Electromagnetic (EM) imaging schemes are inherently non-linear and ill-posed. Albeit there exist remedies to these fundamental problems, more efficient solutions are still being sought. To this end, in this thesis, the non-linearity is tackled in- corporating a multitude of techniques (ranging from Born approximation (linear), inexact Newton (linearized) to complete nonlinear iterative Landweber schemes) that can account for weak to strong scattering problems. The ill-posedness of the EM inverse scattering problem is circumvented by formulating the above methods into a minimization problem with a sparsity constraint. More specifically, four novel in- verse scattering schemes are formulated and implemented. (i) A greedy algorithm is used together with a simple artificial neural network (ANN) for efficient and accu- rate EM imaging of weak scatterers. The ANN is used to predict the sparsity level of the investigation domain which is then used as the L0 - constraint parameter for the greedy algorithm. (ii) An inexact Newton scheme that enforces the sparsity con- straint on the derivative of the unknown material properties (not necessarily sparse) is proposed. The inverse scattering problem is formulated as a nonlinear function of the derivative of the material properties. This approach results in significant spar- sification where any sparsity regularization method could be efficiently applied. (iii) A sparsity regularized nonlinear contrast source (CS) framework is developed to di- rectly solve the nonlinear minimization problem using Landweber iterations where the convergence is accelerated using a self-adaptive projected accelerated steepest descent algorithm. (iv) A 2.5D finite difference frequency domain (FDFD) based in- verse scattering scheme is developed for imaging scatterers embedded in lossy and inhomogeneous media. The FDFD based inversion algorithm does not require the Green’s function of the background medium and appears a promising technique for biomedical and subsurface imaging with a reasonable computational time. Numerical experiments, which are carried out using synthetically generated mea- surements, show that the images recovered by these sparsity-regularized methods are sharper and more accurate than those produced by existing methods. The methods developed in this work have potential application areas ranging from oil/gas reservoir engineering to biological imaging where sparse domains naturally exist.

The driving force behind this thesis was the need for developing tissue mimicking materials that can mimic the dielectric properties of various biological soft tissues to aid in the development and testing of electromagnetic medical devices. Materials that can mimic the dielectric properties of human skin, adipose, muscle, malignant and healthy fibroglandular tissue, liver, pancreas, and kidney within the frequency range of 500 MHz to 20 GHz have been characterized and tested. The tissue mimicking materials are used to construct biological phantoms for studies that involve the investigation of wireless medical telemetry and a microwave breast cancer detection device.

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Yes / An ultra-wideband microstrip antenna design is considered with respect to applications in breast cancer detection. The underlying design concept is based on ground penetrating radar (GPR). Simulated and measured prototype performance show excellent performance in the input impedance and radiation pattern over the target range from 4 GHz to 8 GHz. The 4 GHz to 8GHz frequency band for microwave imaging perform better in comparison with other microwave frequencies. The antenna also shows a reasonable uniform radiation performance in the broadside direction which contributes to the reduction of clutter levels, thus aiding the reconstruction quality of the final image.

Yes / In this article, a novel uniplanar ultra‐wideband (UWB) stop frequency selective surface (FSS) was miniaturized to maximize the gain of a compact UWB monopole antenna for microwave imaging applications. The single‐plane FSS unit cell size was only 0.095λ × 0.095λ for a lower‐operating frequency had been introduced, which was miniaturized by combining a square‐loop with a cross‐dipole on FR4 substrate. The proposed hexagonal antenna was printed on FR4 substrate with coplanar waveguide feed, which was further backed at 21.6 mm by 3 × 3 FSS array. The unit cell was modeled with an equivalent circuit, while the measured characteristics of fabricated FSS array and the antenna prototypes were validated with the simulation outcomes. The FSS displayed transmission magnitude below −10 dB and linear reflection phase over the bandwidth of 2.6 to 11.1 GHz. The proposed antenna prototype achieved excellent gain improvement about 3.5 dBi, unidirectional radiation, and bandwidth of 3.8 to 10.6 GHz. Exceptional agreements were observed between the simulation and the measured outcomes. Hence, a new UWB baggage scanner system was developed to assess the short distance imaging of simulated small metallic objects in handbag model. The system based on the proposed antenna displayed a higher resolution image than the antenna without FSS.

<p>Microwave imaging is a promising new imaging modality under research for breast cancer detection. This technique images/reconstructs the internal dielectric composition of the breasts and relies on the contrast between the dielectric properties of malignant tissues and healthy tissues to pinpoint the abnormality. Over the years, new imaging algorithms were proposed and many imaging systems were developed in accordance. However, none of the proposed systems has made it to the market.</p> <p>In this thesis, a prototype planar raster-scanning system for near-field microwave imaging is presented. This system measures the scattering parameters while scanning a 2-D plane over the imaged object (phantom) in a raster pattern. The development of this system aids significantly in our research of microwave imaging for breast cancer detection because it enables us to carry out numerous experiments and to develop and verify new imaging algorithms.</p> <p>Our contribution also lies in conducting a comprehensive study of the dynamic range of the developed system. Each source of noise/uncertainty from the system is identified and studied for the benefits of future improvements.</p> <p>Typical imaging results of phantoms with different dielectric properties are also provided to showcase the performance of the developed system.</p> / Master of Applied Science (MASc)

<p>Accurate knowledge of the frequency- and temperature-dependent dielectric properties of biological tissues is crucial in the development of ultra-wideband diagnostic and therapeutic technologies such as microwave breast cancer detection and hyperthermia treatments. This work examines the temperature dependence of the dielectric properties of the five tissue phantom-types developed by our group as well as porcine fat, muscle and liver tissues for the frequency range from 3 GHz to 10 GHz and for the temperature range from 5 °C to 45 °C. A systematic and simple measurement procedure is developed to measure the continuous temperature dependence of the dielectric properties of the various phantom and tissue types. The temperature trends of the dielectric properties of the different phantoms and tissues are investigated.</p> <p>Linear temperature coefficients at discrete frequencies are impractical and insufficient in ultra-wideband applications when realistic, non-linear numerical models of the dielectric properties are required. Therefore, a compact one-pole Cole-Cole model is used to model the frequency dependence of the dielectric properties of the measured samples at every temperature point. A second- or third-order polynomial is used to model the temperature dependence of the Cole-Cole parameters. The final model is a one-pole Cole-Cole model whose parameters are polynomial functions of temperature. This model enables the estimation of the relative permittivity and the conductivity of the measured phantom and tissue types at any temperature and frequency.</p> / Master of Applied Science (MASc)

<p>This thesis contributes significantly to the advanced applications of scattering parameter sensitivity analysis including the design optimization of high-frequency printed structures and in microwave imaging. In both applications, the methods exploit the computational efficiency of the self-adjoint sensitivity analysis (SASA) approach where only one EM simulation suffices to obtain both the responses and their gradients with respect to the optimizable variables.</p> <p>An<em> S</em>-parameter self-adjoint sensitivity formula for multiport planar structures using the method of moments (MoM) current solution is proposed. It can be easily implemented with existing MoM solvers. The shape perturbation which is required in computing the system-matrix derivatives are accommodated by changing the material properties of the local mesh elements. The use of a pre-determined library system matrix further accelerates the design optimization because the writing/reading of the system matrix to/from the disk is avoided. The design optimization of a planar ultra-wide band (UWB) antenna and a double stub tuner are presented as validation examples.</p> <p>In the application of the sensitivity-based imaging, the SASA approach allows for real-time image reconstruction once the field distribution of the reference object (RO) is known. Here, the RO includes the known background medium of the object under test (OUT) and the known antennas. The field distribution can be obtained using simulation or measurement.</p> <p>The spatial resolution is an important measure of the performance of an imaging technique. It represents the smallest detail that can be detected by a given imaging method. The resolution of the sensitivity-based imaging approach has not been studied before. In this thesis, the resolution limits are systematically studied with planar raster scanning and circular array data acquisition. In addition, the method’s robustness to noise is studied. A guideline is presented for an acceptable signal-to-noise ratio (SNR) versus the spatial and frequency sampling rates in designing a data-acquisition system for the method.</p> <p>This thesis validates the sensitivity-based imaging with measured data of human tissue phantoms for the first time. The differences in dielectric properties of the targets are qualitatively reflected in the reconstructed image. A preliminary study of imaging with inexact background information of the OUT is also presented.</p> / Doctor of Philosophy (PhD)

SMOS (Soil Moisture and Ocean Salinity) is ESA's Earth Explorer series satellite carrying the novel MIRAS (Microwave Imaging Radiometer with Aperture Synthesis) interferometric synthetic aperture radar. Its objective is monitoring and studying the planet's water cycle by following the changes in soil moisture levels and ocean surface salt concentrations on a global scale. The success of the mission calls for nearly uninterrupted operation of the science payload. However, the instrument experiences sporadically problems with its hardware, which cause losses of scientific data and may require intervention from ground to resolve. The geographical areas in which most of these anomalies occur, polar regions and the South-Atlantic anomaly, give cause to assume these problems are caused by charged particles in the planet's ionosphere. In this thesis, methods of predicting occurrence of hardware anomalies from indicators of Earth radiation environment are investigated.

Ces travaux portent sur le développement d'une technique de compression appliquée à la simplification des systèmes d'imagerie dans le domaine microonde. Cette approche repose sur le développement de composants passifs capables de compresser les ondes émises et reçues, autorisant ainsi une réduction du nombre de modules actifs nécessaires au fonctionnement de certaines architectures de radars. Ce principe est basé sur l'exploitation de la diversité modale présente dans les composants développés, le rendant compatible avec l'utilisation de très larges bandes passantes. Plusieurs preuves de concept sont réalisées au moyen de différents composants étudiés dans cet ouvrage, permettant d'adapter cette technique à de nombreuses spécifications d'architectures et de bandes passantes. / This work is focused on the development of a compressive technique applied to the simplification of microwave imaging systems. This principle is based on the study of passive devices able to compress transmitted and received waves, allowing for the reduction of the hardware complexity required by radar systems. This approach exploits the modal diversity in the developed components, making it compatible with ultra wide bandwidth. Several proofs of concept are presented using different passive devices, allowing this technique to be adapted to a large variety of architectures and bandwidths.