A lightweight and transparent acoustic metamaterial sheet with designed structures for sound insulation applications

Normal sound insulation materials such as metal plates and rubber sheets follow the mass law. According to the mass law, a weight increase of sound insulators leads to high sound insulation. Therefore, novel lightweight and high-performance materials have been required in various fields such as mobility and electronics. We developed lightweight and transparent acoustic metamaterial sheets having blocklike weights with rodlike or cylindrical shapes periodically arranged on thin films. Upon sound incidence at a target frequency, the heavier weights and the lighter film cooperatively vibrate in opposite phase and with the same amplitude. The transmitted sound waves through those parts cancel each other out owing to the wave interference. As a result, the acoustic metamaterial sheets show high sound insulation performance beyond the mass law limit at the target frequencies. In this study, we report the structural design, sound insulation properties and mechanisms, and application of acoustic metamaterial sheets.