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P4I-1 Neutrally Buoyant Band Gap Design for Underwater Applications

A locally resonant sonic material (LRSM) design is considered in two dimensions (2D) for obtaining a neutrally buoyant band gap material in underwater applications. The material is intended to have an overall effective mass density the same as that of water, and to produce bandgaps in the 10kHz region. The design problem is more constrained than a standard LRSM design scenario, in that necessitating an overall desired effective density requires a specific combination of material and geometrical properties, whilst also giving the required bandgap performance using only material properties and dimensions likely to be achievable in practice. A design is described featuring a proposed soft rubber-type layer encasing a Lucite core within a Lucite matrix with has an overall material thickness of 90mm. A -20dB band stop in the transmission coefficient magnitude over approximately the 8-12kHz range is achieved. Results are obtained by simulating the system using AFiDS, a staggered grid Finite Difference Time Domain (FDTD) simulator.