Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Origin of Negative Density and Modulus in Acoustic Metamaterials   This paper provides a review and fundamental physical interpretation for the
effective densities and moduli of acoustic metamaterials. We introduce the
terminology of hidden force and hidden source of volume: the effective density
or modulus is negative when the hidden force or source of volume is larger
than, and operates in antiphase to, respectively, the force or volume change
that would be obtained in their absence. We demonstrate this ansatz for some
established acoustic metamaterials with elements based on membranes, Helmholtz
resonators, springs and masses. The hidden force for membrane-based acoustic
metamaterials, for instance, is the force from the membrane tension. The hidden
source for a Helmholtz-resonator-based metamaterial is the extra air volume
injected from the resonator cavity. We also explain the analogous concepts for
pure mass-and-spring systems, in which case hidden forces can arise from masses
and springs fixed inside other masses, whereas 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. This overall picture provides a powerful tool for
conceptual understanding and design of new acoustic metamaterials, and avoids
common pitfalls involved in determining the effective parameters of such
materials.

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The categories of this paper are: bayes-an
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The categories of this paper are: q-bio
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The categories of this paper are: astro-ph
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The categories of this paper are: funct-an
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The categories of this paper are: comp-gas
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The categories of this paper are: hep-ph
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The categories of this paper are: patt-sol
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The categories of this paper are: cond-mat
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The categories of this paper are: hep-lat
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The categories of this paper are: chao-dyn
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The categories of this paper are: eess
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The categories of this paper are: dg-ga
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The categories of this paper are: plasm-ph
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The categories of this paper are: nucl-ex
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The categories of this paper are: nucl-th
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The categories of this paper are: chem-ph