# A Metamaterial Solution for Soundproofing on Board Ship  
[PERSON]  
1 Engineering and Architecture Department, University of Trieste, 34127 Trieste, Italy; [EMAIL_ADDRESS] (M.B. ); [EMAIL_ADDRESS] (G.R. )2 Phononic Vibes Srtl, 20158 Milano, Italy; [EMAIL_ADDRESS] (S.C.); [EMAIL_ADDRESS] (L.D. )3 Civil and Environmental Engineering, Politecnico di Milano, 20133 Milano, Italy4 Civil and Environmental Engineering, Politecnico di Milano, 20133 Milano, Italy5  
Footnote 1: email: {giada.kyawood@[EMAIL_ADDRESS]}  
[PERSON]  
2 Phononic Vibes Srtl, 20158 Milano, Italy; [EMAIL_ADDRESS] (S.C.); [EMAIL_ADDRESS] (L.D. )3 Civil and Environmental Engineering, Politecnico di Milano, 20133 Milano, Italy5  
Footnote 2: email: {giada.kyawood@[EMAIL_ADDRESS]}  
[PERSON]  
1 Engineering and Architecture Department, University of Trieste, 34127 Trieste, Italy; [EMAIL_ADDRESS] (M.B. ); [EMAIL_ADDRESS] (G.R. )2 Phononic Vibes Srtl, 20158 Milano, Italy; [EMAIL_ADDRESS] (S.C.); [EMAIL_ADDRESS] (L.D. )3 Civil and Environmental Engineering, Politecnico di Milano, 20133 Milano, Italy5  
Footnote 3: email: {[EMAIL_ADDRESS]}  
[PERSON]  
1 Engineering and Architecture Department, University of Trieste, 34127 Trieste, Italy; [EMAIL_ADDRESS] (M.B. ); [EMAIL_ADDRESS] (G.R. )2 Phononic Vibes Srtl, 20158 Milano, Italy; [EMAIL_ADDRESS] (S.C.); [EMAIL_ADDRESS] (L.D. )3 Civil and Environmental Engineering, Politecnico di Milano, 20133 Milano, Italy5  
Footnote 4: email: {[EMAIL_ADDRESS]}  
[PERSON]  
2 Phononic Vibes Srtl, 20158 Milano, Italy; [EMAIL_ADDRESS] (S.C.); [EMAIL_ADDRESS] (L.D. )3 Civil and Environmental Engineering, Politecnico di Milano, 20133 Milano, Italy5  
metamaterials with different characteristic can be layered. These properties make acoustic metamaterials an effective and lightweight solution for noise and vibration proofing [3; 9]. In the aeronautical field, the effect of different metamaterial solutions (i.e., structures composed of primitive cells repeated in space) for the core of sandwich panels has been numerically and theoretically studied [19; 20; 21], as an improvement to the traditional honeycomb core solution from a structural, weight, and STL performance point of view. This involves the repetition in space of different morphologies of lattice structures: pyramidal truss cores [19; 20], two-layered pyramidal truss cores [21], tetrahedral cores [19], and 3D Kagome cores [20]. These types of solutions can be redirected to the MAM and MSM typologies of metamaterials, thus presenting a new solution. This work aims to introduce a novel metamaterial solution (the Metasolution in the following) and a related design approach for noise reduction applications, proposing a new lattice structure for sandwich panels, focusing on the on-board-ship environment with all its regulations and constraints. The target acoustic performance, weight and thickness are set by the traditional solution usually adopted in this sector, composed of two honeycomb aluminum panels and a mineral wool layer. Its STL is determined from the experimental point of view in coupled chambers in the laboratory, using a sound intensity measurement technique. The innovative metamaterial solution is then optimized to exceed the sound insulation performances offered by traditional solutions, reducing the panel thickness while keeping weight and costs constant. The Metasolution is designed using an FEM acoustic-structural numerical model, and the model is validated by comparing the numerically predicted acoustic performances with the performed experimental test. To ensure that the Metasolution is compliant with the safety regulations imposed for materials on board [22], the surface flammability and the spread of flame are also evaluated. In the following sections:  
1. The traditional honeycomb panel solution is presented and characterized experimentally to determine its STL. 2. The description of materials and geometries and the numerical method adopted for the design of the metamaterial solution are shown, together with its predicted performances. 3.