Experimental Observation of Nonreciprocal Band Gaps in a Space-Time-Modulated Beam Using a Shunted Piezoelectric Array

In this work, we experimentally achieve 1-kHz-wide directional band gaps for elastic waves spanning a frequency range from approximately 8 to 11 kHz. One-way propagation is induced by way of a periodic waveguide consisting of an aluminum beam partially covered by a tightly packed array of piezoelectric patches. The patches are connected to shunt circuits, where switches allow a periodic modulation in time of the beam properties. A traveling stiffness profile is imposed by phasing the modulation of each active element, inducing the propagation of a plane wave along the material and establishing unidirectional wave propagation at band-gap frequencies.