Surface defects mapping using microwaves and ultrasonic phased array imaging

Ultrasonic testing (UT) techniques are extensively used for nondestructive testing (NDT) of material structures in various industries. In particular, phased array UT systems have proven significant industrial utility for a wide range of inspection applications including corrosion and material loss mapping in metals. On the other hand, near-field microwave NDT is emerging as powerful inspection modality for similar applications. Consequently, it becomes imperative to benchmark the capabilities of these modalities on common test specimen. In this paper, a practical evaluation of the capabilities of these two techniques for surface defect imaging is presented and discussed. A near-field microwave imaging system operating at 24 GHz as well as a 5 MHz phased array UT system are introduced and described. A varying set of test specimen which includes surface defects such as flat bottom holes, slots, and corrosion-under-paint are imaged using both modalities. The resulting C-scan images of the two systems are reported and compared. It is shown that, even when the utilized microwave frequency is relatively low, the microwave system produces images with comparable resolution to those produced with the UT phased array system.