The comparative analyses of the calculation methods for absorptivity of multilayer micro-perforated panel absorbers

The absorptivity of multilayer micro-perforated panel absorber(MPA) usually is estimated by the equivalent circuit(EC).Recently,there are attempts to use the impedance transfer method(ITM) or the transfer matrix method(TMM) to calculate the absorptivity.It is necessary to compare the three methods.The corresponding experiments are carried out for the comparison.Theoretical analysis and experimental results show that the ITM and TMM are the essentially same,and their calculation results are consistent with the experimental data.However,the calculations results using EC disagree with experimental data,especially for the structure with long cavity.EC is a kind of concentrated parameter analysis method.For a multilayer structure,this method only considers acoustic compliance,while ignores the effect of acoustic mass.Thus,it will cause calculation error.This kind of error does not exist in ITM and TMM,thus they are more accurate than EC.