Self-consistent photoacoustic techniques for thermal diffusivity measurements of self-curable resins

Two self-consistent photoacoustic methodologies, for measuring thermal diffusivity of self-curable resins, are presented. These methodologies make use of the analytical solution for the one-dimensional heat diffusion problem for a three-layer system, assuming the surface absorption model. The analytical procedure relies on the normalization of the theoretical photoacoustic signal from the three layers with the corresponding signal from the uppermost two layers, involving linear fits on the normalized amplitude (in semilog scale) and phase, as functions of the modulation frequency root square. The normalization procedure eliminates the frequency-dependent instrumental electronic contribution (transfer function) and some thermophysically nonrelevant proportionality factors in the theoretical equations, thus making the analysis feasible. The thermal diffusivity of two different self-curable resins was measured and good agreement was obtained between results from both the amplitude and phase, showing consistency between these two photoacoustic methodologies.