Thermal imaging of subsurface microwave absorbers in dielectric materials

The use of microwaves as a heating source in time-resolved IR radiometry provides the ability to heat surface and subsurface microwave-absorbing regions of a specimen directly. This can improve the contrast and spatial resolution of such regions and enhance their detectibility when compared with conventional laser or flashlamp sources. The experiments reported here use microwave heating with IR detection. Results on plexiglass-water-Teflon test specimens with absorbers at different depths in the sample are described by a 1D analytical model. Measurements using microwave and optical heating on epoxy-coated steel pipes are compared and demonstrate the ability of microwave heating to detect subsurface water voids very efficiently. Other applications of the method to microwave imaging, field mapping and imaging of defects in composite materials are discussed.