"Microwave imaging techniques are well suited for NDE of dielectric materials such as composites because of the ability of microwaves to propagate through and interact with these materials. The scattered field provides information about the discontinuity in dielectric properties and hence structural integrity of these materials. While far field electromagnetic inspection systems have the capability of rapid, large area inspection because of large standoff measurement capability, near field techniques enable higher resolution and imaging of anomalies. Moreover, the wide range of the electromagnetic spectrum allows greater penetration using lower frequencies and better resolution at higher frequencies. A synergistic integration of far field and near field techniques into a hybrid monitoring system is therefore promising. This research aims at developing a novel, hybrid electromagnetic imaging system (HEMIS) that combines benefits of both near field and far field electromagnetic systems. The development of a new system that will utilize novel antenna design and sensors, coupled with time reversal imaging is proposed for imaging in NDE and biomedical applications. The first part of the research deals with the design of a time reversal (TR) imaging system. Unlike iterative approaches that provide a complete solution to the inverse problem, the TR based approach is non-iterative and provides a partial solution. Main advantages of the approach include faster computation time, super-resolution and selective focusing capabilities. The contribution of this research include: * Development of a model based TR algorithm for efficient target imaging without prior knowledge of background Green's function, * Design of a passive microstrip TR mirror for efficient breast tissue imaging application, * Development of a robust experimental system demonstrating its feasibility for rapid NDE of large areas of composites and breast tumor imaging. The second part of the research investigates use of probes and metamaterials for subwavelength imaging applications. The unique properties of metamaterials such as negative refractive index offer several benefits such as sub-wavelength nature, compact design and super-resolution and sub-wavelength imaging. A metamaterial lens is configured into the experimental setup to provide higher sensitivity to subwavelength defects and larger sensor to sample distance. Metamaterial inspired sensors and probes are also utilized for high resolution near field imaging of sub-wavelength features. The far field approach allows rapid scanning of large areas to detect regions of interest (ROI) with potential flaws and near field sensors are then used for scanning the ROIs to yield detailed imaging of sub-wavelength defects."--Pages ii-iii.
Read
