Design and experimental analysis of nonreciprocal wave propagation in a space-time modulated beam

Abstract

Breaking reciprocity in wave propagation problems is of great interest within the research community, given the opportunity to design new devices for one-way communication with unprecedent performances. In the context of mechanics and phonon transport, directional wave manipulation can be achieved exploiting space-time periodic materials. Namely, structures whose elastic or physical properties are functions of space and time.In this work we experimentally study nonreciprocal wave propagation in a space-time modulated beam based on piezoelectric actuation. The system is made of an aluminum beam with an array of piezoelectric patches bonded on its top and bottom surface. Each patch is attached to a negative capacitance (NC) shunt driven by switching circuit, which is able to provide a square-wave stiffness profile in time to the layered material. Spatiotemporal modulation is induced by phase shifting the temporal modulation law of three consecutive piezo-elements, generating a traveling Young's modulus that mimics the propagation of a wave along the beam dimension. As a result, we achieved 1kHz directional bandgaps, i.e. bandgaps at different frequencies for counter propagating waves, which can be moved in a range spanning 8-11 kHz.

Omindirectional Non-Reciprocity via 2D Modulated Radial Sonic Crystals

“…Upon substitution of Equations (5) and (6) in Equation 4and exploiting the orthogonality of the exponential functions, an eigenvalue problem can be obtained in the form (see the details in Appendix A):…”

“…Dispersion properties showing lack of mirror symmetry in the wavevector space witness the breaking of such principle, implying directional propagation characteristics. The breaking of reciprocity is considered an interesting topic within the research community and is motivated by numerous applications of technological relevance for different realms of physics, such as mechanical [1][2][3][4][5][6], acoustic [7][8][9], and electromagnetic [10] systems. In this context, one dimensional space-time modulations have been successfully conceived to generate filtering bands (or bandgaps ) occurring at different frequencies for counter propagating waves.…”