  By considering the membrane's dissipation, the membrane-type acoustic
metamaterial (MAM) has been demonstrated as a super absorber for low-frequency
sound. In the paper, a theoretical vibroacoustic plate model is developed to
reveal sound energy absorption mechanism within the MAM under a plane normal
incidence. Based on the plate model in conjunction with the point matching
method, the in-plane strain energy of the membrane due to the resonant and
antiresonant motion of the attached masses can be accurately captured by
solving the coupled vibroacoustic integrodifferential equation. Therefore, the
sound absorption of the MAM is obtained and discussed, which is also in good
agreement with the prediction from the finite element method. In particular,
microstructure effects including eccentricity of the attached masses, the
depth, thickness and loss factor of the membrane on sound absorption peak
values are quantitatively investigated.
