This thesis contributes to the solution of the inverse electromagnetic (EM) scattering problems arising in microwave imaging. A calibration technique based on measurements of specific objects is proposed and a fast quantitative imaging method based on such measurements is developed. The calibration measurements are performed on two known objects: the reference object representing the scatterer-free measurement and the calibration object representing a small scatterer embedded in the reference object. The inversion method does not need analytical or numerical approximations of the forward model as those are replaced by the measurement-based model. It is particularly valuable in short-range imaging, where analytical models of the incident field do not exist while the fidelity of the simulation models is often inadequate. In this thesis, it is demonstrated that the implementation of the calibration technique in the sensitivity-based imaging improves both the imaging efficiency as well as the image quality. A quantitative imaging method is further developed based on the calibration measurements where a direct inversion in real space is employed. The electrical properties of dielectric objects are reconstructed using a resolvent kernel in the forward model, which is extracted from the calibration measurements. The experimentally determined resolvent kernel inherently includes the particulars of the measurement setup, including all transmitting and receiving antennas. The inversion is fast, allowing for quasi-real-time image reconstruction. The theoretical limitations of the fast quantitative imaging method have been investigated and its performance with noisy data has been examined. It is found that the proposed method has limitations which are more flexible than those of the linear Born model. The method is also robust to random noise. Both the calibration technique and the fast quantitative imaging method are validated through synthetic, simulation and/or experimental examples. The proposed concept of experimentally derived resolvent kernel in the forward model is general and may be valuable in other imaging modalities such as ultrasound, photonic imaging, electrical-impedance tomography, etc. / Dissertation / Doctor of Philosophy (PhD)

No description available.

Novel characteristics of spin-based phenomena are intensively researched in the hope of discovering effects that could be used to develop new types of high-performance spintronic devices. Recent dynamics studies have revealed new principles for spintronic devices to sense microwaves. The capabilities for detecting both microwave electric field and magnetic field could make the spintronic microwave sensor as ubiquitous as semiconductor devices in microwave applications in the future. In this thesis, the feasibility of spintronic sensors in microwave applications has been researched and developed. Thanks to the high conversion efficiency of microwave rectification in the magnetic tunnel junction (MTJ) based spintronic sensor, it can directly measure the coherent spatially scattered microwave field distribution and detect a hidden object by analyzing the reflected microwave amplitude pattern. To enable the “real-time” vector measurement of the microwave field, a sensor based rapid phase detection technique is also developed. Combining the rapid phase detection technique and the microwave holography principle, a two-dimensional microwave holographic imaging system using a spintronic sensor was built. The high sensitivity of the microwave phase measurement allows the coherent imaging of the target to be reconstructed in noisy environments. By adapting the broadband measurement, not only the shape but also the distance of the target can be determined, which implies that three-dimensional imaging is achievable using a spintronic device. Combining the broadband microwave measurement and a wavefront reconstruction algorithm with a spintronic microwave sensor in circular trajectory, the reconstructed images of targets are obtained. The reconstructed images clearly indicate the targets' positions even when the targets were immersed in a liquid to simulate an inhomogeneous tissue environment. Our spintronic techniques provide a promising approach for microwave imaging, with the potential to be used in various areas, such as biomedical applications, security services, and material characterization. / October 2016

Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (leaves 174-175).

No description available.

Microwave imaging technologies have been widely researched in the biomedical field where they rely on the imaging of dielectric properties of tissues. Healthy and malignant tissue have different dielectric properties in the microwave frequency region, therefore, the dielectric properties of a human body's tissues are generally different from other contraband materials. Consequently, dielectric data analysis techniques using microwave signals can be used to distinguish between different types of materials that could be hidden in the human body, such as explosives or drugs. Other concerns raised about these particular imaging systems were how to build them cost effectively, with less radiation emissions, and to overcome the disadvantages of X-ray imaging systems. The key challenge in security applications using microwave imaging is the image reconstruction methods adopted in order to gain a clear image of illuminated objects inside the human body or underneath clothing. This thesis will discuss in detail how microwave tomography scanning could overcome the challenge of imaging objects concealed in the human body, and prove the concept of imaging inside a human body using image reconstruction algorithms such as Radon transformation image reconstruction. Also, this thesis presents subspace based TR-MUSIC algorithms for point targets and extended targets. The algorithm is based on the collection of the dominant response matrix reflected by targets at the transducers in homogenous backgrounds, and uses the MUSIC function to image it. Lumerical FDTD solution is used to model the transducers and the objects to process its response matrix data in Matlab. Clear images of metal dielectric properties have been clearly detected. Security management understanding in airports is also discussed to use new scanning technologies such as microwave imaging in the future. The main contribution of this reseach is that microwave was proved to be able to image and detect illegal objects embedded or implanted inside human body.

Breast cancer is one of the most widespread types of cancer in the world. The key factor in treatment is to reliably diagnose the cancer in the early stages. Moreover, currently used clinical diagnostic methods, such as X-ray, ultra-sound and MRI, are limited by cost and reliability issues. These limitations have motivated researchers to develop a more effective, low-cost diagnostic method and involving lower ionization for cancer detection. In this thesis, radar based microwave imaging is proposed as a method for early breast cancer detection. This imaging system has advantages such as low cost, being non- invasive and easy to use, with high image resolution and its thus good potential for early cancer detection. In the first stage, an ultra-wideband Vivaldi antenna and a slot Vivaldi antenna are proposed, simulated and fabricated for breast cancer detection. The designed antennas exhibit an ultra-wideband working frequency. The radiation patterns also achieve the desired directional radiation patterns. The second stage of this study presents a planar breast phantom and a hemisphere breast phantom. These two breast phantoms are simulated and fabricated using CST microwave studio and tissue-mimicking materials respectively. Mono-static radar systems based on a single antenna configuration and an antenna pair configuration are then proposed. These two systems are used to measure the planar breast phantom and hemi- sphere breast phantom, with the scattering signals measured in the frequency and time domains. Based on the measurement results, it is concluded that the reflected energy increases when the antenna moves close to the tumour; otherwise, the reflected energy is reduced when the antenna moves away from the tumour. The received time domain scattering signals are processed first and then used to create microwave images to indicate tumour position. A clutter removal method is proposed to extract the tumour response from the received signals. The microwave images are then created using the tumour response based on the simulation and experimental results. The imaging results indicate that a 5 mm radius tumour can be detected. The tumour burial depth is also studied. A multi bio- layer phantom which contains deep and shallow buried tumours is simulated and measured using the Vivaldi antenna. A spectrum analysis method is proposed to distinguish between different tumour depths. The results indicate that a difference in depth of 15 mm results in a mean change of 0.3 dB in the magnitude of the spectrum. Discrimination between benign and malignant tumours is also considered in this study. The singularity expansion method (SEM) for breast cancer is proposed to discriminate between benign and malignant tumours based on their morphology. Two cancerous breast phantoms are developed in CST. The benign tumour is a 5mm radius sphere and the malignant tumour is a spiny sphere with an average radius of 5mm. The use of the SEM leads to the successful discrimination of these two tumours. This method provides a solution to discriminate between benign and malignant tumours similar size when the resulting images cannot provide sufficient resolution. A preliminary study of brain cancer detection is also concluded. Research in this area has never been implemented. A cancerous brain model is designed and simulated in CST. The antenna pair configuration is then used to measure the cancerous brain, with the scattering signals measured. Microwave images for brain cancer detection are then created based on the measurement results. The tumour is correctly indicated in the resulting images.

Thesis (M.S.)--University of Missouri--Rolla, 2007. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed November 14, 2007) Includes bibliographical references (p. 118-119)

Microwave imaging creates images of electrical property distributions in tissue, and has promise for breast tumor detection due to the contrast in electrical properties of normal and malignant breast tissues and the accessibility of the breast for imaging. Confocal microwave imaging (CMI) is a recently introduced technique that avoids limitations associated with classical microwave imaging. CMI detects areas of increased scatter (e.g. tumors) by scanning the synthetic focus of an array of antennas through the breast. As the object is illuminated with ultra-wideband signals, this corresponds to computing time delays to the focal point, resulting in simple image reconstruction algorithms. Additionally, the resolution is determined primarily by the bandwidth of the illuminating signal, allowing for detection of small tumors with appropriate selection of this bandwidth. CMI appears to be a simple and effective technique for breast tumor detection. The development and evaluation of a new approach to confocal microwave imaging is the contribution of this thesis. CMI was only very recently introduced, and many key issues need to be addressed. Most importantly, the CMI system must be designed for physical compatibility with the breast examination. The previously introduced CMI system is planar, and involves placing an array of antennas directly on the naturally flattened breast (of a woman who is lying on her back). In this thesis, a cylindrical CMI configuration is developed. A woman lies on her stomach, the breast extends through a hole in the examination table, and is immersed in a low-loss material. The breast is encircled by an array of antennas, which is placed at a distance from the skin. The cylindrical configuration is likely more appropriate for clinical implementation. The development of cylindrical CMI involves design of appropriate sensing elements and development of image reconstruction algorithms. Construction of appropriate models and simulations of the system are required to test the feasibility of the proposed sensors and algorithms. The finite difference time domain (FDTD) method is well suited to these feasibility studies, as ultra-wideband signals are efficiently simulated in the time domain. In this thesis, four alternative antenna designs are characterized with measures appropriate for ultra-wideband radiation and this specific imaging application. The selected antenna is scanned in a circle around the breast and at a distance from the skin. This is repeated for a number of rows at different heights in order to synthesize a cylindrical or conical array. The returns recorded at each antenna location are processed to reduce clutter, then synthetically focussed at points in the domain of interest. Results indicate that the proposed antenna and algorithms provide the capability to detect and localize (in three dimensions) small spherical tumors at reasonable depths in the breast models. The detection capability achieved with the cylindrical system is comparable to that obtained with the previously introduced planar system. / Graduate

Microwave imaging has been used to observe optically obscured targets for over 40 years. Recently, there has been a push towards developing a microwave imaging technology for use in medical diagnostics. Microwave imaging technology has several advantages over current imaging modalities, including use of nonionizing radiation, and compact inexpensive electronics. However, no microwave diagnostic technology exists yet for clinical use. This is due to complications in estimating the complex near-field scattering of the microwave radiation. Recently, advancements in a direct inversion algorithm known as microwave holography have adapted it to operate on near-field measurements. This method, with simulations, has demonstrated the ability to estimate the relative permittivity of the imaged structures. The purpose of this work is to develop quantitative microwave holography for use in tissue imaging. In addition to the previous version of quantitative microwave holography using the Born approximation, a new version of the method using Rytov's approximation is derived, expanding the versatility of the algorithm. Filtering strategies are also developed to enhance the image-reconstruction quality. However, nonphysical permittivity values are still generated. One possible solution is a constrained optimization strategy, which is derived and implemented. Finally, experimental studies demonstrate the ability of quantitative microwave holography to produce reconstructions of several tissue phantoms. / Thesis / Master of Applied Science (MASc)