Ultra-broadband and nonlinear robust sound absorption based on ultra-microperforated panel

An ultra-broadband sound absorber with excellent nonlinear robustness is proposed. The absorber consists of an ultra-microperforated panel (UMPP) with the orifice diameter of less than 0.1 mm and three back cavities. The UMPP has a stable impedance matching the air characteristics impedance, thus being selected as the acoustic resistance component. Three back cavities with a height-doubling recursive relationship are designed as the acoustic reactance component, which greatly expands the near-zero acoustic reactance frequency bandwidth. After space optimization, the proposed 71-mm high UMPP sound absorber achieves a mean absorption coefficient α of 0.965 in the quasi-perfect band ranging from 540–3800 Hz. Moreover, the UMPP absorber shows excellent robust sound absorption at extremely high sound intensities. Experimental results suggest the absorption coefficient is still greater than 0.8 in the range of 600–4000 Hz with a 155 dB sound pressure level. Based on the theoretical analysis, small orifice diameter, large percent open area, and large aspect ratio are the key geometric features for achieving good nonlinear robustness. The proposed UMPP absorber has potential in aerospace noise-control engineering owing to its ultra-broadband absorption performance, simple structure, excellent nonlinear robustness, and good aerodynamic performance.