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Acoustic metamaterials with combined heterogeneous double-split hollow sphere for noise reduction

We present the concept design of a new class of acoustic metamaterial structure based on a combined heterogeneous double-split hollow sphere (CHDSHS). These structures are local resonators possessing subwavelength band gaps. The present CHDSHS metamaterial structures are made of plastic sphere structures with two different holes. The main novelty of a CHDSHS relies in the significant noise reduction obtained and the simplicity of manufacture. Their characteristics in band gaps are influenced by the volume sizes of the plastic sphere and the areas of the two holes. The CHDSHS metamaterials are combined to increase pressure attenuation over a wide frequency range. The frequency shifts in the band gap due to the changes in size are formulated and discussed in detail. Furthermore, the band gaps of the present CHDSHS metamaterials are numerically and experimentally demonstrated.