Non-Hermitian elastic waveguides with piezoelectric feedback actuation: non-reciprocal bands and skin modes

TL;DR

This paper explores non-Hermitian elastic waveguides with piezoelectric feedback, revealing non-reciprocal wave behavior, skin modes, and band splitting, advancing the design of metamaterials for vibration control and wave manipulation.

Contribution

It introduces a spectral model demonstrating non-reciprocal dispersion and skin modes in piezoelectric feedback-controlled waveguides, highlighting effects of feedback sign and non-locality.

Findings

Switching feedback sign inverts wave amplification direction.

Increasing non-locality splits pass bands into multiple non-reciprocal bands.

Skin modes are predicted by the winding number of complex dispersion bands.

Abstract

In this work, we investigate non-Hermitian elastic waveguides with periodically applied proportional feedback efforts, implemented through piezoelectric sensors and actuators. Using onedimensional spectral models for longitudinal motion, it is shown that dispersion diagrams of this family of structures exhibit non-reciprocal imaginary frequency components, manifesting as wave attenuation or amplification along opposite directions for all pass bands. The effects of positive and negative proportional feedback, as well as local and non-local actuation are investigated. Overall, switching the sign of the feedback effort inverts the amplification direction, while increasing the degree of non-locality produces splitting of the pass bands into multiple bands with interchanging non-reciprocal behavior. Furthermore, skin modes localized at the boundaries of finite domains are investigated and successfully predicted by the winding number of the complex dispersion bands. These results contribute to recent efforts in designing metamaterials with novel properties associated with the physics of non-Hermitian systems, which may find fruitful technological applications relying on vibration and noise control, wave localization, filtering and multiplexing.