Search for: fourier-transforms
Total 604 records
Article Sampling Theory in Signal and Image Processing ; Volume 7, Issue 2 , 1 May , 2008 , Pages 109-112 ; 15306429 (ISSN) ; Sharif University of Technology
Tunable delay line based on Fourier-transformation and linear phase modulation with high time-bandwidth product, Article Photonische Netze - 13. ITG-Fachtagung 2020 ; 2020 , Pages 229-231 ; Preubler, S ; Jamshidi, K ; Akbari, M ; Schneider, T ; Sharif University of Technology
VDE Verlag GmbH 2020
We recruit basic properties of Fourier transformation to realize an electrically tunable delay line and increase the delay by creating a loop in the structure. The proposed method has been experimentally tested and verified for up to 5 roundtrips. The relative delay/advancement was increased up to 5 times compared to the original setup while preserving the original setup's advantages. © VDE VERLAG GMBH
Performance comparison of a novel DFT-based method and conventional channel coding methods for clipping noise cancellation in OFDM systems, Article IEICE Transactions on Communications ; Volume E87-B, Issue 4 , 2004 , Pages 1034-1036 ; 09168516 (ISSN) ; Azmi, P ; Marvasti, F ; Sharif University of Technology
Institute of Electronics, Information and Communication, Engineers, IEICE 2004
A DFT-Based method (DBM) has been proposed to compensate for the performance degradation caused by clipping distortion at the expense of bandwidth expansion. On the other hand, in any communication systems, conventional channel coding methods can be employed to improve performance. In this letter, the performance of the DBM and the channel coding methods (CCM) are compared. Furthermore, we introduce a hybrid system which outperforms both the DBM and the CCM
Article Applied Computational Electromagnetics Society Journal ; Volume 18, Issue 2 , 2003 , Pages 121-127 ; 10544887 (ISSN) ; Sarshar, N ; Barkeshli, K ; Sharif University of Technology
A new method for the robust estimation of target orientation using measured radar cross section is proposed. The method is based on a Generalized Regression Neural Network (GRNN) scheme. The network is trained by the FFT modulus of bistatic radar cross section data sampled at the receiver positions. The target value to be trained is the angle between a defined target orientation and the incident wave. Results based on actual measurements are presented
Article 2007 9th International Symposium on Signal Processing and its Applications, ISSPA 2007, Sharjah, 12 February 2007 through 15 February 2007 ; 2007 ; 1424407796 (ISBN); 9781424407798 (ISBN) ; Manzuri Shalmani, M. T ; Aghatabar, M. M ; Sharif University of Technology
In this paper, we have focused on finding an error resilient method for discontinuity-less transmission of speech signals in the internet. Our proposed method creates artificial correlation between speech samples that pre-distorts the speech signal. The receiver uses this correlation to reconstruct the lost speech packets. A discrete Fourier transform (DFT)-based speech enhancement technique is designed for the reduction of the processing error in the recovered speech caused by the speech codecs. The SegSNR results show the superiority of our proposed method over a recently proposed speech enhancement technique. ©2007 IEEE
Article Optics Letters ; Volume 40, Issue 22 , 2015 , Pages 5239-5242 ; 01469592 (ISSN) ; Arik, K ; Khavasi, A ; Kavehvash, Z ; Sharif University of Technology
OSA - The Optical Society 2015
We introduce the new concept of "metalines" for manipulating the amplitude and phase profile of an incident wave locally and independently. Thanks to the highly confined graphene plasmons, a transmit-array of graphene-based metalines is used to realize analog computing on an ultracompact, integrable, and planar platform. By employing the general concepts of spatial Fourier transformation, a well-designed structure of such meta-transmit-array, combined with graded index (GRIN) lenses, can perform two mathematical operations, i.e., differentiation and integration, with high efficiency. The presented configuration is about 60 times shorter than the recent structure proposed by Silva et al....
Article Optics Letters ; Volume 42, Issue 7 , 2017 , Pages 1197-1200 ; 01469592 (ISSN) ; Chizari, A ; Eshaghian Dorche, A ; Jamali, M. V ; Salehi, J. A ; Sharif University of Technology
OSA - The Optical Society 2017
Leveraging subwavelength resonant nanostructures, plasmonic metasurfaces have recently attracted much attention as a breakthrough concept for engineering optical waves both spatially and spectrally. However, inherent ohmic losses concomitant with low coupling efficiencies pose fundamental impediments over their practical applications. Not only can all-dielectric metasurfaces tackle such substantial drawbacks, but also their CMOS-compatible configurations support both Mie resonances that are invariant to the incident angle. Here, we report on a transmittive metasurface comprising arrayed silicon nanodisks embedded in a homogeneous dielectric medium to manipulate phase and amplitude of...
Article Journal of Optics A: Pure and Applied Optics ; Volume 9, Issue 7 , 2007 , Pages 560-564 ; 14644258 (ISSN) ; Rashidian, B ; Sharif University of Technology
The most important disadvantage of swinging interferometers is that the optical path difference created in them is a nonlinear function of the rotation angle. In this paper, two new swinging interferometers are presented which have good linearity and provide a larger path difference in response to the rotation angle compared to other interferometers. This makes them suitable for applications such as high-resolution spectroscopy, and precision micro and nanopositioning. In one of these two interferometers, the optical path difference is created by rotation of a system composed of four mirrors, and in the other one it is created by rotation of a system consisting of two mirrors. They are not...
Article IEE Proceedings: Communications ; Volume 152, Issue 2 , 2005 , Pages 151-156 ; 13502425 (ISSN) ; Marvasti, F ; Sharif University of Technology
By puncturing the Reed-Solomon codes with the block lengths of 2 m, it is possible to design systematic and nonsystematic codes with arbitrary block lengths and rates that can be decoded using FFT. Because the Reed-Solomon (RS) codes are maximum distance separable (MDS), the resultant codes keep this property as well. The codes are constructed over prime fields as opposed to the conventional practice of extension fields, and hence additions and multiplications are simple mod operations and there is no need to use polynomials and look-up tables. © IEE, 2005
Article 2017 12th International Conference on Sampling Theory and Applications, SampTA 2017, 3 July 2017 through 7 July 2017 ; 2017 , Pages 327-330 ; 9781538615652 (ISBN) ; Marvasti, F ; Anbarjafari, G ; Kivinukk, A ; Tamberg, G ; Sharif University of Technology
This paper proposes some bounds on maximum of magnitude of a random mask in Fourier domain. The random mask is used in random sampling scheme. Having a bound on the maximum value of a random mask in Fourier domain is very useful for some iterative recovery methods that use thresholding operator. In this paper, we propose some different bounds and compare them with the empirical examples. © 2017 IEEE
Article Fourth IEEE International Symposium on Signal processing and Information Technology, ISSPIT 2004, Rome, 18 December 2004 through 21 December 2004 ; 2004 , Pages 314-317 ; 0780386892 (ISBN) ; Jamzad, M ; Sharif University of Technology
The success of restoring images degraded by motion blur highly depends on precise estimation of parameters such as motion direction and length that were involved in the motion blur function. In this paper we suggest a method which uses Radon transform to estimate motion direction and for estimating motion length we used curve fitting methods to provide an equation that could model the behaviour of Fourier transform of images that were degraded with different motion lengths. The input to this model is a property found to be available in the Fourier transform of the degraded image and its output is an estimate for the motion length. Our method was tested on a wide range of different type of...
Article IEEE Antennas and Propagation Society Symposium 2004 Digest held in Conjunction with: USNC/URSI National Radio Science Meeting, Monterey, CA, 20 June 2004 through 25 June 2004 ; Volume 2 , 2004 , Pages 1291-1294 ; 02724693 (ISSN) ; Toghraee, R ; Salimi, K ; Sharif University of Technology
We have constructed the Koch array factor using decomposition of the array factor and solving it with matrix methods, rather than regular inverse Fourier transform method. With the aid of non-uniform sampling we have made some improvements in the main beam while the array elements are reduced significantly. We have also consider the Fibonnaci Sierpinski gasket
Article Electronics Letters ; Volume 39, Issue 23 , 2003 , Pages 1690-1691 ; 00135194 (ISSN) ; Baghai Wadji, A. R ; Sharif University of Technology
A unified and robust method has been introduced to compute magnetostatic and electrostatic fields for nonperiodic excitations in periodically corrugated anisotropic structures. The method extends a previously published concept of modified phased-periodic Green's functions for solving flat-surface problems. Convergent results have been obtained for corrugations with aspect ratios exceeding 15. Novel elemental field distributions are presented as examples
Article Journal of Vibration and Acoustics, Transactions of the ASME ; Volume 135, Issue 5 , 2013 ; 10489002 (ISSN) ; Vafai, A ; Choobbasti, A. J ; Malidarreh, N. R ; Szidarovszky, F ; Sharif University of Technology
An analytical approach has been applied to obtain the solution of Navier's equation for a homogeneous, isotropic half-space under an inertial foundation subjected to a timeharmonic loading. Displacement potentials were used to change the Navier's equation to a system of wave-type equations. Calculus of variation was employed to demonstrate the contribution of the foundation's inertial effects as boundary conditions. Use of the Fourier transformation method for the system of Poisson-type equations and applying the boundary conditions yielded the transformed surface displacement field. Direct contour integration has been employed to achieve the surface waves. In order to clarify the...
Article Asia-Pacific Power and Energy Engineering Conference, APPEEC ; 2011 ; 21574839 (ISSN) ; 9781424462551 (ISBN) ; Ranjbar, A. M ; IEEE Power and Energy Society (PES); Chinese Society for Electrical Engineering (CSEE); State Grid Corporation of China; China Southern Power Grid; Wuhan University ; Sharif University of Technology
This paper presents a new method in order to predict the monthly electricity peak load of a country based on the prediction of Discrete Fourier Transform (DFT) of monthly peak electricity demand variation using the ARIMA methodology. For validation, the result of this method was used to predict monthly peak load variation of the recent two years in Iranian national grid. The primary goal of this article is to show the application and implementation of Discrete Fourier Transform to predict monthly variation of electricity peak load in national electric power systems. Furthermore, it is elaborated to demonstrate the benefits and shortcomings of DFT approach comparing to the commonly used...
Effect of electron irradiation on dye and printability of polypropylene (PP) fabrics: A novel method for decoration of PP fabrics, Article Journal of the Textile Institute ; Volume 101, Issue 11 , Sep , 2010 , Pages 988-995 ; 00405000 (ISSN) ; Shahidi, S ; Ghoranneviss, M ; Wiener, J ; Anvari, A ; Sharif University of Technology
Polypropylene (PP) has a very low value of the surface free energy (approximately 20-25 mJ m-2). And thus, has very weak hydrophilic properties and doesn't have any affinity to any dyestuffs, such as cationic or anionic dyes. In this study, we covered some parts of PP fabrics by mask, and then irradiated them by electrons with different energies. After electron irradiation, the samples were dyed by cationic dyestuff. The result showed that, electron irradiated parts could be dyed easily and the fabric could be printed and decorated simply. The treated surfaces were investigated by scanning electron microscope (SEM), reflective spectrophotometery, and Fourier transform infrared spectroscopy...
An investigation of the surface morphology of nanostructured nickel thin films prepared by electrodeposition, Article International Journal of Surface Science and Engineering ; Volume 10, Issue 5 , 2016 , Pages 444-455 ; 1749785X (ISSN) ; Dolati, A ; Sharif University of Technology
Inderscience Enterprises Ltd
Nickel nanostructure thin films were electrodeposited on copper plates to investigate the fractal study. Scharifker's equations were derived for instantaneous and progressive nucleation and 3D growth of hemispherical centres under diffusion-controlled condition to calculate in situ change of fractal dimension of surface. It was assumed that the layer could be formed completely when fractal dimension of surface inclined to 2. Moreover, the fractal analysis of atomic force microscopy (AFM) images has confirmed the presumed model. Also, the power values of power spectral density (PSD) of the AFM images were determined using fast Fourier transform (FFT) algorithms. The PSD plots are approximated...
Article Optics Letters ; Volume 41, Issue 15 , 2016 , Pages 3451-3454 ; 01469592 (ISSN) ; Abdollahramezani, S ; Jamali, M. V ; Salehi, J. A ; Sharif University of Technology
OSA - The Optical Society
In this Letter, we realize the concept of analog computing using an engineered gradient dielectric meta-reflect-array. The proposed configuration consists of individual subwavelength silicon nanobricks, in combination with a fused silica spacer and silver ground plane, realizing a reflection beam with full phase coverage of 2π degrees, as well as an amplitude range of 0 to 1. Spectrally overlapping electric and magnetic dipole resonances, such high-index dielectric metasurfaces can locally and independently manipulate the amplitude and phase of the incident electromagnetic wave. This practically feasible structure overcomes substantial limitations imposed by plasmonic metasurfaces such as...
Article Polymers for Advanced Technologies ; Volume 30, Issue 8 , 2019 , Pages 1968-1977 ; 10427147 (ISSN) ; Vossoughi, M ; Sharif University of Technology
John Wiley and Sons Ltd 2019
The contribution of electrospun nanofibrous membranes (e.NFMs) in the biosensing platforms opens up a new prospect for the invention of faster and more sensitive analytical devices. In this paper, we utilized e.NFM of polyethersulfone (PES) as a solid substrate for the protein immobilization through two different approaches: physical and covalent. Scanning electron microscopy (SEM) and Fourier-transform-infrared (FTIR) tests were performed to study the effect of plasma treatment on protein immobilization efficacy. Moreover, taking advantage of ELISA technique, the influence of different parameters, namely, nanofibers diameter, membrane thickness, plasma treatment time, an incubation time of...
Article Applied Surface Science ; Volume 254, Issue 20 , 15 August , 2008 , Pages 6441-6445 ; 01694332 (ISSN) ; Vesaghi, M. A ; Sharif University of Technology
Polymeric like carbon (PLC) films are grown by a capacitance coupled RF-PECVD on the grounded electrode at room temperature from liquid gas (40% propane and 60% butane) in two regimes with nitrogen and without nitrogen gas. Films are characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), Fourier transform infrared (FTIR) absorption and Raman spectroscopy. The result of FTIR analyses indicates that more than 90% of hydrogen atoms are bonded to carbon with sp 3 hybridization. The abundance of CH 3 is more than that of CH 2 and this one is more than that of CH for carbon with sp 3 hybridization in these films. The C 1s line of the XPS spectra is deconvoluted to...