Detection of cancerous tumors in biological tissues using microwave imaging

dissertation for obtaining a master's degree

in the field of electrical engineering field telecommunications

abstract

This thesis is about the applications and development of time-reversal techniques based on signal processing methods for broadband electromagnetic waves in homogeneous and discrete random environments and It is constantly focused. Time reversal methods based on the invariance of Maxwell's equations under the condition of reversal of its time component are one of the suitable and significant techniques for imaging. With the increase of heterogeneity and multiple scattering in the environment, the accuracy of these techniques increases. Due to the success of the time reversal technique in sound waves, there has been a lot of interest in using the Time Reversal method with electromagnetic waves in radio frequency. In this thesis, firstly, the high resolution of time-reversed UWB electromagnetic wave focus will be investigated in the continuous random background environment of the first and second type. Also, two DORT and TR-MUSIC techniques, which are high-resolution imaging methods for detecting and locating hidden targets in homogeneous and heterogeneous environments, are introduced from the ground up, coded and implemented in the FDTD numerical laboratory, and the effective parameters of these techniques are evaluated. The performance of these two techniques in microwave imaging in a random heterogeneous environment including point scatterers is shown. The considered random heterogeneous environment is based on spatial changes of soil permeability. The effect of the parameters of a random heterogeneous environment on the eigenvalues ??and eigenvectors of the time inverse operator for two close targets will be investigated. In the following, we will add a special and practical aspect to the problem of microwave imaging using the TR-MUSIC technique in general and direct it to the problem of "imaging from behind the wall". Polarization effects are simulated and analyzed using this technique in this applied example, and it is also shown that this technique gives acceptable results even for the case where the wall has severe losses. Finally, the tracking of the target behind the wall will be addressed using the TR-MUSIC technique.

Keywords

Microwave imaging, DORT and TR-MUSIC techniques, continuous random environment, polarization, positioning of the target behind the wall.

Electromagnetic imaging

Electromagnetic imaging using radio frequency (RF), microwave or optical signals has always been used as a diagnostic tool due to its unique characteristics. Electromagnetic imaging has attracted a lot of attention and therefore extensive research has been done in this field, the reason for which is the diversity and suitability of this imaging method for its wide applications. For example, microwave imaging (MWI) [1] has been used in non-destructive testing (NDE) [2] to detect defects in materials and measure physical parameters [1]. It can also be used to describe materials such as determining constituents and evaluating porosity [3]. In military applications, the ability of electromagnetic waves to penetrate dielectric materials has led to their use in military interrogations [2]. In air and space applications, it is used to detect cracks on the aircraft body [3]. In the field of geographical exploration, MWI is used in remote sensing to identify tunnels, landfill remains, and unexploded underground mines [4]. In civil and industrial engineering applications, MWI can be useful for assessing the structural integrity of roads, buildings and bridges [5]. Currently, in a medical field, MWI systems have been presented for non-invasive biological imaging [4]. From this short and incomplete list, it is clear that the scope of electromagnetic imaging is wide and many applications can be found for it in different fields.In some of these applications, only qualitative information about the object under test is needed, while in many cases, such as demining applications [5], non-invasive archaeological survey or medical imaging, quantitative information about the target object is needed, which can be determined using dielectric properties [6]. These dielectric properties, conductivity ( ) [7] and relative permittivity ( ) [8], are determined by using the transmission, reflection and attenuation of microwave signals when passing through the object. 1-2 Microwave imaging Microwave imaging consists of directing and performing a series of electromagnetic measurements in the microwave band, on a object and then extract important parameters such as the shape and position of that object from the obtained data. Before the invention of such a method, the use of X-rays [9] was a common method in imaging invisible objects. But the resulting image using this beam is associated with errors and is also considered an invasive imaging method. In this case, the idea of ??using electromagnetic waves for imaging was proposed. The reason for using pulses with a wide bandwidth (UWB) [10] instead of single frequency signals or in a specific frequency range is to reduce the characteristic internal reflections of the objects being irradiated, in this case the use of electromagnetic waves is justified. The use of microwave imaging in various fields is increasing, but due to the weakness in providing comprehensive and practical algorithms, it still needs further development. on the application and development of time reversal (TR) based signal processing techniques for ultrawideband (UWB) electromagnetic waves in homogeneous and discrete and continuous random media. One of the suitable and considerable methods for imaging is Time-reversal techniques that exploit the invariance of the Maxwell equation under time reversal. By multiple scattering in the intervening media, refocusing resolution can be increased. With the success of initial TR experiments in acoustics, there has been a strong interest in the application of TR methods using radio frequency electromagnetic (EM) waves. In the dissertation investigate the super resolution effects of time-reversed UWB EM waves under continuous random background media and examine their dependence on the first- and second-order statistics. DORT and TR-MUSIC that are super-resolution imaging methods for locating and detecting hidden objects in complex environments, inhomogeneous, and cluttered media, are comprehensively introducing from the beginning, implementing them in FDTD - own numerical lab, and evaluating particular affecting the performance of these techniques. Furthermore, the effect of random medium statistics on the TR operator eigenvalues ??and eigenvectors for two close targets is inspected. In continuation, we add a particular and applicable aspect of TR-MUSIC based Microwave Imaging and conduct it towards the problem of "Through-Wall Microwave Imaging". The polarization of the EM waves is also analyzed to observe the depolarization effects on the refocusing of TR-MUSIC in this practical example. Also in this respect it will be shown that this technique even for the case when the wall is extremely casualties, gives acceptable results. Also in this respect will be shown that this technique even for the case when the wall is extremely casualties, gives acceptable results.

Keywords:

Microwave imaging, DORT and TR-MUSIC, continuous random environment, polarization, tracking target from behind the wall.