Nondestructive assessment of microwave absorbing structures via active microwave thermography

Abstract

Radio-frequency absorbing materials (RAM) are widely used to reduce electromagnetic interference and scattering from reflective (e.g. conductive) surfaces such as those utilized in aerospace and military applications. Thus, it is important to nondestructively assess such structures for their structural health (i.e., defect detection). To this end, active microwave thermography (AMT) is considered as a viable solution. AMT utilizes a microwave-based thermal excitation for structures/materials under inspection. The resulting surface thermal profile is measured with a thermal camera. As it relates to structures with a microwave-absorbing surface, the surface (when illuminated by microwave radiation) absorbs this energy and thus acts as a thermographic heat source. In order to show the practical applicability of AMT for inspections of the aforementioned structures, two carbon-fiber reinforced polymer (CFRP) samples (containing defects), with and without RAM, are inspected. The results show that the detection capability is significantly improved when the samples contain RAM on their surface, thereby illustrating the efficacy of AMT for inspection of such structures.