Photothermal tomography for the functional and structural evaluation, and early mineral loss monitoring in bones
InfraRed Thermography (IRT) is a promising approach for Non-destructive Testing and Evaluation (NDT&E) of various materials due to its inherent merits such as remote, whole-field, qualitative and quantitative inspection capabilities. Of various thermal NDT&E techniques, nonstationary thermal wave imaging methods have gained a wide acceptance due to their fast inspection capabilities by using moderate peak power heat sources over the conventional widely used active thermographic methods such as pulse (pulse and pulse phase) based and sinusoidal modulated (lock-in) thermographic techniques. This work highlights various non-stationary modulated thermal wave imaging (TWI) techniques such as frequency modulated thermal wave imaging (FMTWI) and its digitized version of FMTWI (DFMTWI). In this paper, a finite element based analysis has been proposed to model a mild steel sample containing flat bottom holes as subsurface defects located at different depths. Further, widely used post processing techniques (based on time and frequency domain) have been applied and the comparisons have been made among them for sub-surface defect detection.