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Analysis and design of two-dimensional compound metallic metagratings using an analytical method
, Article Optics Express ; Volume 30, Issue 8 , 2022 , Pages 12440-12455 ; 10944087 (ISSN) ; Khavasi, A ; Sharif University of Technology
Optica Publishing Group (formerly OSA)
2022
Abstract
The recently proposed concept of metagrating enables wavefront manipulation of electromagnetic (EM) waves with unitary efficiency and relatively simple fabrication requirements. Herein, two-dimensional (2D) metagratings composed of a 2D periodic array of rectangular holes in a metallic medium are proposed for diffraction pattern control. We first present an analytical method for diffraction analysis of 2D compound metallic metagrating (a periodic metallic structure with more than one rectangular hole in each period). Closed-form and analytical expressions are presented for the reflection coefficients of diffracted orders for the first time. Next, we verify the proposed method's results...
Analytical method for diffraction analysis and design of perfect-electric-conductor backed graphene ribbon metagratings
, Article Optics Express ; Volume 29, Issue 18 , 2021 , Pages 28935-28952 ; 10944087 (ISSN) ; Khavasi, A ; Rejaei, B ; Sharif University of Technology
The Optical Society
2021
Abstract
Graphene-based gratings and metagratings have attracted great interest in the last few years because they could realize various multi-functional beam manipulation, such as beam splitting, focusing, and anomalous reflection in the terahertz (THz) regime. However, most of graphene-based metagratings are designed through numerical simulations, which are very time-consuming. In this paper, an accurate analytical method is proposed for diffraction analysis of a perfect electric conductor (PEC)-backed array of graphene ribbons. In contrast to previous analytical treatments, the proposed method can predict the electromagnetic performance of graphene ribbons not only in the subwavelength regime, but...
Perfect anomalous reflection using a compound metallic metagrating
, Article Optics Express ; Volume 28, Issue 11 , 2020 , Pages 16439-16452 ; Khavasi, A ; Sharif University of Technology
OSA - The Optical Society
2020
Abstract
Metagrating is a new concept for wavefront manipulation that, unlike phase gradient metasurfaces, does not suffer from low efficiency and also has a less complicated fabrication process. In this paper, a compound metallic grating (a periodic metallic structure with more than one slit in each period) is proposed for anomalous reflection. We propose an analytical method for analyzing the electromagnetic response of this grating. Closed-form and analytical expressions are presented for the reflection coefficients of zeroth diffracted order and also higher diffracted orders. The proposed method is verified against full-wave simulations and the results are in excellent agreement. Thanks to the...
Exploiting the ewald method for calculating the t-matrix of arbitrary periodic arrays
, Article 5th International Conference on Millimeter-Wave and Terahertz Technologies, MMWaTT 2018, 18 December 2018 through 20 December 2018 ; Volume 2018-December , 2019 , Pages 62-65 ; 21570965 (ISSN); 9781538677179 (ISBN) ; Rashidian, B ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2019
Abstract
In this study a 3D robust, systematic, semi-analytical method to characterize electromagnetic scattering from periodic arrays of discrete scatterers is presented. The proposed method is based on the multiple-scattering T-matrix in connection with the Ewald method. The formulation is systematic, quite general, easily traceable, and fast. Its high speed of analysis makes it well suited to design optimizations. The formulation is well developed for obliquely incident plane waves, and can be extended to Gaussian beams by means of suitable plane wave decomposition. For validating the proposed method, an example of a scattering problem is solved, and the resulting scattering spectrum, and the...
Effect of graphene on the absorption and extraordinary transmission of light in 1-d metallic gratings
, Article IEEE Journal of Quantum Electronics ; Volume 53, Issue 3 , 2017 ; 00189197 (ISSN) ; Rahmani, B ; Khavasi, A ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2017
Abstract
Periodic metallic structures are known to support resonant extraordinary optical transmission (EOT). When covered with graphene, these structures can be employed to effectively manipulate the light. In this paper, we propose an analytical circuit model for graphene-covered 1-D metallic gratings. By using the circuit theory, we demonstrate that 1-D periodic array of cut-through slits, which are covered by a continuous graphene sheet, exhibits tunable EOT resonance for TM polarization whose amplitude, unlike its spectral position, can be dynamically tuned by varying the Fermi level of graphene. In this fashion, it is shown that placing a perfect reflector at the bottom of the graphene-covered...
In-plane and out-of-plane waves in nanoplates immersed in bidirectional magnetic fields
, Article Structural Engineering and Mechanics ; Volume 61, Issue 1 , 2017 , Pages 65-76 ; 12254568 (ISSN) ; Gharebaghi, S. A ; Mehri, B ; Sharif University of Technology
Techno Press
2017
Abstract
Prediction of the characteristics of both in-plane and out-of-plane elastic waves within conducting nanoplates in the presence of bidirectionally in-plane magnetic fields is of interest. Using Lorentz's formulas and nonlocal continuum theory of Eringen, the nonlocal elastic version of the equations of motion is obtained. The frequencies as well as the corresponding phase and group velocities pertinent to the in-plane and out-of-plane waves are analytically evaluated. The roles of the strength of in-plane magnetic field, wavenumber, wave direction, nanoplate's thickness, and small-scale parameter on characteristics of waves are discussed. The obtained results show that the in-plane...
Exposure of the human brain to an electromagnetic plane wave in the 100-1000 MHz frequency range for potential treatment of neurodegenerative diseases
, Article IET Microwaves, Antennas and Propagation ; Volume 6, Issue 14 , 2012 , Pages 1565-1572 ; 17518725 (ISSN) ; Eslampanah Sendi, M.S ; Chávez Santiago, R ; Mesiti, F ; Balasingham, I ; Sharif University of Technology
2012
Abstract
Radio signals can induce an electric field inside the brain, which might be potentially beneficial in the treatment of neurodegenerative diseases. For instance, a new method for the treatment of Alzheimer's disease in mice through the exposure to the radiation of mobile phones has been successfully demonstrated. In the light of these results, studying the induction of an electric field in the human brain through the controlled exposure to radio signals is of paramount importance for the eventual development of similar treatment techniques in humans. In this study, the authors study the radio signals in 100-1000 MHz as a means for inducing an electric field into the human brain in a...
Determination of complex modes in photonic crystal waveguides using the phase variation in characteristic coefficients
, Article Optics Letters ; Volume 37, Issue 15 , 2012 , Pages 3078-3080 ; 01469592 (ISSN) ; Khavasi, A ; Sarrafi, P ; Mehrany, K ; Sharif University of Technology
OSA Pub
2012
Abstract
An efficient frequency-domain method, the phase variation monitoring (PVM) method, is proposed to determine the electromagnetic eigenmodes in two-dimensional photonic crystal waveguides. The proposed method is based on monitoring the reflection and transmission coefficients of incident plane waves. It is successfully applied to an illustrative line-defect photonic crystal waveguide and proved to be capable of calculating the in-plane leakage through the finite-size photonic crystal surrounding the line-defect. Calculation of the leakage loss is not only important for proper understanding of wave propagation within the defect but also for its significant role in applications of photonic...
First principles study of oxygen adsorption on nickel-doped graphite
, Article Molecular Physics ; Volume 110, Issue 13 , Feb , 2012 , Pages 1437-1445 ; 00268976 (ISSN) ; Gobal, F ; Sharif University of Technology
2012
Abstract
Density functional theory is used in a spin-polarized plane wave pseudopotential implementation to investigate molecular oxygen adsorption and dissociation on graphite and nickel-doped graphite surfaces. Molecular oxygen physisorbs on graphite surface retaining its magnetic property. The calculated adsorption energy is consistent with the experimental value of 0.1eV. It is found that substituting a carbon atom of the graphite surface by a single doping nickel atom (2.8% content) makes the surface active for oxygen chemisorption. It is found that the molecular oxygen never adsorbs on doping nickel atom while it adsorbs and dissociates spontaneously into atomic oxygens on the carbon atoms...
Approximate expressions for resonant shifts in the reflection of Gaussian wave packets from two-dimensional photonic crystal waveguides
, Article Journal of the Optical Society of America B: Optical Physics ; Volume 29, Issue 4 , 2012 , Pages 683-690 ; 07403224 (ISSN) ; Khavasi, A ; Alishahi, F ; Mehrany, K ; Rashidian, B ; Sharif University of Technology
Optical Society of American (OSA)
2012
Abstract
In this paper, enhanced spatial and temporal shifts in the reflection of Gaussian wave packets from twodimensional photonic crystal waveguides supporting above-the-light-line leaky modes are studied, for the first time to our best knowledge. Particular attention is given to two important special cases, namely, harmonic Gaussian beams and Gaussian-pulse uniform plane waves. Analytical expressions are given for enhanced spatial and temporal shifts when the stationary phase approximation holds and the incident wave excites above-the-light-line leaky modes. The enhanced spatial and temporal shifts of Gaussian wave packets are thereby related to each other via the group velocity of the excited...
A novel method for band structure analysis of photonic crystal slabs
, Article IEEE Photonics Journal ; Volume 3, Issue 6 , 2011 , Pages 1111-1122 ; 19430655 (ISSN) ; Akbari, M ; Mehrany, K ; Sharif University of Technology
2011
Abstract
We propose a new method to extract the modes of photonic crystal slabs and, thus, obtain their band structures. These slabs, which are 2-D periodic structures with finite thickness, can completely confine light and have the important advantage of simple construction for applications in integrated optic devices. In this paper, reflection pole method (RPM) is utilized to analyze photonic crystal slabs. Modes are poles of reflection and transmission coefficients of multilayered structures. According to this principle, modes can be detected by only pursuing phase variations of transmission coefficients that are equal to π rad. Therefore, extraction of modes becomes fast and simple through...
Electron correlation in Sr(Ca)RuO 3 by GWA and LSDA+U
, Article European Physical Journal B ; Volume 84, Issue 2 , November , 2011 , Pages 203-217 ; 14346028 (ISSN) ; Akhavan, M ; Sharif University of Technology
2011
Abstract
We have investigated the role of electron-electron correlation in SrRuO 3 and CaRuO 3 bulk structures. At first, the DOS of SrRuO 3 and CaRuO 3 is obtained using the full potential linearized augmented plane wave method by LSDA. We have then calculated the electronic structure, dielectric function, self-energy, and spectral function for the bulk SrRuO 3 and CaRuO 3 by GWA. The shifting of the Ru t 2g orbitals, broadening in Ru valance bands, and also the enhancement in exchange splitting shows better agreement between the GWA many-body correction with the bulk experimental results. But, in spite of the many-body correction, the GWA results is not completely consistent with the PES...
Analyzing symmetry in photonic band structure of gyro-magnetic photonic crystals
, Article Proceedings of SPIE - The International Society for Optical Engineering ; Volume 8096 , 2011 ; 0277786X (ISSN) ; 9780819487063 (ISBN) ; Khorasani, S ; Gholami, F ; Sharif University of Technology
2011
Abstract
In the band structure analysis of photonic crystals it is normally assumed that the full photonic gaps could be found by scanning high-symmetry paths along the edges of Irreducible Brillouin Zones (IBZ). We have recently shown [1] that this assumption is wrong in general for sufficiently symmetry breaking geometries, so that the IBZ is exactly half of the complete BZ. That minimal required symmetry arises from the requirement on time-reversal symmetry. In this paper we show that even that requirement might be broken by using gyro-magnetic materials in the composition of photonic structures we can observe that the IBZ extends fully to the boundaries of the complete BZ, that is IBZ must be as...
Effect of electron correlation in Sr(Ca)Ru1-xCrxO3: Density functional calculation
, Article Journal of Solid State Chemistry ; Volume 183, Issue 7 , 2010 , Pages 1678-1690 ; 00224596 (ISSN) ; Akhavan, M ; Sharif University of Technology
2010
Abstract
We have investigated the electronic structure of Sr(Ca)Ru1-xCrxO3 using the full potential linearized augmented plane wave method by different approximation such as LSDA and LSDA+U. The LSDA calculation suggest that Cr4+-Ru4+ hybridization is responsible for the high Curie temperature TC in SrRu1-xCrxO3, but it cannot completely describe its physical behavior. Our LSDA+U DOS results for SrRu1-xCrxO3 clearly establishes renormalization of the intra-atomic exchange strength at the Ru sites, arising from the Cr-Ru hybridization. The antiferromagnetic coupling of Cr3+ with Ru4+,5+ lattice increases the screening, which is consistent with the low magnetic moment of the Ru ions. The more distorted...
Formulation of differential transfer matrix method in cylindrical geometry
, Article Proceedings of SPIE - The International Society for Optical Engineering, 25 January 2010 through 28 January 2010 ; Volume 7597 , January , 2010 ; 0277786X (ISSN) ; 9780819479938 (ISBN) ; Khorasani, S ; Rashidian, B ; Mohammadi, S ; Sharif University of Technology
2010
Abstract
Transfer and scattering matrix methods are widely in use for description of the propagation of waves in multilayered media. When the profile of refractive index is continuous, however, a modified formulation of transfer matrices does exist, which provides a complete analytical solution of the wave phenomena in such structures. Previously reported variations of the so-called Differential Transfer Matrix Method (DTMM) had been limited to Cartesian geometry where layered media form one-dimensional structures and plane waves are used as basis functions. In this work, we extend the formalism to cylindrical geometry with radial symmetry, in which Bessel functions need to be employed as basis...
Influence of asymmetry on the band structure of photonic crystals
, Article Proceedings of SPIE - The International Society for Optical Engineering, 26 January 2010 through 28 January 2010 ; Volume 7609 , January , 2010 ; 0277786X (ISSN) ; 9780819480057 (ISBN) ; Khorasani, S ; Sharif University of Technology
2010
Abstract
Computer calculation of photonic band structure for unit cells of various symmetry in the two-dimensional square lattice suggests that the bandgap calculated by traversing the ΓXM triangle in k-space is only reliable when the unit cell is C4v symmetric. For structures of lower symmetry, examining a two-dimensional subset of the first Brillouin zone will give smaller bandgaps
How T c can go above 100 K in the YBCO family
, Article European Physical Journal B ; Volume 73, Issue 1 , 2010 , Pages 79-83 ; 14346028 (ISSN) ; Akhavan, M ; Sharif University of Technology
2010
Abstract
We report the results of the electronic structure calculation of a newly discovered member of the YBCO high-T c family, i.e., Y 3Ba 5Cu 8O 18 (Y358) with T c>100, based on the full-potential linearized augmented plane waves method (FP-LAPW) of density functional theory in the generalized gradient approximation (GGA). The evolution of the number of hole carriers in different sites of the CuO 2 planes and CuO chains has been investigated in comparison with the other YBCO family members, i.e., Y123, Pr123, Y124, and Y247. The results suggest that pumping hole carriers out of the chains toward the planes enhances the transition temperature. The band structure calculations have been performed for...
Revised guided mode expansion on dispersive photonic media
, Article Photonic and Phononic Crystal Materials and Devices IX, San Jose, CA, 27 January 2009 through 29 January 2009 ; Volume 7223 , 2009 ; 0277786X (ISSN) ; Sodagar, M ; Khoshnegar, M ; Khorasani, S ; Chamanzar, M. R ; Adibi, A ; Sharif University of Technology
2009
Abstract
A novel plane-wave-based approach for analytical treatment of dispersive relation is developed and applied to analyze the behavior of electromagnetic waves in plasmonic-photonic-crystal slabs. Here Drude model is used for describing frequency dependent permittivity of plasma rods in host dielectric medium. In the present work, dispersion relation below and above the light line is calculated approximately by means of Maxwell-Garnett effective medium and Revised Plane Wave Method (RPWM). The eigen-functions are then used in Revised Guided Mode Expansion (RGME) as the set of orthonormal bases. Following this procedure, the accurate band structure is obtained. In these kind of methods there are...
Ag Raman modes of RBCO (R = Gd, Pr) by density functional theory approach
, Article European Physical Journal B ; Volume 51, Issue 2 , 2006 , Pages 161-165 ; 14346028 (ISSN) ; Tavana, A ; Akhavan, M ; Sharif University of Technology
2006
Abstract
Ab initio total energy calculations have been performed for superconducting GdBa2Cu3O7 and insulating PrBa 2Cu3O7 using the full-potential linear augmented plane-wave method in the local density approximation (LDA) and generalized gradient approximation (GGA). The comparison of the calculated unit cell volume and lattice parameters with the experimental data indicates the improvement of these parameters in the GGA relative to LDA. LDA and GGA give the equilibrium unit cell volume about 6% smaller and 1.25% larger than the experimental data, respectively for both systems. Thus frozen phonon calculations have been performed to determine the eigenvalues and eigenvectors of the k=0 Ag modes of...
Modal transmission-line theory of optical waveguides
, Article Journal of Electromagnetic Waves and Applications ; Volume 19, Issue 7 , 2005 , Pages 891-906 ; 09205071 (ISSN) ; Akbari, M ; Sharif University of Technology
2005
Abstract
In this paper, we describe a vectorial and analytical technique, based on modal transmission-line theory, for solving guided modes of arbitrary shaped cylindrical optical waveguides. The waveguide materials can be either transparent or absorbing. In this technique, mode solving is approached by periodic repetition of the waveguide and using modal transmission-line theory. Pertinent information about guided modes of the waveguide is extracted from transmission-line features. Two examples illustrate the utilization of this technique for analysis of optical waveguides