Molded metamaterial plate for reduction of sound transmission through automotive door

This study presents a low-cost, mass-producible acoustic metamaterial designed to reduce road noise in vehicles by improving sound transmission loss in door trims. Unlike previous designs relying on complex structures unsuitable for mass production, the proposed solution uses a single-material, single-process molding method. The metamaterial consists of a periodic array of protrusions on a silicone plate and is designed via dispersion analysis to create a band gap in the sub-1000 Hz range that is critical for suppressing road noise. Experimental measurements demonstrate that these molded plates improve sound transmission loss by approximately 2 dB in the band-gap frequencies compared with flat plates of equivalent mass. When installed in the door trims, the metamaterial improves frequency response functions, resulting in a reduction of interior noise by approximately 1.4 dB at 40 km/h. Overall, this study demonstrates that this simple, integrable metamaterial structure can effectively improve the sound transmission loss without added mass or production complexity, making it viable for automotive mass production and other large-scale industrial applications.