Realizing a tunneling-like phenomenon in nonreciprocal active acoustic metamaterials

We demonstrate a tunneling-like phenomenon recently reported in lattices with nonreciprocal couplings, realized here in an active acoustic metamaterial. The system consists of a waveguide with acoustic actuators and sensors embedded in its walls. Nonreciprocity, leading to asymmetric sound transmission in opposite directions, is created using actuators and sensors operating in a real-time feedback loop process. This nonreciprocal sound transmission is realized in an inner portion of the waveguide, thereby forming an artificial non-Hermitian interface that separates two Hermitian sections. This configuration supports the non-Hermitian skin effect, where modes accumulate at one boundary. In our acoustic implementation, we investigate the propagation of a sound wave along the waveguide as it encounters the artificial interface. While the skin mode accumulation acts as a barrier, inhibiting wave penetration into the interface, under specific conditions, the wave tunnels to the other side, creating a quiet zone within the In our realization the cross-section remains unobstructed, akin to a plain waveguide. This experimental demonstration underscores the applicability of the tunneling phenomenon across different physical systems and its potential applications in acoustic wave control.