Loading...
Search for:
polarization
0.008 seconds
Total 356 records
A Dual Polarized Planar Antenna Array for Millimeter-Wave Imaging
, M.Sc. Thesis Sharif University of Technology ; Memarian, Mohammad (Supervisor) ; Fakharzadeh Jahromi, Mohammad (Supervisor)
Abstract
Today's millimeter imaging has been widely used in the field of security and medicine. With increasing security threats, there is a need for improved security equipment. Millimetric waves not only have the ability to penetrate dielectric materials, but also the ability to separate them to detect hazardous materials. Also, the millimeter-field imagery is capable of detecting different materials from each other, which is an advantage in detecting hidden cases. Unlike X-ray imaging, millimeter waves do not have the ability to ionize the cells of the body, which reduces the risk of creating radios for imaging. In this project, an array antenna with two orthogonal poles is designed. Macrostrip...
Viral infected cells reveal distinct polarization behavior; a polarimetric microscopy analysis on HSV infected Vero and HeLa cells
, Article Journal of Quantitative Spectroscopy and Radiative Transfer ; Volume 262 , 2021 ; 00224073 (ISSN) ; Abedini, M ; Badieyan, S ; Vaezjalali, M ; Akhavan, O ; Sasanpour, P ; Sharif University of Technology
Elsevier Ltd
2021
Abstract
The optical polarization properties of virus-infected cells have been measured, analyzed, and compared with the uninfected cells. In this regard, Vero and HeLa cells have been used as the host for Herpes simplex viruses (HSV). By using polarization microscopy imaging technique, the Mueller matrix images of infected and uninfected cells have been recorded. Through image processing and further analysis, the polarization properties of host cells are compared with their infected ones. For quantitative analysis, the multispectral Mueller matrix transformation (MMT) parameters (A and b) are calculated to identify the microstructural differentiations between uninfected and infected cells by HSV....
Analysis of the Effect of Polarization in Millimeter Wave Standoff Imaging
, M.Sc. Thesis Sharif University of Technology ; Ahmadi Boroujeni, Mehdi (Supervisor)
Abstract
The basis of this research is the use of millimeter wave frequency band, due to its unique features for standoff imaging. The millimeter wave standoff system used in this thesis faces challenges such as sensitivity to change of angle, separation of the object from the background and the inability of the system to accurately detect the edges of the object, that the purpose of defining this project is to provide solutions and their feasibility with imaging system to minimize these challenges. For this purpose, first the imaging process of the system is generally simulated by two methods of physical optics/physical theory of diffraction and equivalence method and then for different conditions...
Corrosion behaviour of Ni-Co alloy coatings at Kish Island (marine) atmosphere
, Article Bulletin of Materials Science ; Vol. 37, issue. 3 , May , 2014 , p. 713-719 ; Ghorbani, M ; Sharif University of Technology
Abstract
In this study, the corrosion behaviour of Ni-Co alloys with low Co content, electroplated on steel substrate in sulphate bath, was investigated. The morphology of coatings was studied by optical and SEM microscopy. The corrosion products were analyzed using EDX. The results showed that Ni-1%Co coatings had a better corrosion resistance 0.30, 0.92 and 3.75 mpy for atmospheric, salt spray and polarization tests, respectively. These are 0.41, 1.20 and 5.40 mpy for pure nickel coatings that indicate the least corrosion resistance. Surface analysis revealed the presence of oxides, sulphides and chlorides in corrosion products
A combined model for large scale batch culture MFC-digester with various wastewaters through different populations
, Article Bioelectrochemistry ; Volume 106 , December , 2015 , Pages 298-307 ; 15675394 (ISSN) ; Yaghmaei, S ; Mardanpour, M. M ; Sharif University of Technology
Elsevier
2015
Abstract
In this study, a new model of microbial fuel cell (MFC) was obtained for the first time. The modeled MFC was made using a combination of two approaches; the conduction-based method and two-step anaerobic digestion. Performance of the MFC was based on calculations for current evolution and polarization curves with different subsequent variables of the biofilm and anolyte. The model was able to make predictions for performance of the MFC for a simple substrate to more complex ones. The model was successfully validated with a variety of substrates (acetate, glucose and dairy wastewater) and the results were compared with previously published measurements. The model polarization results showed...
Thermally induced spin-dependent current based on Zigzag Germanene Nanoribbons
, Article Physica E: Low-Dimensional Systems and Nanostructures ; Volume 86 , 2017 , Pages 175-183 ; 13869477 (ISSN) ; Faez, R ; Sharif University of Technology
Elsevier B.V
2017
Abstract
In this paper, using first principle calculation and non-equilibrium Green's function, the thermally induced spin current in Hydrogen terminated Zigzag-edge Germanene Nanoribbon (ZGeNR-H) is investigated. In this model, because of the difference between the source and the drain temperature of ZGeNR device, the spin up and spin down currents flow in the opposite direction with two different threshold temperatures (Tth). Hence, a pure spin polarized current which belongs to spin down is obtained. It is shown that, for temperatures above the threshold temperature spin down current increases with the increasing temperature up to 75 K and then decreases. But spin up current rises steadily and in...
Adopting image theorem for rigorous analysis of a perfect electric conductor–backed array of graphene ribbons
, Article Journal of the Optical Society of America B: Optical Physics ; Volume 35, Issue 8 , 2018 , Pages 1836-1844 ; 07403224 (ISSN) ; Abdolali, A ; Khavasi, A ; Rajabalipanah, H ; Sharif University of Technology
OSA - The Optical Society
2018
Abstract
Analytical and numerical study of graphene ribbons has become a prime focus of recent research due to their potential applications in tunable absorption, wavefront manipulation, polarization conversion, and so on. In this paper, an accurate analysis of a perfect electric conductor (PEC)–backed array of graphene ribbons (PAGR) is presented based on the well-known electromagnetic (EM) image theorem, where the induced currents are theoretically derived under a transverse-magnetic-polarized incident wave. For the first time, the proposed analysis rigorously incorporates the EM coupling effects between the PEC back plate and the subwavelength array of graphene ribbons. It is proved that the...
Ferrite-based wideband circularly polarized microstrip antenna design
, Article ETRI Journal ; Volume 41, Issue 3 , 2019 , Pages 289-297 ; 12256463 (ISSN) ; Komjani, N ; Rejaei, B ; Ghalibafan, J ; Sharif University of Technology
John Wiley and Sons Inc
2019
Abstract
In this paper, a wideband, circularly polarized patch antenna is proposed that leverages the unidirectional resonant modes of a circular patch mounted on top of a grounded dielectric-ferrite substrate. The proposed antenna is fed via the proximity coupling method and several parasitically coupled patches are placed on a dielectric superstrate to enhance the impedance bandwidth of the antenna. The resonant modes of the structure rotate only in the clockwise or counter clockwise directions. In the frequency range where the effective permeability of the ferrite layer is negative, the resonance frequencies of these modes differ significantly, which produces a large axial ratio (AR) bandwidth....
A compact polarization insensitive all-dielectric metasurface lens for Gaussian to tophat beam shaping in sub-terahertz regime
, Article Optics Communications ; Volume 462 , 2020 ; Ahmadi Boroujeni, M ; Tehranian, A ; Sharif University of Technology
Elsevier B.V
2020
Abstract
In this paper, we present a Gaussian to tophat beam shaper (GTBS) based on an all-dielectric metasurface lens for sub terahertz (sub-THz) applications. In order to calculate the required phase profile of the GTBS, we use an analytical procedure based on the geometrical transformation technique. The calculated phase profile is then realized by a silicon (Si) metasurface lens consisting of rectangular-shaped pillars of subwavelength dimensions. Because of large solution domain relative to the operation wavelength, we combined the beam envelope and the finite element methods to simulate the structure with a high precision. By designing an anti-reflection metasurface made up of periodically...
Reciprocal metasurfaces for on-axis reflective optical computing
, Article IEEE Transactions on Antennas and Propagation ; Volume 69, Issue 11 , 2021 , Pages 7709-7719 ; 0018926X (ISSN) ; Rajabalipanah, H ; Rahmanzadeh, M ; Abdolali, A ; Achouri, K ; Asadchy, V. S ; Fleury, R ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2021
Abstract
Analog computing has emerged as a promising candidate for real-time and parallel continuous data processing. This article presents a reciprocal way for realizing asymmetric optical transfer functions (OTFs) in the reflection side of the on-axis processing channels. It is rigorously demonstrated that the presence of cross-polarization exciting normal polarizabilities (CPENPs) of a reciprocal metasurface circumvents the famous challenge of Green's function approach in implementation of on-axis reflective optical signal processing while providing dual computing channels under orthogonal polarizations. Following a comprehensive theoretical discussion and as a proof of concept, an all-dielectric...
Phase-only femtosecond optical pulse shaping based on an all-dielectric polarization-insensitive metasurface
, Article Optics Express ; Volume 29, Issue 22 , 2021 , Pages 36900-36914 ; 10944087 (ISSN) ; Tehranian, A ; Salehi, J. A ; Sharif University of Technology
The Optical Society
2021
Abstract
Recently, metasurfaces capable of manipulating the amplitude and the phase of an incident wave in a broad frequency band have been employed for femtosecond optical pulse shaping purposes. In this study, we introduce a phase-only pulse shaper based on an all-dielectric CMOS-compatible polarization-insensitive metasurface, composed of Si nano cylinders sitting on a fused silica substrate. The required phase profile of the metasurface for desired waveforms are calculated using an iterative Fourier transform algorithm, and the performance of the pulse shaper metasurface in implementing the phase masks was assessed using full-wave simulations. Such approach for realizing a...
Phase-only femtosecond optical pulse shaping based on an all-dielectric polarization-insensitive metasurface
, Article Optics Express ; Volume 29, Issue 22 , 2021 , Pages 36900-36914 ; 10944087 (ISSN) ; Tehranian, A ; Salehi, J. A ; Sharif University of Technology
The Optical Society
2021
Abstract
Recently, metasurfaces capable of manipulating the amplitude and the phase of an incident wave in a broad frequency band have been employed for femtosecond optical pulse shaping purposes. In this study, we introduce a phase-only pulse shaper based on an all-dielectric CMOS-compatible polarization-insensitive metasurface, composed of Si nano cylinders sitting on a fused silica substrate. The required phase profile of the metasurface for desired waveforms are calculated using an iterative Fourier transform algorithm, and the performance of the pulse shaper metasurface in implementing the phase masks was assessed using full-wave simulations. Such approach for realizing a...
Electronic polarization effects on membrane translocation of anti-cancer drugs
, Article Physical Chemistry Chemical Physics ; Volume 24, Issue 20 , 2022 , Pages 12281-12292 ; 14639076 (ISSN) ; Lund, M ; Ejtehadi, M. R ; Sharif University of Technology
Royal Society of Chemistry
2022
Abstract
Free-energy calculations are crucial for investigating biomolecular interactions. However, in theoretical studies, the neglect of electronic polarization can reduce predictive capabilities, specifically for free-energy calculations. To effectively mimick polarization, we explore a Charge Switching (CS) model, aiming to narrow the gap between computational and experimental results. The model requires quantum-level partial charge calculations of the molecule in different environments, combined with atomistic MD simulations. Studying three different anti-cancer drug molecules with three different phospholipid membranes, we show that the method significantly improves agreement with available...
Exploiting Applications and Improving Performance of Polar Codes in Information Theory
, M.Sc. Thesis Sharif University of Technology ; Marvasti, Farrokh (Supervisor)
Abstract
The two central topics of information theory are the compression and the transmission of data. Shannon, in his seminal work, formalized both these problems and determined their fundamental limits. Since then the main goal of coding theory has been to find practical schemes that approach these limits.Polar codes, recently invented by Arıkan, are the first practical codes that are known to achieve the capacity for a large class of channels. Their code construction is based on a phenomenon called “channel polarization”.
Since the performance of polar code degrades when the block length is small, several kinds of Reed – Solomon concatenation is considered in order to improve the...
Since the performance of polar code degrades when the block length is small, several kinds of Reed – Solomon concatenation is considered in order to improve the...
Analysis of Circular Slot Antenna on a Ferrite Substrate
, M.Sc. Thesis Sharif University of Technology ; Rajaei, Behzad (Supervisor)
Abstract
Circular polarization (CP) is one of the common polarization types used in wireless systems for frequency identification (RFID), global positioning (GPS) and wireless local area networks (WLAN), since it can provide greater flexibility in orientation angle between transmitter and receiver, and better mobility and weather penetration than the linearly polarized antennas. Magnetic permeability in ferrites can be tuned by external magnetic field ; So ferrites can be good candidates for new reconfigurable CP antenna technology. In this project, we will consider circularly polarized slot antenna with a wide axial ratio beamwidth that consists of a normally magnetized ferrite substrate mounted...
Numerical Modeling of Terrestrial Planet Temperature Distribution Effect on Polar Vortex Forming: Venus Modeling
, M.Sc. Thesis Sharif University of Technology ; Darbandi, Masoud (Supervisor)
Abstract
A global rotating atmosphere with polar vortex and super rotation is simulated using a simplified Venus General Circulation Model (GCM). The polar vortex is maintained strongly by meridional circulation develops in the form of a simple Hadley cell, extending from the equator to the pole in both hemispheres and rotation terrestrial planet. Venus Total Polar Vortex Parameter (PVP) was defined like globally integrated super-rotation but at polar skullcaps (60-90 deg). Venus Polar Vortex Parameter is PVP=1.5 that’s qualitatively similar to observed polar vortex. Then with study in terrestrial planet and Titan modeling, we appointed the Polar Vortex Parameter and critical limit of Polar Vortex...
Finite-length scaling for polar codes
, Article IEEE Transactions on Information Theory ; Vol. 60, Issue. 10 , 2014 , Pages 5875-5898 ; ISSN: 00189448 ; Alishahi, K ; Urbanke, R. L ; Sharif University of Technology
Abstract
Consider a binary-input memoryless outputsymmetric channel W. Such a channel has a capacity, call it I (W), and for any R < I (W) and strictly positive constant Pewe know that we can construct a coding scheme that allows transmission at rate R with an error probability not exceeding Pe. Assume now that we let the rate R tend to I (W) and we ask how we have to scale the blocklength N in order to keep the error probability fixed to Pe. We refer to this as the finite-length scaling behavior. This question was addressed by Strassen as well as Polyanskiy, Poor, and Verdu, and the result is that N must grow at least as the square of the reciprocal of I (W)- R. Polar codes are optimal in the sense...
Electron acceleration by linearly polarized twisted laser pulse with narrow divergence
, Article Physics of Plasmas ; Volume 22, Issue 3 , 2015 ; 1070664X (ISSN) ; Golshani, M ; Sohaily, S ; Bahrampour, A ; Sharif University of Technology
Abstract
We numerically investigate the vacuum electron acceleration by a high-intensity linearly polarized twisted laser pulse. It is shown that the inherent spiral structure of a Laguerre-Gaussian laser pulse leads to improvement in trapping and acceleration of an electron to energies of the order of GeV in the off-axis case. Also, it is demonstrated that by employing a proper choice of initial injection parameters, the high-energetic electrons with very small scattering angles can be produced
Gaussian theory for spatially distributed self-propelled particles
, Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 94, Issue 6 , 2016 ; 15393755 (ISSN) ; Schimansky Geier, L ; Ejtehadi, M. R ; Sharif University of Technology
American Physical Society
2016
Abstract
Obtaining a reduced description with particle and momentum flux densities outgoing from the microscopic equations of motion of the particles requires approximations. The usual method, we refer to as truncation method, is to zero Fourier modes of the orientation distribution starting from a given number. Here we propose another method to derive continuum equations for interacting self-propelled particles. The derivation is based on a Gaussian approximation (GA) of the distribution of the direction of particles. First, by means of simulation of the microscopic model, we justify that the distribution of individual directions fits well to a wrapped Gaussian distribution. Second, we numerically...
Fractal nematic colloids
, Article Nature Communications ; Volume 8 , 2017 ; 20411723 (ISSN) ; Jagodič, U ; Mozaffari, M. R ; Ejtehadi, M. R ; Muševič, I ; Ravnik, M ; Sharif University of Technology
Nature Publishing Group
2017
Abstract
Fractals are remarkable examples of self-similarity where a structure or dynamic pattern is repeated over multiple spatial or time scales. However, little is known about how fractal stimuli such as fractal surfaces interact with their local environment if it exhibits order. Here we show geometry-induced formation of fractal defect states in Koch nematic colloids, exhibiting fractal self-similarity better than 90% over three orders of magnitude in the length scales, from micrometers to nanometres. We produce polymer Koch-shaped hollow colloidal prisms of three successive fractal iterations by direct laser writing, and characterize their coupling with the nematic by polarization microscopy and...