Origin of negative modulus

We present a new view point for effective moduli of acoustic metamaterials. We introduce the concept of hidden source of volume: the effective modulus is negative when the volume of fluid injected from the hidden source is larger than, and operates in antiphase to, the volume change of the unit cell...

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Bibliographic Details
Published in:The Journal of the Acoustical Society of America 2016-04, Vol.139 (4), p.2182-2182
Main Authors: Lee, Sam Hyeon, Wright, Oliver B.
Format: Article
Language:English
Online Access:Get full text
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Summary:We present a new view point for effective moduli of acoustic metamaterials. We introduce the concept of hidden source of volume: the effective modulus is negative when the volume of fluid injected from the hidden source is larger than, and operates in antiphase to, the volume change of the unit cell that would be obtained in its absence. We demonstrate this ansatz for some established acoustic metamaterials with elements based on Helmholtz resonators and side holes. The hidden source for a Helmholtz-resonator-based metamaterial is the extra air volume injected from the resonator cavity. The hidden sources—more aptly termed hidden expanders of displacement in this case—can arise from light rigid trusses coupled to extra degrees of freedom for mechanical motion such as the case of coupling to masses that move at right angles to the wave-propagation direction.
ISSN:0001-4966
1520-8524
DOI:10.1121/1.4950487