Active control of an acoustic black hole using a feedback strategy

Acoustic black holes (ABHs) are tapered structural features that can achieve high levels of structural damping within lightweight constraints. It has previously been proposed to integrate feedforward active vibration control into an ABH to enable control over a broad spectrum, however, the time-advanced information required in this control strategy is not always available. In addition, it has been shown that controlling the reflection coefficient in a beam-based ABH leads to an undesirable enhancement of the taper vibration. In this paper, a feedback control strategy is applied to an ABH terminated beam, with a piezoelectric patch providing the control actuation. The feedback strategy is a remote vibration control methodology and is used to examine the different compensators that are potentially available to control simultaneously both the local taper vibration and the reflected wave component. The investigation highlights that the taper vibration can be minimised without affecting the reflected wave, however, apart from a few isolated frequencies, it is shown that the reflected wave cannot be minimised without increasing the taper vibration relative to the passive case. Importantly, since the approach enables the passive ABH performance to be maintained whilst simultaneously minimising the vibration in the tip, the fatigue life of the structure can potentially be extended with the addition of the active control loop.