A Hybrid Microwave NDE System for Rapid Inspection of GFRP Composites

The last few decades have seen a significant increase in the use of composite materials in the aerospace, automotive, and civil industries, largely due to the advantages they offer in terms of low weight, corrosion resistance, and excellent thermo-mechanical properties. Appropriate nondestructive evaluation (NDE) techniques that allow for rapid detection of damage and assessment of its severity in composites still remains an area of active research. There is a need for a reliable NDE system that can be used to rapidly inspect these structures and prevent catastrophic failure. High-frequency electromagnetic NDE techniques are well suited for low-loss dielectric materials because of the ability of the electromagnetic waves to interact with these materials. Glass fiber-reinforced polymers (GFRP) are inherently dielectric, thus facilitating the use of microwaves for their inspection. While far-field electromagnetic inspection systems have the capability of rapid, large-area inspection because of its large stand-off measurement capability, near-field techniques enable higher resolution and exact sizing of discontinuities. This paper presents ongoing work on the development of a novel, hybrid electromagnetic imaging system (HEMIS) for NDE of GFRP structures that combines benefits of both near-field and far-field inspection systems. The experimental systems and imaging algorithms characterizing the far-field and near-field systems are developed and discussed. Experimental imaging results for detecting practical, challenging damage modes in GFRP composites and metal composite joints demonstrate the efficiency of the system with novel capabilities, such as rapid, large-area inspection and subsurface high-resolution imaging. The fusion of the results from the two techniques provides a robust approach for NDE of composite materials.