Numerical filters as a tool for defect characterization in pulsed thermography

Abstract
A calibration approach using numerical filters to characterize defects detected by pulsed thermography in polymers with different optical transparency was developed and tested. Calibration was realised by simulation of the measurement. Seventeen measurement quantities were taken from the simulation results, that supplied the numerical filter coefficients via a multi-dimensional linear regression. Measurements using flash excited thermography on black polyoxymethylene specimens with flat bottom holes resulted in very good defect depth and width reconstruction, whereas for more transparent polyamide specimens the reconstruction was less accurate.