Sharif Digital Repository

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 research, diffraction limit is introduced as the major challenge in wave focusing. Common wave focusing techniques have been reviewed and classified into two categories: far-field and near-field techniques. Through examples that illustrate its major inherent and practical challenges, super-oscillation has been presented as a specific idea of focusing waves using remote sources. By introducing subwavelength inhomogeneities in the region of interest, we have demonstrated sub-diffraction wave focusing in a near-field approach. Using the multipole method, the effect of injecting sub-wavelength cylindrical particles on focusing electromagnetic waves has been studied. Since when there are... 

This dissertation focuses on addressing electromagnetic forward and inverse scattering problems using physics-based deep learning models. A key challenge in integrating physics with data-driven models lies in the implicit nature and nonlinearity of the forward scattering operator. To address this, a novel closed-form expression is proposed for piecewise homogeneous media. By formulating the scattered field as an implicit function of the permittivity values in each homogeneous region, the computational complexity of solving the forward problem for a fixed geometry is changed from O(N^3 ) to O(NΣM_k^2), where N is the total number of meshes, and M_k refers to the meshes in the kth region. This... 

This dissertation introduces a method for reducing errors in prior information related to the actual geometry of biological tissues in microwave imaging. These errors, often caused by boundary mismatches or inaccurate modeling of tissue heterogeneity, significantly impact the accuracy of retrieved tissue dielectric properties. To address this issue, we propose a shape optimization-based approach that aligns prior boundary data with actual tissue boundaries using measured microwave imaging data. Our method features an efficient technique for computing the sensitivity of scattered electric fields to node positions. By deforming the mesh structure without altering its topology, this approach... 

Electromagnetic wave scattering from rough surfaces has been the subject of intensive investigations over the past several decades for its applications in important remote sensing problems. The problem of scattering from random rough surfaces hasn't full analytical closed form solution. In millimeter-wave band some surfaces like asphalt, concrete, which has roughness in millimeter range, must be considered as rough surfaces. A major part of the literatures are specified to numerical and statistical approach. In this thesis the electromagnetic waves scattering from rough surfaces in millimeter-wave band is studied. The main goal of this thesis is to find the available ways for applying the... 

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... 

In this dissertation, hybrid meshless method for electromagnetic wave scattering has been presented. The idea of the dissertation is the use of two robust meshless shape functions i.e. MLS and RPIM simultaneously to solve differential and integral equations from 3D scattering equations respectively. Finite element method (FEM) and method of moments (MoM) are used extremely for computing scattering problems. These methods are powerful and their results are accurate enough. One of their disadvantages is the need of mesh generation. Mesh generation in FEM is a time consuming process. Furthermore, in electromagnetic problems that involve geometrical, the use of an underlying mesh creates... 

In this dissertation, site-specific ultrawideband propagation modeling has been presented based on ray tracing. The empirical, statistical and site-specific methods are compared and the ray tracing method is selected as an efficient and accurate site-specific approach for indoor propagation modeling. The challenges of the ray tracing method in propagation modeling of ultrawideband electromagnetic waves are outlined and some solutions are presented.In order to increase the efficiency of finding the propagation paths, the modified wavefront decomposition method is presented. This method intelligently reduces the number of emitted rays and finds the exact propagation paths from the transmitter... 

Always, there has been a great interest toward electromagnetic wave propagation and new ways for simulation of the problem. Level set methods provide a powerful mathematical framework for propagating surfaces (in 3-D) or curves (in 2-D). The contours of the moving objects are viewed as the zero level sets of a function and propagated in a Eulerian point of view by means of a Hamilton–Jacobi partial differential equation expressing the conservation of the level sets under a given velocity field. Level set methods have been applied in a wide range of domains, such as physics, chemistry, fluid dynamics, combustion, image processing… In this thesis, we introduce a new numerical procedure for... 

Nowadays, wireless communication plays a key role in everyday lives and has many different applications. Today’s communication systems require high bandwidths in order to transfer data with higher bitrates. Among these, modeling a wireless channel is one of the most important challenges in wireless communications. Modeling an indoor Ultra-Wide-Band (UWB) wireless channel has been involved in a great number of researches. In order to model a UWB channel, we need to correctly investigate electromagnetic waves inside the buildings. Amongst different methods that are used for this aim, ray tracing method is one of the most accurate and fast ones. In this thesis, time-domain reflection and...