Sharif Digital Repository

Terahertz (THz) spectroscopy has recently attracted great interest due to the special characteristics of THz waves, such as their capability of penetrating and passing through many non-polar materials, non-ionizing atoms and especially human tissues, and less scattering compared to optical waves and X rays. Also, polar molecules of some dielectric materials have vibrational or circular oscillations that create peaks in their spectral characteristics. This can be used to identify materials by spectroscopy. In this thesis, a simple THz spectroscopy system is introduced and modeled for detecting the C-4 material. First, a wideband Vivaldi antenna is designed and simulated for the frequency... 

The colloidal crystals are formed of spherical particles and can be fabricated using simple and low-cost chemical methods. Optical properties of colloidal crystals should be recognized properly in order to design optical devices based on these nano-structures. Reflection and transmission coefficients of these multilayer structures are very important for understanding their properties. Semi-analytical methods like Fourier Modal method (FMM) can be very useful to obtain their reflection and transmission properties of these multilayer structures. In this thesis, we try to implement Matched Coordinate (MC) and Adaptive Spatial Resolution (ASR) techniques in the FMM. These techniques increase... 

Production logging consists of running measurement instruments called logging tools into an oil or gas well to measure various parameters such as temperature, flow velocity, pressure, density, etc. The primary purpose for production logging is to allow enhancing production profits and decreasing costs. Nowadays the common way for fluid density measurement as a part of these tools depends on radioactive source. Special considerations must be taken upon the use of this principle due to its radioactive character. This thesis is focused on a non-radioactive method of determining density. The subject of this thesis is to consider methods for measuring density based on principle of acoustic... 

Structures that change color in an adjustable way have been noticed in recent years. There are structures in nature such as the skin of chameleons and octopuses and other animals that can change color. In recent years, inspired by these structures, materials based on photonic crystals or surface plasmonics have been proposed to change color. In this research, a review is made on these structures in nature as well as recent efforts to make such materials. In fact, photonic crystals create a special color due to the interference between scattered waves. For example, the change in the distance between the nanoparticles in the photonic crystals inside the chameleon skin is the cause of its color... 

One of the different sensing techniques for biosensors is based on surface plasmon resonance which provides high reliability and efficiency. In this project working operating principles of biosensors based on surface plasmon resonance will be examined. For investigation of sensing meachanism we assume that there an array consisting of alternating graphen ribbons which by applying light leads to an effective magnetic field coupling to the localized surface plasmon. The numerical calculations are based on the exact solution of Maxwell's equation using Fuorier Model Method and Matlab coding. In these calculations, the coefficients of transmission, reflection and absorption of light versus... 

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... 

Nonlinear transmission line (NLTL) a guiding structure contains nonlinear elements. For discrete NLTLs, this structure is periodically loaded with nonlinear elements. In the structure of this line nonlinear elements such as ceramic capacitors, nonlinear magnetic elements, vector diodes, Mos transistors, etc can be used. With the rapid development of semiconductor devices and microwave band systems, the demand for implementation of NLTLs has increased. These lines provide wide band-width, cut-off frequencies over the hundreds of GHz and picosecond rise time for various systems.Among the applications of NLTL, the generation of high power RF pulses has attracted the most attention. In this...