PRELIMINARY-STUDY OF THE INFLUENCES OF EFFECTIVE DIELECTRIC-CONSTANT AND NONUNIFORM PROBE APERTURE FIELD DISTRIBUTION ON NEAR-FIELD MICROWAVE IMAGES

Near field microwave imaging is based on transmitting a wave into a di electric structure, which is located in the near field of a sensor and using a signal proportional to the magnitude and/or phase of the tran smitted or reflected wave to create a two or three dimensional image o f the structure under investigation. To analyze the features and prope rties of an image, it is important to understand the mechanism by whic h the incident electric and magnetic fields interact with the structur e. In this study, an effective dielectric constant formula is used to model the reflection properties of two and three dielectric half space s arranged side by side when scanned by an open ended rectangular wave guide probe. Importantly, the influence of the nonuniformity associate d with the electric field distribution at the waveguide aperture is in vestigated as well. To this end, linear and nonlinear volume fraction calculations are incorporated to calculate the effective dielectric co nstant of the specimens made of two and three dielectric half spaces. Consequently, the phase and magnitude of the reflection coefficient at the waveguide aperture are calculated. Theoretical and experimental r esults are presented and compared. In addition, a discussion related t o the relative influences of the effective dielectric constant and ape rture field distribution is presented.