Study of the effect of shape on acoustic performance of micro perforated absorbent at low frequencies

Introduction: Micro-perforated absorbents are one of the structures that are widely used nowadays. The sound absorption mechanism is performed by viscous energy losses in the cavities on the plate. In this study, the acoustic properties of non-flat perforated panels in oblique angle was investigated in numerical method. Material and Methods: This paper examined the effect of the surface shape on the micro perforated absorber performance at low frequencies (less than 500 Hz). The three-dimensional finite element method was used to predict the absorption coefficient of this group of adsorbents. Also, the results obtained from the shaped absorbents were compared with the flat micro perforated ones. After validating the numerical results, six different designs were defined as the surface shape of the micro perforated plates in the COMSOL Multiphasic, Ver. 5.3a software Results:  The results reflected the fact that the factor of the surface shape can be used as a contributing factor in lower frequencies. In general, the dented or concave shapes provide better outcomes than other flat designs and shapes and the convex or outward shapes bring the weakest results. Conclusion: To explain this function, shaping creates a phase difference and angling the sound wave and creates a variable depth behind the micro-perforated plate. It also influences the reflection process which affect the absorption coefficient.