Selective Wave Filtering in Time-Modulated Elastic Metamaterials

We implement periodic stiffness time-modulation in a beam with piezoelectric patches and switchable shunted negative capacitance. The shunted negative capacitance circuits, connected in series with each piezoelectric patch through a switch, soften the structure. By alternatively opening and closing the switch, the beam’s stiffness effectively oscillates periodically between two values. We present a simplified theoretical model of time-periodic beams and describe the occurrence of flat bands in the dispersion diagrams. We show that a narrowband reflection from a time-modulated domain can be obtained for a broadband incident wave, hence qualifying the modulated domain as a single-port system with tunable response. We validate our theoretical findings by comparing time-domain simulations with experimental measurements of transient wavefields through scanning Doppler laser vibrometry.