We present the theoretical and experimental investigation of a piezoelectric metamaterial-based acoustic black hole leveraging programmable shunt circuits. A versatile experimental platform is developed comprising a piezoelectric bimorph beam with 30 unit cells, each with a pair of piezoelectric patches with individually programmable shunt impedance. By varying the impedance applied to each unit cell, the local dispersion properties of the beam can be precisely controlled. In this work, we explore a programmable implementation of an acoustic black hole, in which wave packets are slowed down and compressed in space using a smooth gradient in shunt impedance.
We investigate a metamaterial beam with piezoelectric elements shunted to synthetic impedance circuits to demonstrate elastic wave trapping. We numerically and experimentally demonstrate the so-called rainbow trapping phenomenon, in which elastic waves of different wavelengths are trapped in different regions of the metamaterial beam. Guided by numerical simulations, experiments are performed on a beam with 30 piezoelectric elements with synthetic impedance circuits that have gradually varying inductance. Grading profiles are varied through the digital interface to understand its effect on the wave trapping behavior and conclusions are drawn.