Acoustic Amplifying Diode Using Nonreciprocal Willis Coupling

We propose a concept called acoustic amplifying diode combining signal isolation and amplification in a single device. The signal is exponentially amplified in one incident direction with no reflection and is perfectly absorbed in another. The reflection is eliminated from the device in both directions with impedance matching, preventing backscattering to the signal source. Here, we demonstrate the amplifying diode using an active metamaterial with nonreciprocal Willis coupling. We also discuss the situation with the presence of both reciprocal and nonreciprocal Willis couplings for more flexibility in implementation. The coexistence of both amplifier and perfect absorber in opposite incident directions extends the regime of sound isolation and further enables applications in sensing and communication, in which nonreciprocity can play an important role.

Automated summary

We propose a concept called acoustic amplifying diode that combines signal isolation and amplification in a single device. The signal is exponentially amplified in one direction with no reflection and perfectly absorbed in another direction. By using impedance matching, the device eliminates reflection in both directions and prevents backscattering to the signal source. We demonstrate the amplifying diode using an active metamaterial with nonreciprocal Willis coupling, and discuss the flexibility of implementation with the presence of both reciprocal and nonreciprocal couplings.