Sharif Digital Repository

In recent years, there has been a great studying on site-specific indoor wave propagation mechanism. Conventional ray tracing method is the most common way to predict the profile of the signal in these environments. This method provides us with a deep understanding of signal propagation mechanism including reflection, refraction and diffraction. Knowing these characteristics, we can design a wireless system with optimal performance. Modified Wavefrond Decomposition Method is a ray tracing speed up technique. In this method, a bundle of rays will be traced instead of tracing single rays. If a ray bundle illuminates the receiver location, a ray that exactly crosses the receiver point would be... 

Time-varying media have been in center of attention since recent years for their plethora of applications. Achieving non-reciprocity, one-way propagation, frequency modulation, and signal amplification are some applications of such media which are accessible from microwave to optical frequencies. The aim of this thesis is to first find a method for the analysis of wave propagation in homogeneous time-varying media. To this end, a new formulation is presented based on differential transfer matrices enabling us to find amplitudes, average power, and average energy of a wave in a homogeneous time-varying medium for arbitrary temporal variation of permittivity. In addition,this formulation... 

In this thesis, we propose and discuss efficient GPU implementation using CUDA for simulating electromagnetic scattering. We use SPH as a meshless particle method to electromagnetic transient simulation in time domain. Smoothed particle hydrodynamics (SPH) has been recently reformulated by the authors, and implemented in the so-called smoothed particle electromagnetics (SPEM) method. In SPEM two set of electric and magnetic staggered particles have to be generated. These particles are the points in which the field components are computed at each time step by using the information belonging to the neighboring ones.
On the other hand, CUDA™ is a general purpose parallel computing platform... 

In this dissertation, we design and simulate Electromagnetic (EM) wave absorbers using periodic array of ultra-thin metallic ribbons, metallic disks and graphene disks based on circuit theory. The equivalent circuit for EM structures significantly eliminates the requirement of systems with advanced hardwares. Firstly, we categorize the metallic absorbers in the literature in two types: narrowband absorbers and broadband absorbers. Surface plasmon polariton, magnetic resonance, interference theory and localized surface plasmon are employed to illustrate the mechanism behind the narrowband absorption. Therefore, they will be the basis for classifying the narrowband absorbers in this work.... 

In this research, an electromagnetic wave absorber based on metamaterial structures is designed and built that is able to absorb a significant part of the wave power (up to 90%) in the millimeter wave band. The characteristics of this absorber are very low thickness (about a quarter of the wavelength compared to the central frequency) and high absorption bandwidth (up to 50% compared to the central frequency). Among the various structures studied, the structure of mesh arrays or conductive loops was selected for design. Using the Babinet principle, a transmission line model was proposed to analyze the behavior of this structure and became the basis for the design of the electromagnetic... 

Due to the gyrotropic properties of ferrites, they have the ability to create nonreciprocal structures and have been used in microwave frequencies for a long time. Despite the use of these magnetic materials in ferrite devices, circulators, antennas, insulators, etc. The investigation of wave scattering by ferrite materials has been very limited and has only been limited to finding the radar cross-section. On the other hand, metasurfaes have been the subject of many studies in recent years in order to control propagation waves and create unusual scattering (reflection or propagation) from a surface.In this thesis, electromagnetic wave scattering by a grounded ferrite disk and the phenomena...