High-resolution millimeter-wave imaging system for defect characterization in dielectric slabs

Preliminary results are presented for a millimeter-wavelength free-space imaging system used to detect and characterize defects in layered dielectric composite slabs. Such systems throughout the microwave spectrum have shown great potential as alternative nondestructive evaluation tools for on-line, in-situ examination of low-loss dielectric materials such as plastics, ceramics, and various dielectric composites. Results of a fixed-frequency W-band imaging system operating in either through-transmission or reflection mode are presented here. Incorporation of focused-beam antennas allows high-resolution measurement of small variations within the sample under test. The results are based on measurement of the relative amplitude and phase of the reflected or transmitted wave in monostatic or bistatic configurations, respectively. With proper calibration, the measured parameters can be used to estimate dielectric property variations within the material media. A theoretical simulation for plane wave propagation in a multilayered media is used to interpret the measurement results.