Detection/Location of Small Flaws in Composite Structures Using Microwaves

The use of high-frequency electromagnetic radiation (“microwaves”) in a variety of NDE scenarios has been receiving increased attention recently [1], largely as the result of advances in microwave instrumentation, computer technology and digital signal processing. Microwave images of both surface and interior features of non-conducting samples can be generated either by focusing the energy on the smallest possible spot and scanning either the target or the measurement probe (analogous to an ultrasonic C-scan), or by using coherent processing to form an image from multiple exposures of the entire target [2,3]. The latter approach, as implemented in an “Inverse-Synthetic-Aperture Radar” (ISAR) system has the significant advantage of being able to image complex, large and oddly shaped targets from a large stand-off distance (many meters). The results presented below give an indication of the great sensitivity of the IS AR technique in its ability to detect and locate very small flaws in a complex target.