Broadband sound absorption under oblique incidence based on ultra-micro-perforated panel absorber

This study systematically investigates the acoustic characteristics of an ultra-micro-perforated panel (UMPP) absorber under oblique incidence through theoretical analysis and numerical simulations. The proposed absorber consists of a MPP with sub-100 μ m apertures and three back cavities with approximately recursive height relationships. Finite element simulations reveal that the sound absorption coefficients exhibit slight variation within polar incident angles of 0∘–45∘, reaching optimal performance at 45∘, followed by progressive decrease with increasing angles beyond this threshold. Impedance matching analysis demonstrates that at 45∘ incidence, the equivalent acoustic impedance of UMPP optimally matches the air characteristic impedance, while smaller and larger incident angles manifest overdamped and underdamped characteristics respectively. The azimuthal angle shows negligible influence on absorption performance, attributed to preserved system coupling characteristics. Discrete integral calculations for diffuse field conditions indicate that the UMPP absorber achieves an average absorption coefficient of 0.9 across 540–3800 Hz frequency range, demonstrating superior broadband sound absorption performance.