Tunable Unidirectional Sound Propagation through a Sonic-Crystal-Based Acoustic Diode

TLDR

Nonreciprocal wave propagation usually requires strong nonlinear materials to break time‑reversal symmetry. The diode’s nonreciprocity arises from mode transitions and differing energy conversion efficiencies across diffraction orders on its two sides. The sonic‑crystal acoustic diode delivers controllable, high‑efficiency, broadband unidirectional sound transmission by rotating its rods, providing a low‑power alternative to nonlinear nonreciprocity.

Abstract

Nonreciprocal wave propagation typically requires strong nonlinear materials to break time reversal symmetry. Here, we utilized a sonic-crystal-based acoustic diode that had broken spatial inversion symmetry and experimentally realized sound unidirectional transmission in this acoustic diode. These novel phenomena are attributed to different mode transitions as well as their associated different energy conversion efficiencies among different diffraction orders at two sides of the diode. This nonreciprocal sound transmission could be systematically controlled by simply mechanically rotating the square rods of the sonic crystal. Different from nonreciprocity due to the nonlinear acoustic effect and broken time reversal symmetry, this new model leads to a one-way effect with higher efficiency, broader bandwidth, and much less power consumption, showing promising applications in various sound devices.