Sharif Digital Repository

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.... 

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... 

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... 

Metamaterials are engineered sub-wavelength structures which show electromagnetic properties not found in natural materials. There is a special interest in superconductor metamaterials in microwave engineering. These metamaterials have low loss, are compact and show useful properties like tunability and parametric amplification when Josephson junctions are incorporated in them. When Josephson junctions are used, these metamaterials are called Josephson metamaterials which have attracted a good amount of research interest. Because of nonlinear nature of Josephson junction, Josephson metamaterials show nonlinear properties. One dimensional Josephson metamaterials are called Josephson... 

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... 

In the last decade, mechanical metamaterials have attracted more attention due to new design principles that combine the concept of hierarchical architecture with material size effects at the micro or nano scale. This strategy shows extraordinary mechanical performance that we use in unknown parts of the material property space, including strength-to-density ratios, extraordinary flexibility, and the ability to absorb energy with brittle components. The aim of this research was to print metamaterial scaffolds from a combination of biocompatible and bioactive to be used as scaffolds in bone tissue engineering. In addition to the biological properties appropriate to the host tissue, the... 

At almost all frequencies, we have good methods to generate and detect electromagnetic radiations. One crucial exception is the low terahertz range,where despite intensive research there is a severe lack of proper devices for many applications in this frequency range such as oscillators and detectors that is so-called THz gap and includes 0.3 to 10 THz spectrum. There are different types of THz detectors but bandwidth of dection of most of them is narrow. Among these detectors, superconducting transition edge balometer detector has detectivity in wide frequency range. But generally, detectivity of these detectors strongly depends on their ability to absorb radiations of electromagnetic waves...