Research on Hybrid Absorption Based on Acoustic Impedance

In this paper, a new hybrid absorption system is posed which is composed of a layer absorbent material and a movable rigid wall. The speed of the movable rigid wall is adjusted in order to make the acoustic impedance of the absorption material match the acoustic impedance of the air, so that the absorption coefficient is maximal. Finally, a numerical calculation and an experiment are carried out, both numerical and experimental results of such a system are presented for a normally incident plane wave. The numerical and experimental results indicate that the absorption effect is effecting at middle and low frequencies and imperfect in high frequencies where passive absorption is dominant.