Because of the proximity of the porous material, the oscillating air molecules inside the absorber lose their acoustical energy due to friction.
The main reason why Micro Perforates have become so popular among acousticians is that they have a good absorption performance but without the disadvantages of a porous material.
By varying geometrical and material parameters, the acoustical performance can be tailored to meet a multitude of specifications in various applications.
One early contributor to the theory of micro perforated plates as sound absorbers was Professor Daa-You Maa.
One other major phenomenon that currently being investigated is the nonlinear effect i.e. an MPP behaves differently depending on the magnitude of the incident sound wave.