| CPC G10K 11/162 (2013.01) [G10K 11/161 (2013.01)] | 17 Claims |

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1. An acoustic metamaterial structure comprising:
multiple first unit cells each comprising a first space having a first cross-sectional area and a second space disposed downstream of the first space in a flow direction of fluid to communicate with the first space, the second space having a second cross-sectional area larger than the first cross-sectional area,
wherein at least one of the multiple first unit cells communicates with a flow pipe through which the fluid flows,
the multiple first unit cells are sequentially arranged in a longitudinal direction of the flow pipe, and
the acoustic metamaterial structure reduces noise in a specific frequency range through formation of an acoustic bandgap, the specific frequency range being determined by a periodic structure formed by an array of the first space and the second space; and
a neck extension member extending from the first space to protrude inwardly of the second space,
wherein the first space has a shape bent at a 90-degree angle, with one end connected to the flow pipe and the other end connected to the second space.
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