Broadband non-reciprocal wave suppression and frequency conversion by active metabeams

Non-reciprocal wave propagation has recently attracted considerable attention as it is potentially beneficial to many applications, ranging from waveguiding, sensing, and communication to vibration control. Here, we propose the design of an active metabeam for broadband non-reciprocal wave suppression, that can strongly suppress the transmitted wave for forward incidence and amplify the transmitted wave for backward incidence. The metabeam consists of piezoelectric sensors and actuators connected by a feedforward control loop. We find that the broadband nonreciprocal wave suppression can be realized by making the second forward transmission dip close to the first one, which can be controlled by the distance between the piezoelectric actuators. The broadband non-reciprocal wave suppression of the metabeam is demonstrated via a set of time domain analyses. We further study the frequency conversion effects of the metabeam based on a time-varying transfer function. In particular, we show that among the frequency converted harmonics, those at high frequencies can be eliminated by destructive interference, resulting in an approximate single-frequency conversion in the transmitted wave. Our study advances the field of non-reciprocal mechanics and offers a reliable platform for designing active broadband elastic wave devices, providing a feasible way for asymmetrical energy control, broadband vibration attenuation, and signal processing.