Virtual acoustic black holes as a means to achieve low-frequency vibration reduction

Acoustic black holes (ABH) offer exceptional broadband vibration capabilities but have the inherent drawback of being only effective beyond a specific cut-on frequency. The most straightforward approach to set this threshold to a low value is to increase the ABH length. However, such a strategy leads to a very thin tip of the ABH, making it very complicated if not impossible to manufacture. Improving this ABH property has been for the past decade an active field of research. Recently, the concept of a virtual acoustic black (VABH) has been proposed by the authors. The key idea of this approach is to implement digitally the mechanical impedance of the ABH. The virtual feature of this strategy enables the implementation of any kind of ABH (any dimensions, material). Setting the cut-on frequency to low values thus becomes possible. The VABH is implemented through the use of piezoelectric patches, making it very compact and autonomous. Experimental demonstration shows that the proposed idea is able to mitigate vibration below 100 Hz.