Sizing horizontal metallic inclusions in insulators using lock-in inductive infrared thermography

We present a methodology to size the area and depth of horizontal metallic inclusions of unknown geometry, embedded in insulators, using lock-in inductive thermography. The method is based on averaging the amplitude and phase thermograms along circles concentric with the center of the heated region. We present an analytical calculation of the surface temperature distribution produced by a horizontal circular heat source, taking into account conductive coupling with the air, and we propose to fit the averaged data to this model. We present lockin thermography data on resin samples containing embedded calibrated circular and rectangular Cu slabs that we excite inductively. The results indicate that it is possible to determine the area and depth of rectangular heat sources with aspect ratio below 1.5 with accuracy better than 10 %.