The acoustic performances of a subwavelength hierarchical honeycomb structure: Analytical, numerical, and experimental investigations

This paper proposes a subwavelength hierarchical honeycomb structure (SHHS) with a compact lateral dimension and double-band perfect absorption in low frequencies. Unlike the conventional micro-perforated panel (MPP)-honeycomb sandwich absorber, this structure has an additional internal honeycomb with a perforated wall. Therefore, there are two resonant cavities in the SHHS to realize multiple absorption peaks. Analytical, numerical, and experimental investigations are performed to study the proposed system's acoustic performance in absorption. The SSHS is simplified into four parts and its analytical model is constructed by combining various analytical models by acoustic-electro analogy. The analytical model is presented to explore the physical properties of sound absorption and the influence of parameters, which has been validated by comparisons with the numerical model, and the experimental data is measured by an impedance tube. It is found that the main incident energy is lost by the inside hole, which is different from the conventional absorbers with surface MPP. Moreover, the side length of the internal honeycomb can adjust the resonant frequencies to achieve an absorber with the subwavelength. A SSHS is designed with a perfect absorption at 320 Hz whose thickness is 1/31 of the resonant frequency wavelength. The SHHS has excellent potential for noise control engineering applications.