Lightweight soundproofing membrane acoustic metamaterial for broadband sound insulation

According to the mass law, a dense and thick soundproofing material is generally used to block low-frequency sounds. However, lightweight thin soundproofing materials in the form of metamaterials can also be implemented with high sound transmission loss. In this study, we present a soundproofing comprising a thin membrane coupled with an ultralight membrane-type acoustic metamaterial (MAM). Owing to the vibration in the membrane, the structure-borne acoustic radiation of the soundproofing can be easily tuned, making broadband sound insulation possible. The anti-resonance generated by the membrane and thin plate surface minimizes the response of the radiating surface to the acoustic load. Thus, the dynamic effective density and acoustic impedance become extremely high, whereas the normal displacement of the radiating surface is almost zero. We numerically and experimentally demonstrated an open-field test for a plate-type and an enclosure-type of soundproofing MAM. In addition, the vibration displacement of the MAM enclosure exterior wall is measured using laser Doppler vibrometer. The results show that the soundproofing MAM exhibits excellent sound-blocking characteristics at multiple anti-resonance frequencies compared to homogeneous materials of the same weight. We expect that its simple construction can be used in noise-insulation applications in acoustic enclosures, automobile insulation, walls, and engine rooms.