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Monday, July 8 • 16:30 - 16:50

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An acoustic metamaterial sound-insulator by Helmholtz resonators combined with thin membranes is developed to realize extraordinary sound transmission loss (STL). Small Helmholtz resonators are embedded periodically within the sub-wavelength throughout the insulation plate that covers an elastic plate with an intermediate air layer to compose a double-wall system. The throats of the Helmholtz resonator open at the intermediate air layer, and the bottom faces of the back cavities are composed of thin membranes. This system has three resonances; One is a structural resonance of a mass and spring system where the insulation plate works as a mass and the intermediate air layer as a spring. Second one is an acoustic resonance of the Helmholtz resonator. The last one is an elastic resonance of the membrane at the bottom surface of the back cavity. This system exhibits extraordinary high STL compared with a conventional double-wall insulation system in the frequency range where these three resonances are excited. This frequency range can be controlled by designing the geometry of the Helmholtz resonators, the intermediate air layer, and the size and the stiffness of the thin membrane. The theoretical analysis gives the expression of the equivalent properties of the intermediate air layer and the insulation plate. Numerical calculations are also performed by using representative unit cell. To demonstrate the acoustic performance of the developed system, an elastic steel plate of 1 mm is covered with a plastic plate of 20 mm thick where the resonators that has a resonance around 1.6 kHz. Air layer of 5 mm between these two plates gives resonant transmission loss around 800 Hz, and the membrane of 0.1mm thickness gives an elastic resonance around 2.2 kHz. The finite element analysis utilizing COMSOL Multiphysics gives higher transmission loss than a conventional double-wall from 1 kHz to 2 kHz.

Monday July 8, 2019 16:30 - 16:50 EDT
St-Laurent 5
  T08 Mat. for noise & vibr. cntrl., SS03 Ac metamtrl & phon crstl: fund & app