Imaging of Near-Surface Defects using Microwaves and Ultrasonic Phased Array Techniques

Detecting and imaging near-surface defects is of significant importance in many applications. Detecting corrosion/defects under thin paint layer applied on metallic substrates, evaluating debond under a Teflon coat, as well as evaluating the integrity of the dielectric coats remains a challenge in many industries settings. Periodic testing is imperative for a wide range of industries to isolate material defects that could lead to catastrophic failures, expensive repairs, or a complete shutdown. Out of the many non-destructive testing (NDT) techniques available, phased array ultrasonic testing (PAUT) is widely used in various industries for material inspection. It has shown exceptional capability in detection of defects, including material loss and corrosion in metals. On the other hand, near-field microwave NDT is emerging as a powerful inspection modality for similar applications. In this paper, imaging capabilities of PAUT (5 MHz) as well as near-field microwave imaging system (33.5 GHz) are discussed and evaluated for a number of specimens with man-made surface defects. The evaluated defects include flat bottom slots, holes and corrosion-under-paint. Images produced by both techniques are presented. The images produced by the microwave imaging system are benchmarked with PAUT system.