A practical acoustic metamaterial sheet available for ultra-lightweight sound insulators

What is it about?

There has been a strong demand for lightweight sound insulators because of increasing needs for weight reduction of vehicles for higher energy efficiency and recent tightening of the noise regulation in many countries. However, commonly used sound insulators composed of iron or rubber materials require heavy weights to realize high sound insulation according to the mass law. Therefore, advanced acoustic metamaterials that comprise periodically arranged resonance structures and break the mass law limit at a certain frequency have attracted great attention from both academia and industry. However, their feasible industrial applications are still extremely limited mainly because of the time-consuming and multi-step processes in the production and assembly. 　In this paper, we designed a cylindrical silicone rubber stub with an embedded metallic weight as a spring-mass local resonator and connected the discrete resonators two-dimensionally through an integral molding method by taking advantage of our material processing techniques to develop a practical acoustic metamaterial sheet. The integration design into a sheet-like material enables the mass production of the acoustic metamaterial and single-step assembly of numerous resonators on a target object with high positioning accuracy, where the sheet works as a ultra-lightweight sound insulator to prevent invasion of airborne sound and/or radiation of acoustic noise emanated from the objects. Specifically, to achieve sound insulation of 40 dB at 800 Hz, a normal iron plate needs an area density of 60 kg/m2, whereas our acoustic metamaterial sheet just weighs 7.8 kg/m2 to achieve the same performance, which means that one can reduce the weight of sound insulation materials by 87%. The target sound insulation frequencies can be adjusted in a broad frequency range by tuning the physical properties, dimensions and weights of the resonators. 　We are currently exploring its appealing applications for automobiles, railways, airplanes, construction machines and home electronics having motors, fans and vibrating components, which emit undesirable acoustic noise at particular frequencies. Please do let us know if you want any further information on our acoustic metamaterial sheet.

Featured Image

Photo by Mitchell Luo on Unsplash

Photo by Mitchell Luo on Unsplash