Zero reflections by a 1D Acoustic Black Hole termination using thermally controlled damping

The design of lightweight and stiff structures with attractive vibration damping properties is a major issue in mechanical engineering. The insertion of Acoustic Black Holes (ABH) in a beam is a technique that consists in locally reducing its thickness at the end and coating it with a visco-elastic film. The reflection coefficient of the resulting system decreases with frequency and displays typical arches which can exactly reach zero when the amount of losses is well adjusted, reaching the critical coupling condition. However, the precise amount of added damping is very difficult to tune by using classical visco-elastic layers. It is here proposed to control it by using a thermal active system acting in a shape memory polymer (SMP). In this manner, the damping and stiffness profiles become tunable via a given thermal gradient which leads to create an enhanced ABH (eABH) that can be tuned in real time, so that the critical coupling can be reached. The objective of the paper is to demonstrate numerically and experimentally the capability of an eABH to achieve exact zero reflections using precise control of temperature gradients.