Sharif Digital Repository

To design and identify specific properties of Metamaterials we need methods that accurately and quickly provide precise information about these composite materials for engineers. In this thesis we use FMM method with ASR technique for the analysis of Metamaterials and photonic crystals in three dimensional structures. In the second chapter FMM method is described briefly and then ASR technique for applying in the FMM method is introduced. ASR approach has large convergence rates in all types of gratings particularly metallic ones and with optimization that we have done for two dimensional periodic gratings convergence speed is increased more. In the third chapter using ASR reflection and... 

In several electro-optic and optoelectronic devices, we require the structures with simultaneous high electrical conductivity and optical transparency so as to transmit the incident light. Transparent Conductive Electrodes (TCEs) that are both highly conductive and transparent were introduced to be an answer to the mentioned challenge. Periodic arrays of metallic holes are amongst the most important structures that are used as transparent electrodes. Using the metals with low electrical resistivity, such as Au and Ag, provides these structures with high electrical conductance. On the other hand, since these micro/nano structures support the propagation of guided electromagnetic waves, light... 

A coupler free scheme for directly exited surface polariton (SP) using a negative-index metamaterial (NIMM) with a bottom layer of N type quantum emitters is presented. It is shown that by suppressing the ohmic loss the giant field enhancement could be achived in a broad electromagnetically induced transparency (EIT). And this field enhancement cause the excitation of surface polariton at the NIMM-Quantum emitter interfaces. For large range of probe detuning in EIT position and the tunable excitation of SP could be accomplished for special probe angle.It is revealed that the linear and nonlinear optical properties could be controlled effectively by modulating the phase of the microwave... 

The properties of metamaterials can be tailored through modification of their microstructures geometry. In this regard, a vast range of metamaterials have been designed. Auxetic metamaterials are a novel class of materials exhibiting the interesting characteristic of negative Poisson’s ratio. Theoretically, auxetic metamaterials have improved mechanical properties such as shear modulus and fracture toughness. The design and modeling of auxetic metamaterials is not completed yet. In order to exploit the interesting properties of auxetic metamaterials, their potential applications have been investigated in medical, sports, automobile and defense industries, so far. In the present work, the... 

Terahertz waves have three important features that make them suitable for security imaging. 1. THz waves can penetrate or can be absorbed from many of non-metallic and non-polar materials and are perfectly reflected from most of the metals, 2. Drugs and explosives have terahertz spectra that can be detected by THz imaging, 3. THz waves do not have an ionizing effect and are harmless to the human body. Lenses can be considered as a major component of the terahertz imaging systems. Because of the relatively large terahertz wavelengths compared with wavelengths, compression, and decreasing the dimensions of the lenses in these systems matters a lot. In addition, reducing the wave reflection... 

Antenna arrayss have long been utilized in many applications including communication, radar, and imaging. With the advancement of the telecommunication industry and the emergence of new requirements in the fifth generation of telecommunications, imaging and the Internet of Things, new antenna arrays are designed at higher operating frequencies and with particular specifications. One of the major challenges in using these types of antennas is unwanted mutual coupling in these systems. These couplings can occur between the antenna elements of the array itself, or between two or more arrays that are adjacent to each other. These couplings can seriously affect the performance of the system.... 

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... 

In this thesis we introduce line wave. Which propagates only in one direction and dissipate in other direction. Line wave can propagates at the interface of two complementary impedance surfaces. There are various ways to build a waveguide which can support line waves like complementary structures. In this thesis we try to find a way which will not use complementary structures. Hence we use Spoof Surface Plasmon Polariton concept to mimic complementary structure characteristics. A complementary surface-based waveguide consists of two parts; one part supports TE polarization waves and the other one supports TM polarization waves. When these TE and TM waves face each other in the boundary, line... 

Electromagnetic metamaterials are designed artificial materials with sub-wavelength resonant inclusions. They can exhibit extraordinary properties such as negative permittivity, negative permeability, and anomalous reflection/refraction. Metasurfaces are 2D counterparts of metamaterials. Here, we proposed a framework for the multiscale multiphysics analysis of deformable metasurfaces. Nonlinear mechanical analysis (Geometry and material behavior), periodic boundary conditions, homogenization, multiscale analysis, and electromagnetic analysis are implemented in this framework. Benefiting from the framework, we proposed a multifunctional hyperelastic structured surface that can generate... 

Millions of people due to factors such as osteoporosis, aging, sports incidents, and accidents face complications from bone fracture injuries every year. Nitinol shape memory alloy and Gyroid metamaterial have attracted researchers to use them as suitable replacements to fill empty areas of broken bones. In this research, numerical modeling and additive manufacturing were used to take advantage of the special properties of both nitinol and gyroid structures. In the modeling section, finite element modeling of the superelastic effect and the one-way shape memory effect of sheet and solid gyroids in cubic and cylindrical geometries with different porosities were done. As a result of the... 

Epsilon-near-zero media have attracted considerable attention in the last decade due to their exceptional behavior in wave propagation. The purpose of this research project is to analyze time-periodic ENZ structures. To this end, layered structures consisting of plasmonic metal and dielectric layers are used to achieve the epsilon-near-zero effect in a specific frequency range, and by time-variations of the dielectric layers, an effective time-varying (TV) ENZ is achieved. A method based on transfer matrix method is developed to analyze such structures while they are undergoing time-variations, and primarily under normal incident waves. Various structures based on such TV layered structures... 

As humans age, the intervertebral discs in the spine lose some of their water content, reducing their flexibility and making them more prone to tears in the annulus fibrosus. When the annulus fibrosus weakens, the disc's nucleus can push through and cause a herniation, which can press on surrounding nerves and lead to severe pain. Each surgical method for treating disc herniation has its own complications and challenges. The gold standard treatment is fusion surgery, which fixes two vertebrae together, preventing natural movement in that part of the spine. This altered stress distribution on adjacent vertebrae can ultimately damage adjacent healthy discs over time. This research aims to use...