Sound Isolation and Giant Linear Nonreciprocity in a Compact Acoustic Circulator

TLDR

Acoustic isolation and nonreciprocal sound transmission are highly desirable, yet conventional approaches rely on nonlinear or magneto‑acoustic effects that require high power and large volumes, whereas nonreciprocal electromagnetic propagation is routinely achieved via Zeeman‑effect or magnetic‑bias modal splitting. The study introduces an acoustic analog of magnetic‑bias nonreciprocity by biasing a subwavelength resonant ring cavity with circulating fluid. By biasing the ring cavity with circulating fluid, angular momentum bias splits azimuthal resonant modes, enabling giant acoustic nonreciprocity in a compact device. The resulting circulator achieved up to 40‑decibel nonreciprocal isolation for airborne sound at audible frequencies.

Abstract

Acoustic isolation and nonreciprocal sound transmission are highly desirable in many practical scenarios. They may be realized with nonlinear or magneto-acoustic effects, but only at the price of high power levels and impractically large volumes. In contrast, nonreciprocal electromagnetic propagation is commonly achieved based on the Zeeman effect, or modal splitting in ferromagnetic atoms induced by a magnetic bias. Here, we introduce the acoustic analog of this phenomenon in a subwavelength meta-atom consisting of a resonant ring cavity biased by a circulating fluid. The resulting angular momentum bias splits the ring's azimuthal resonant modes, producing giant acoustic nonreciprocity in a compact device. We applied this concept to build a linear, magnetic-free circulator for airborne sound waves, observing up to 40-decibel nonreciprocal isolation at audible frequencies.