Frequency Modulated Thermography-NDT of Polymer Composites by Means of Human-Controlled Heat Modulation

The present work proposes a frequency modulated Infrared NDT low-cost setup. In particular, heat modulation is human-controlled by acting on a simple switch used to trigger common halogen lamps. The acquired thermal sequence is processed by Matlab scripts based on Least Square Fitting (LSF) and Discrete Fourier Transform (LSF). LSF is in particular performed using an harmonic analytical model, where a nonlinear fitting procedure, based on a pattern-search algorithm, allows to optimise the harmonics frequencies. The proposed processing schemes are implemented on experimental data acquired from a Glass Fibre Reinforced plate with artificial back-hole and embedded patch defects. The two LSF and DFT approaches are compared investigating phase maps at different frequency bins.