Imaging the spatial variation of dielectric constant in materials using microwave near field microscopy

This work presents an investigation of high spatial resolution subwavelength imaging of conductivity variations in materials using microwaves. The purpose of this investigation is to gain a better understanding of the imaging capabilities and contrast mechanisms that affect microwave near field microscope measurements. Previous work has attempted to separate changes in reflected microwave power resulting from topography versus material property changes. The efforts in this study investigate how topography influences reflected microwave power measured in the near field, how material property changes (specifically changes in a material's dielectric constant) influence reflected microwave power in the near field, and to determine if these effects can be separated for high resolution imaging. Maxwell's equations were solved for electromagnetic fields at an observation point generated from a dipole above a half space without limiting the solution to the far field. By avoiding the restrictions on the observation distance, electromagnetic field solutions were derived for the near field. The magnitude of the total electric field was calculated at an observation point for dipoles above a half space with varying conductivities to study how material property changes affect the magnitude of the total electric field and the contributing fields. The magnitude of the electric field was calculated for varying dipole distances above a metal half space and a semiconduting half space to study how topography affects the magnitude of the electric field. A microwave near field microscope was constructed to measure approach curves and create images of various samples for study. It was determined that all the contributing fields, direct, image, and surface wave terms, are affected by topography changes but only the surface wave terms are affected by changes in the material property of the half space.