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.
Tan et al. (Tue,) studied this question.