  In this paper, we present the design and experimental validation of a
labyrinthine metamaterial for vibro-acoustic applications. Based on a 2D unit
cell, different designs of finite-size metamaterial specimens in a sandwich
configuration including two plates are proposed. The design phase includes an
optimisation based on Bloch-Floquet analysis with the aims of maximising the
band gap and extruding the specimens in the third dimension while keeping the
absorption properties almost unaffected. By manufacturing and experimentally
testing finite-sized specimens, we assess their capacity to mitigate vibrations
in vibro-impact tests. The experiments confirm a band gap in the low- to
mid-frequency range. Numerical models are employed to validate the experiments
and to examine additional vibro-acoustic load cases. The metamaterial's
performances are compared to benchmark solutions, usually employed for noise
and vibration mitigation, showing a comparable efficacy in the band gap region.
To eventually improve the metamaterial's performance, we optimise its
interaction with the air and test different types of connections between the
metamaterial and the homogeneous plates. This finally leads to metamaterial
samples largely exceeding the benchmark performances in the band gap region and
reveal the potential of interfaces for performance optimisation of composed
structures.
