محمدعلي دماوندي

The first goal of this thesis has been to perform qualitative microwave imaging to detect the location and shape of hidden objects in a two-dimensional space extended along a third dimension, enclosed by an array of antennas. To achieve this, the array elements (antennas) have been positioned along the boundary of the space. For each transmitted radiation, the electric fields have been measured by all receivers in two scenarios: with and without a scatterer at the boundary of the desired space. Using the difference between these measurements—representing the scattering electric field—two proposed methods, the Conjugate of the Electric Field (CEF) and the Inverse-Multiplicative (or Reciprocal) Electric Field (REF), have been applied at a specific frequency to obtain the distribution of induced currents on the scatterers. The shape and location of the scatterers have been reconstructed using the distribution of these currents for all radiation events, avoiding computational complexity and approximations. The proposed methods have been independent of the contrast between the scatterer and the background and have also been independent of the scatterer's shape and location. It has been assumed that the scatterers are homogeneous and that the background environment is known. To validate the methods, various scenarios have been simulated using CST software, including single scatterers with circular and square cross-sections, multi-scatterer configurations, heterogeneous backgrounds, and a tumor in a brain tissue-like environment. Both PEC and dielectric scatterers with permittivity contrasts ranging from 0.5 to 67 relative to the background have been successfully reconstructed. Furthermore, a spherical tumor with a radius of 1 cm has been detected in a three-dimensional head model using the CEF method at 600 MHz. For homogeneous scatterers and backgrounds, the scatterer image has been reconstructed using electric line source theory by neglecting the array element coupling, without requiring full-wave analysis. Practical measurements have verified both proposed methods. Additionally, the use of electric line sources within the Born approximation framework has been briefly investigated. Another qualitative imaging technique, the Equivalent Search method, has been introduced to identify equivalent currents whose scattering fields closely match measured scattering fields, selecting the current distribution with minimal error. The second goal has been to achieve power focusing at a desired location in the studied environment using an antenna array at microwave frequencies. By modifying the proposed method and structure for imaging, microwave power focusing has been implemented with the same array arrangement. Therefore, two methods for power focusing have been proposed. The first method is based on optimizing a parameter defined as "focusing ability" to find the appropriate amplitude and phase of the excitation signal of the array elements. This parameter has been derived analytically from the electromagnetic power. The second method leverages the CEF technique. Both methods have been eva‎luated with examples, including fatty tissue, and validated using full-wave simulations in COMSOL and CST software. These methods have significantly reduced the time required to find excitation signals compared to full-wave approaches. Additionally, the CEF method allows power focusing with fewer array elements. Various conditions that could lead to the creation of unwanted focus points have been investigated in detail. These points have been identified as near-field unwanted lobes in power focusing. By defining the "directivity" parameter in power focusing, the focusing performance in the presence of unwanted lobes and different conditions has been examined. Finally, by optimizing the directivity parameter in an environment similar to fatty tissue with a tumor, focusing has been achieved at the tumor location. Various factors, such as noise, sensitivity, antenna type and number, coupling, environmental losses, and uniqueness, have been discussed.

تصويربرداري مايكروويو , تصويربرداري كيفي , تمركز توان مايكروويو , آرايه آنتن

Microwave Imaging , Qualitative imaging , Microwave power focusing , Antenna Array

Mohammad Ali Damavandi

Dr. Khalaj