Acoustic Black Holes (ABHs) have been demonstrated as an effective and particularly lightweight passive vibration control solution. They are able to achieve a high level of structural damping with a thin layer of concentrated damping material by introducing a reduction in the structural wave speed. This is generally achieved by introducing a geometrical taper into the structure and the performance is maximised with a long taper that reaches a small tip height. This design approach introduces a potential weakness into the structure and, therefore, this paper explores an alternative method of achieving a reduction in the wave speed. Instead of a geometrical taper, the potential of realising the ABH effect using a functionally graded structural feature that can be achieved through multi-material additive manufacturing is investigated. Requirements on the gradient of the material properties are first investigated and then a design optimisation strategy is presented to enable the practical realisation within the constraints of a commercially available multi-material additive manufacturing process.
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