THERMAL NONDESTRUCTIVE EVALUATION USING MICROWAVE SOURCES

The development of thermographic nondestructive evaluation techniques using microwave heating methods is described in this paper Microwave h eating provides unique capabilities ies for selective heating of defec ts and for the deposition of heat at depth in the specimen. This can i mprove the spatial resolution, sensitivity, and speed of the thermal i nspection process relative to conventional thermographic techniques wi th optical heating. Analysis of tire expected time-development of the surface temperature is presented for a series of specimen geometries a nd supporting experimental results are given. Systems studied include a test specimen with water at a series of different depths, a disbonde d coating with water at the interface, a composite specimen with embed ded carbon fibers, and a composite specimen which had experienced impa ct damage. The dependence of the thermographic response on the polariz ation and angle of incidence of the microwaves is examined. Quantitati ve information about the depth of defects and about the thermal proper ties of the specimens is obtained from analysis of the time-dependence and spatial-dependence of the temperature distribution during microwa ve heating. The results presented here provide the groundwork for the development of embedded sensors for process control which can be remot ely activated by microwaves and remotely interrogated by infrared radi ometry methods.