Exceptional Points and Skin Modes in Non-Hermitian Metabeams

We present a non-Hermitian metabeam exhibiting an exceptional point (EP) induced by enforcing parity-time (PT) symmetry through applied external forces. The EP is formed by the hybridization of two flexural wave modes and its output displacement is enhanced by attaching two pillars on top of the beam. The introduction of a tiny mass perturbation that breaks the PT symmetry leads to a splitting of the eigenfrequencies at the EP with a square-root dependence on the perturbation mass. This effect manifests itself in a splitting of resonant peaks in the frequency response. The enhanced sensitivity of the EP paves the way to the detection of small perturbations such as tiny masses and cracks. Another property of the metabeam is the existence of skin modes whose energies are localized at one end of the beam and can be generated by implementing nonreciprocal feedback interactions between the pillars. We demonstrate that the skin modes are broadband and independent of the excitation positions. From a practical perspective, we show the great potential of skin modes in broadband energy harvesting. Our study proposes approaches to manipulate the non-Hermitian elastic wave phenomena, paving the way for the development of highly sensitive sensors, vibration control, and energy harvesting.