Hybrid composite meta-porous structure for improving and broadening sound absorption

In order to improve and broaden the sound absorption performance of porous materials with low flow resistance, this study proposes the composite meta-porous structure embedded multiple lateral plates of different lengths, and investigates the corresponding sound absorption coefficients with the fixed and periodic boundary. Characteristics of spatial fluctuation and slow wave effect are embodied in acoustic pressure distributions. Further, the hybrid composite meta-porous structure with periodic boundary could achieve high sound absorption in range of 0–6.4 kHz. The Theoretical model using transfer matrix method suitable for these models is proposed, and verify the FEM results. Normalized surface impedance, phase and trajectory of the complex reflective coefficient illustrates the loss of acoustic energy inside the structure and leakage to the outside. By detailed discussion on the relationship between the geometric parameters and the corresponding sound absorption coefficients, the three boundaries would have different effects on sound absorption performance. Sound absorption test results by acoustic impedance tube confirm the rationality of the composite meta-porous structure with fixed boundary in range of 0.2–5.716 kHz and its practical application in the noise reduction.