Sound absorption characteristics of underwater flexible micro-perforated sound absorption structures

A mathematical model for the micro-perforated panel in water medium is established using mode superposition method,and an equivalent circuit model is acquired based on electro-acoustic analogy method.Effects of the flexible micro-perforated panel(FMPP) and the flexible back panel(FBP) on normal incidence sound absorption coefficient are analyzed.Unlike micro-perforated panel in air medium,the underwater micro-perforated panel cannot achieve any satisfactory sound absorption effect due to insufficient structural impedance.To this end,a strengthened micro-perforated sound absorption structure is proposed.Theoretical results are verified in a water-filled impedance tube.Within the range from 20 Hz to 2,000 Hz the average absorption coefficient of the strengthened flexible micro-perforated panel are improved obviously.The absorption coefficient curve gradually approaches rigid micro-perforated panel as the bending stiffness increases.The flexible back panel can reduce the resonance frequency of the absorption curve and improve the low-frequency sound absorption performance.