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    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) Najafi, A ; Khorasani, S ; Gholami, F ; Sharif University of Technology
    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... 

    Efficient analysis of confined guided modes in phoxonic crystal slabs

    , Article Journal of Lightwave Technology ; Volume 35, Issue 17 , 2017 , Pages 3734-3742 ; 07338724 (ISSN) Aram, M. H ; Khorasani, S ; Sharif University of Technology
    Today's standard fabrication processes are just capable of manufacturing slab of photonic and phononic crystals, so an efficient method for analysis of these crystals is indispensable. Plane wave expansion (PWE) as a widely used method in studying photonic and phononic (phoxonic) crystals in full three dimensions is not suitable for slab analysis in its standard form, because of convergence and stability issues. Here, we propose a modification to this method which overcomes these limitations. This improved method can be utilized for calculation of both photonic and phononic modes in phoxonic slabs. While in the standard three-dimensional PWE, Fourier series are used to estimate the field... 

    Construction of Dirac points using triangular supercrystals

    , Article Applied Physics A: Materials Science and Processing ; Volume 115, Issue 2 , May , 2014 , Pages 581-587 ; ISSN: 09478396 Aram, M. H ; Mohajeri, R ; Khorasani, S ; Sharif University of Technology
    We show a methodology for how to construct Dirac points that occur at the corners of Brillouin zone as the Photonic counterparts of graphene. We use a triangular lattice with circular holes on a silicon substrate to create a Coupled Photonic Crystal Resonator Array (CPCRA) which its cavity resonators play the role of carbon atoms in graphene. At first we draw the band structure of our CPCRA using the tight-binding method. For this purpose we first designed a cavity which its resonant frequency is approximately at the middle of the first H-polarization band gap of the basis triangular lattice. Then we obtained dipole modes and magnetic field distribution of this cavity using the Finite... 

    Perfect anomalous reflection using a compound metallic metagrating

    , Article Optics Express ; Volume 28, Issue 11 , 2020 , Pages 16439-16452 Rahmanzadeh, M ; Khavasi, A ; Sharif University of Technology
    OSA - The Optical Society  2020
    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... 

    The Scattering of Electro-Elastic Fields of an SH-Wave in a
    Piezoelectric Medium by an Eccentric Two-Phase Circular
    Piezoelectric Micro Sensor

    , M.Sc. Thesis Sharif University of Technology Jarfi, Hamid (Author) ; Mohammadi Shodja, Hossein (Supervisor)
    This thesis presents an analytical solution for determination of the
    electro-elastic media subjected to an anti plane shear harmonic wave containing a multi-phase cylindrical fiber whose electro-elastic properties differ from those of the matrix. Both the matrix and the coated-fiber system are transversely isotropic piezoelectric materials with symmetry and poling axes parallel to the fiber axis. The coating can have variable thickness. The dynamic electro-mechanical equivalent inclusion method (DEMEIM) is presented and employed as an extension of dynamic equivalent inclusion method (DEIM) in order to take into account the electro-mechanical coupling. Accordingly, the coating-fiber... 

    Investigation of a quasi-3D plasmonic nanostructure for TE and TM polarizations

    , Article Journal of the Optical Society of America B: Optical Physics ; Vol. 31, issue. 11 , 2014 , p. 2838-2844 Shahmansouri, A ; Rashidian, B ; Sharif University of Technology
    Quasi-3D plasmonic nanostructures consisting of a metallic film perforated as an array of nanoholes, separated by a gap from a nanodisk array, are theoretically investigated under plane wave illumination with transverse electric and transverse magnetic polarizations. The results are compared with the results of a simple nanodisk array. A full discussion involving the couplings between plasmon resonance in nanodisks, surface plasmon polaritons on the interfaces of metallic film, and different diffractive grating orders that contribute in the couplings will be presented. The large difference between the plasmon behavior of the nanodisk array alone and nanodisk array in the presence of nanohole... 

    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) Khaleghi, A ; Eslampanah Sendi, M.S ; Chávez Santiago, R ; Mesiti, F ; Balasingham, I ; Sharif University of Technology
    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) Hosseinnia, A. H ; Khavasi, A ; Sarrafi, P ; Mehrany, K ; Sharif University of Technology
    OSA Pub  2012
    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... 

    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) Miri, M ; Khavasi, A ; Alishahi, F ; Mehrany, K ; Rashidian, B ; Sharif University of Technology
    Optical Society of American (OSA)  2012
    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... 

    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) Bagheri, A ; Rahmani, B ; Khavasi, A ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2017
    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... 

    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) Armand, M. J ; Rashidian, B ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2019
    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... 

    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) Khosroabadi, H ; Tavana, A ; Akhavan, M ; Sharif University of Technology
    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... 

    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) Rahmanzadeh, M ; Khavasi, A ; Rejaei, B ; Sharif University of Technology
    The Optical Society  2021
    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... 

    Modal transmission-line theory of optical waveguides

    , Article Journal of Electromagnetic Waves and Applications ; Volume 19, Issue 7 , 2005 , Pages 891-906 ; 09205071 (ISSN) Dabirian, A ; Akbari, M ; Sharif University of Technology
    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  

    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) Eftekharian, A ; Sodagar, M ; Khoshnegar, M ; Khorasani, S ; Chamanzar, M. R ; Adibi, A ; Sharif University of Technology
    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... 

    Improving the Quality and Speed Ultrasonic Image Reconstruction Using the K_SVD Algorithm

    , M.Sc. Thesis Sharif University of Technology Alimoradi, Zahra (Author) ; Jahed, Mehran (Supervisor) ; Kaveh Vash, Zahra (Co-Supervisor)
    Ultrasound imaging is one of the most widely used diagnostic methods in medicine due to its safety, cost-effectiveness and small and portable size of equipment. In this imaging method, line-by-line scanning is used to create the image, which has limitations in speed and resolution. To deal with these limitations, new methods have been proposed, such as plane-wave imaging with the possibility of increasing the imaging speed and synthetic apertures with the possibility of increasing the quality of images. By combining these two methods, high quality and speed can be achieved simultaneously. Therefore, in this research, based on previous studies, a number of elements were activated each time,... 

    First principles study of oxygen adsorption on nickel-doped graphite

    , Article Molecular Physics ; Volume 110, Issue 13 , Feb , 2012 , Pages 1437-1445 ; 00268976 (ISSN) Nahali, M ; Gobal, F ; Sharif University of Technology
    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... 

    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) Nekuee, S. A. H ; Akbari, M ; Mehrany, K ; Sharif University of Technology
    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) Hadipour, H ; Akhavan, M ; Sharif University of Technology
    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... 

    Ferromagnetism and antiferromagnetism coexistence in SrRu 1-xMnxO3: Density functional calculation

    , Article Journal of Solid State Chemistry ; Volume 184, Issue 3 , March , 2011 , Pages 536-545 ; 00224596 (ISSN) Hadipour, H ; Fallahi, S ; Akhavan, M ; Sharif University of Technology
    We have calculated the electronic structure of SrRu1-xMn xO3 using the full potential linearized augmented plane wave method by LSDA and LSDAU. The antiparallel alignment between the Mn and Ru ions are consistent with the competition between ferromagnetism and antiferromagnetism in the low Mn-doped polycrystalline samples. This is in contrast to the appearance of quantum critical point and FM and AFM transitions in the single crystal measurement. Our results show that the discrepancy between different experimental phase diagrams is related to the conditions of sample preparation and also the difference between the degree of magnetic interactions between the Mn and Ru moments. The DOS and the...