Investigation of Helmholtz resonator-based composite acoustic metamaterial
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The emergence of composite metamaterials broadens the concept of exotic properties that are not found in nature. In this paper, a composite metamaterial composed of Helmholtz resonators and periodic arrangement of plate is investigated analytically and numerically and a new property of the structure is explored. The structure becomes transparent at the vicinity of plate cutoff frequency even though Helmholtz resonator attained a positive bulk modulus, which is not achieved using side hole metamaterial composite. The resonance absorption of Helmholtz resonator makes Helmholtz-based composites not to be used for applications that need higher transmission even though negative bulk modulus is achieved. In this paper, we also show that Helmholtz resonator-based composite metamaterials can be used as impedance matching layers. The Helmholtz resonator-based composite structure became transparent at the band gap region of Helmholtz resonator, where both components are below cutoff frequency. Further, based on cloaking concept we demonstrated its application to enhance transmission through skull layer. The transmission can be controlled by manipulating plate thickness and Helmholtz resonator dimension.
This research was supported by the Basic Science Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2016R1D1A1B01016264).