Negative mass sound shielding structures: Early results

Elastic meta-materials or meta-composites can be designed to have a negative effective mass density at certain vibration frequencies, thus blocking wave propagation through the material within that frequency band. The negative mass behaviour is generated by resonant structures within the material that oscillate 180 degrees out of phase with the acoustic pressure waves applied to the surface. As this research is in its initial stages this paper describes work in progress in both the experimental and numerical domains, and some early results from solids containing geometrically, simple spring-mass resonant structures. Behaviour is characterized experimentally by dynamic tests of individual resonators as well as impedance tube measurements of panel-like structures containing multiple resonant elements. The experimental results exhibit clear evidence of the expected resonances, and partial band gap behaviour. Finite element models of both single resonant elements and impedance tube specimens are being developed, and the current status of these models is described. Their results to date show good agreement with the mass law and qualitative agreement with the experimental results.(C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim