In Pulse Compression Thermography, the impulse response of the sample under test is retrieved pixelwise by applying a proper matched filter on the set of acquired thermal images. Linear frequency-modulated chirp signals and binary codes are the most employed coded excitation exploited in Pulse Compression Thermography. To improve the detection capability of the technique, a non-linear frequency modulated chirp signal can be used to deliver more energy to sample in a wanted frequency range of interest. In this work, we report the application of an exponential chirp to modulate the heating source and we compare it with a standard linear chirp excitation. To do a fair comparison, various windowing functions have been applied on the matched filters to reduce range sidelobes, thus enhancing the retrieved impulse response quality. It is shown that the combined use of an exponential chirp and an appropriate matched filter obtain exploiting the Reactance Transform provides a faithful reconstruction of the sample impulse response and an enhanced signal-to-noise ratio with respect to the use of linear chirp. This has been demonstrated on a 3D-printed PMMA sample containing sixteen flat-bottom holes of different depths.

Available online at: https://www.qirt2018.de/portals/qirt18/doc/We.3.B.4.pdf