Design of a resonant metamaterial based acoustic enclosure

Periodic structures, such as honeycomb core panels, combine excellent mechanical properties with a low mass, making them attractive for application in transport and machine design. However, the high stiffness to mass ratio of these lightweight panels may result in unsatisfactory dynamic behaviour in that it may impair the panels' ability to reduce noise and vibration levels. Liu et al. demonstrated that inclusions of high density spheres with a rubber coating in a matrix material result in low frequency sound isolation breaking the mass law [7]. These locally resonant metamaterials require a high density of local resonators throughout the matrix material, either spread randomly or periodically. In a previous paper by the authors, resonant structures were introduced into the cavities of a honeycomb structure with large cells (30 mm width), leading to a material with strong vibrational attenuation in a low frequency region [3]. In the present paper the potential for acoustic stop bands is shown through a demonstration on an industrial relevant test case: a periodic structure of cells with 10mm width and added local resonant structures. The existence of acoustic stopbands is experimentally proven, clearly showing that stopbands can improve the acoustic behaviour of lightweight panels.