.

Results align with numerical simulations based on Navier-Stokes equations.

Passive device does not require external power, is robust and inexpensive.

Abstract

Two common concepts of nonreciprocity in sound propagation are based on nonlinear effects [1, 2] and on local circulation of fluid [3, 4]. They originate from two known methods of breaking a time reversal symmetry, that is necessary for observation of nonreciprocal effects. Both concepts require additional devices to be installed with their own power sources. Recently it was demonstrated that acoustical losses may serve as a source of T-symmetry violation, thus leading to nonreciprocity in reflection of sound from gradient-index metasurface [5]. Here, we explore viscosity of fluid as a natural factor of T-symmetry breaking. We report experimental observation of the nonreciprocal transmission of ultrasound through a water-submerged phononic crystal consisting of asymmetric rods. Asymmetry, or broken P-symmetry, is the second necessary factor for nonreciprocity. Experimental results are in agreement with numerical simulations based on the Navier-Stokes equation. This passive nonreciprocal linear device is cheap, robust and does not require an energy source.