Minimisation of the reflection coefficient in a beam using an active acoustic black hole

Acoustic black holes (ABHs) are commonly realised as structural features that can be used for effective lightweight damping. Passive damping material can be added to the taper to enhance the performance. This paper presents an experimental investigation into a hybrid damping solution consisting of an ABH on one end of a beam with a piezoelectric patch attached to the taper. A wave-based control strategy is presented in which the reflected wave was used as the error signal and, therefore, the reflection from the termination was minimised. In order to assess the performance of an active ABH, wave-based active control was also performed on a beam without an ABH termination. In each control case, the plant model error was equal and the control filter was limited to a practical length. Additionally, the maximum peak-to-peak voltage of the control signal was constrained to be within operating limitations. Wave-based active vibration control was then performed in real-time and the results show that the reflection coefficient was successfully controlled in both cases. It is shown that when the AABH was used, a greater attenuation in the reflection coefficient was achieved at lower frequencies and, furthermore, the active ABH required a lower control effort.