NDE for Metals, Composites and Semiconductors by Frequency Modulated Thermography

Active thermography is a relatively new NDE technique, in which either a pulse or sinusoidal thermal stimulus forms the basis for conventional Pulsed (PT) and Pulsed Phase (PPT), and Lock-in (LT) Thermography respectively. Recently a new approach to active thermography was proposed in which the thermal stimulus is frequency modulated. In Frequency Modulated Thermal Wave Imaging (FMTWI), a specimen is heated for launching thermal waves into the sample, not at a single frequency (lock-in) or at all frequencies (pulsed), but in a desired range of frequencies in a decided time span. While peak power requirement is reduced, phase images obtained retain known advantages of reduced sensitivity to surface conditions, variations in emissivity and non-uniform heating. The techniques applicability to a variety of materials is highlighted by providing experimental results for metal, semiconductor and composite samples.