Experimental realization of tunable exceptional points in a resonant non-Hermitian piezoelectrically coupled waveguide

This Letter presents an experimental demonstration of tunable exceptional points (EPs) in an electromechanical waveguide. EPs are non-Hermitian singularities typically found in parity-time (PT) symmetric systems with balanced gain and loss. Here, piezoelectric transducers on an aluminum beam (waveguide) are shunted to synthetic impedance circuits that emulate negative and positive resistors (responsible for gain and loss) and inductors (for resonant tunability), whose properties can be programmed digitally. Specifically, an electrical mode is introduced via inductive shunts to electromechanically interact with target structural mode(s) to create degeneracy. While the internal structural damping of the waveguide has the effect of breaking PT symmetry inherently, we show that EPs can still be created by using non-trivial gain and loss combinations. The results in this Letter pave the way for practical realization of EPs in elastic media toward their application in enhanced sensing and asymmetric wave control, among others.