On the applicability of the effective medium approximation to the photoacoustic response of multilayered structures

If the model of the photoacoustic (PA) response of an investigated system contains many unknown parameters, as is the case with multilayered samples, then the inverse procedure for the calculation of the parameters is highly sensitive to experimental noise. The problem cannot be solved by developing the experimental setup or by data acquisition methods, but only by an improvement of the theoretical approach. This paper presents an analysis of the applicability of the effective medium approximation to the PA response of multilayered samples. It has been shown that the theory is not applicable to the general case, and explicit expressions for the effective values of thermal diffusivity and heat propagation speed have been derived for some special cases.