Resonant modal group theory of membrane-type acoustical metamaterials for low-frequency sound attenuation

¹ School of Mechanical Engineering and State Key Laboratory for Strength and Vibration of Mechanical Structure, Xi’an Jiaotong University, 71009 Xi’an, P.R. China
² State Key Laboratory of Explosion Science and Technology, Beijing Institute of Technology, 100081 Beijing, P.R. China

^a e-mail: ejhwu@mail.xjtu.edu.cn

Received: 18 June 2015
Revised: 24 July 2015
Accepted: 27 July 2015
Published online: 27 August 2015

Abstract

In order to overcome the influence of the structural resonance on the continuous structures and obtain a lightweight thin-layer structure which can effectively isolate the low-frequency noises, an elastic membrane structure was proposed. In the low-frequency range below 500 Hz, the sound transmission loss (STL) of this membrane type structure is greatly higher than that of the current sound insulation material EVA (ethylene-vinyl acetate copo) of vehicle, so it is possible to replace the EVA by the membrane-type metamaterial structure in practice engineering. Based on the band structure, modal shapes, as well as the sound transmission simulation, the sound insulation mechanism of the designed membrane-type acoustic metamaterials was analyzed from a new perspective, which had been validated experimentally. It is suggested that in the frequency range above 200 Hz for this membrane-mass type structure, the sound insulation effect was principally not due to the low-level locally resonant mode of the mass block, but the continuous vertical resonant modes of the localized membrane. So based on such a physical property, a resonant modal group theory is initially proposed in this paper. In addition, the sound insulation mechanism of the membrane-type structure and thin plate structure were combined by the membrane/plate resonant theory.