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absorbances
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Polarization insensitive, wide angle and wideband anisotropic metamaterial absorber comprising phase change Ge2Sb2Te5 (GST)/SiO2 layered media
, Article Waves in Random and Complex Media ; 2022 ; 17455030 (ISSN) ; Abdulrazak, L. F ; Akhtar, M. N ; Sharif University of Technology
Taylor and Francis Ltd
2022
Abstract
Perfect metamaterial absorbers (PMAs) are crucial for sensing, energy harvesting, cloaking, and solar cell, as these can perfectly absorb electromagnetic waves in the broad range of electromagnetic spectra. Due to these remarkable applications, PMAs have extensively attracted the attention of numerous researchers. However, to date, narrow- and wide-band absorbers have been investigated, recently wideband absorption is the primary concern of electromagnetic communities. In this paper, absorption features of the metasurface-based absorber are analyzed. The PMA is made of three layers–a top metasurface fabricated over silicon dioxide (SiO2) with a backside coated with a thin layer of silver...
Polarization insensitive and broadband terahertz absorber using graphene disks
, Article Plasmonics ; Volume 12, Issue 2 , 2017 , Pages 393-398 ; 15571955 (ISSN) ; AbdollahRamezani, S ; Khavasi, A ; Sharif University of Technology
Springer New York LLC
2017
Abstract
We demonstrate design and characterization of a polarization-independent ultra-broadband absorber of light consisting of periodic array of graphene disks on top of a lossless quarter-wavelength dielectric spacer placed on a metallic reflector. The absorber is duly designed based on impedance matching concept by proposing a fully analytical circuit model resulting in a normalized bandwidth of 100 % in the terahertz regime. © 2016, Springer Science+Business Media New York
Optimization of synthetic conditions CMC-g-poly (acrylic acid)/celite composite superabsorbent by taguchi method and determination of its absorbency under load
, Article Express Polymer Letters ; Volume 1, Issue 8 , 2007 , Pages 488-494 ; 1788618X (ISSN) ; Amini Fazl, M. S ; Ayyari, M ; Sharif University of Technology
2007
Abstract
A novel biopolymer-based composite hydrogel was synthesized through chemical crosslinking by graft copolymerization of partially neutralized acrylic acid onto the carboxymethyl cellulose (CMC). The Taguchi method, a robust experimental design, was employed for the optimization of the synthesis based on the swelling capacity of the hydrogels. This method was applied for the experiments and standard L16 orthogonal array with five factors and four levels. In the synthesis of the composite superabsorbent, N,N'-methylene bisacrylamide (MBA) as crosslinker, ammonium persulfate (APS) as initiator, acrylic acid (AA) as monomer, CMC/Celite weight ratio and neutralization percent (NU) were used as...
Adaptive-passive structural vibration attenuation using distributed absorbers
, Article Proceedings of the Institution of Mechanical Engineers, Part K: Journal of Multi-body Dynamics ; Volume 216, Issue 3 , 2002 , Pages 223-235 ; 14644193 (ISSN) ; Esmailzadeh, E ; Sharif University of Technology
Professional Engineering Publishing
2002
Abstract
A distributed dynamic vibration absorber with adaptive capability is presented to improve vibration suppression characteristics of harmonically excited structures. A double-ended cantilever beam carrying intermediate lumped masses forms the absorber subsection. The adaptive capability is achieved through concurrent adjustment of the positions of the moving masses, along the beam, to comply with the desired optimal performance. The necessary and sufficient conditions for the existence of periodic oscillatory behaviour, along with some physical bounds placed on the absorber parameters, form a constrained optimization problem for the optimum tuning strategy. Through numerical simulations it is...
Design, Simulation and Fabrication of Thz Absorber for Thermal Superconducting Detector
, M.Sc. Thesis Sharif University of Technology ; Fardmanesh, Mehdi (Supervisor)
Abstract
At almost all frequencies, we have good methods to generate and detect electromagnetic radiations. One crucial exception is the low terahertz range,where despite intensive research there is a severe lack of proper devices for many applications in this frequency range such as oscillators and detectors that is so-called THz gap and includes 0.3 to 10 THz spectrum. There are different types of THz detectors but bandwidth of dection of most of them is narrow. Among these detectors, superconducting transition edge balometer detector has detectivity in wide frequency range. But generally, detectivity of these detectors strongly depends on their ability to absorb radiations of electromagnetic waves...
Adaptive group of ink drop spread: A computer code to unfold neutron noise sources in reactor cores
, Article Nuclear Engineering and Technology ; 2017 ; 17385733 (ISSN) ; Esmaili PaeenAfrakoti, I ; Sharif University of Technology
Korean Nuclear Society
2017
Abstract
The present paper reports the development of a computational code based on the Adaptive Group of Ink Drop Spread (AGIDS) for reconstruction of the neutron noise sources in reactor cores. AGIDS algorithm was developed as a fuzzy inference system based on the active learning method. The main idea of the active learning method is to break a multiple input-single output system into a single input-single output system. This leads to the ability to simulate a large system with high accuracy. In the present study, vibrating absorber-type neutron noise source in an International Atomic Energy Agency-two dimensional reactor core is considered in neutron noise calculation. The neutron noise...
Tunable extraordinary transmission through a graphene-covered hole array: an analytical equivalent-circuit modeling approach
, Article Plasmonics ; 2018 ; 15571955 (ISSN) ; Khavasi, A ; Sharif University of Technology
Springer New York LLC
2018
Abstract
We study two-dimensional (2D) hole arrays drilled into a perfect conductor slab covered with a graphene sheet. Such arrays support the extraordinary transmission of electromagnetic waves and allow tunability via graphene properties. We investigate the effect of graphene on transmission spectra by proposing an accurate analytical circuit model for the structure, where the graphene contributes an admittance component at the interface. The model demonstrates how extraordinary transmission can be tuned via the graphene conductivity. We study the free-standing structure, where the hole array is covered by a graphene sheet on both sides of the conductor slab, and a substrate-bound hole array...
Tunable extraordinary transmission through a graphene-covered hole array: an analytical equivalent-circuit modeling approach
, Article Plasmonics ; Volume 14, Issue 3 , 2019 , Pages 569-577 ; 15571955 (ISSN) ; Khavasi, A ; Sharif University of Technology
Springer New York LLC
2019
Abstract
We study two-dimensional (2D) hole arrays drilled into a perfect conductor slab covered with a graphene sheet. Such arrays support the extraordinary transmission of electromagnetic waves and allow tunability via graphene properties. We investigate the effect of graphene on transmission spectra by proposing an accurate analytical circuit model for the structure, where the graphene contributes an admittance component at the interface. The model demonstrates how extraordinary transmission can be tuned via the graphene conductivity. We study the free-standing structure, where the hole array is covered by a graphene sheet on both sides of the conductor slab, and a substrate-bound hole array...
Graphene nanopores in broadband wide-angle optical cavity resonance absorbers
, Article Surfaces and Interfaces ; Volume 30 , 2022 ; 24680230 (ISSN) ; Akhavan, O ; Sharif University of Technology
Elsevier B.V
2022
Abstract
A cavity resonator containing graphene nanopores (GNPs), along with a metallic layer (Ag, as a reflector) and a dielectric layer (SiO2, as a spacer), has been proposed for broadband wide-angle absorption of light. The GNP/SiO2/Ag multilayers showed high significant increase in the absorption efficiency (with respect to the G/SiO2/Ag multilayer) in a broad spectral range (from ultra-violet (UV) and visible range to near-infrared (NIR)), due to the cavity resonance and absorptions induced by the oxygen-containing functional groups formed around the nanopores of graphene. The dependences of the cavity resonance absorption on the quality of the GNP layer, dimension of the cavity and the incident...
Fabrication and Characterization of the Buffer Layer and Interface with Absorbent Layer in Chalcopyrite Solar Cells Thin Layers by Solubility-Based Methods
, M.Sc. Thesis Sharif University of Technology ; Taghavinia, Nima (Supervisor) ; Dehghani, Mehdi (Supervisor)
Abstract
In this research, the first attempt was made to increase the thickness of the absorbent layer and increase the size of the absorbent layer crystals and minimize the cavities of this layer. this attempt resulted in the synthesis of absorbent layer with a thickness of about one micrometer and with low cavities. then, an attempt was made to crystallize the buffer layer and form the bond with the absorbent layer. these efforts led to the synthesis of a cadmium sulfide layer with a high carrier density. in this study, cadmium sulfide and cadmium zinc sulfide and indium sulfide were used to make the cell. then we could synthesizing window layer with low resistance.at end, we made superstrate...
Design of mid-infrared ultra-wideband metallic absorber based on circuit theory
, Article Optics Communications ; Volume 381 , 2016 , Pages 309-313 ; 00304018 (ISSN) ; Abdollahramezani, S ; Farajollahi, S ; Khavasi, A ; Rejaei, B ; Sharif University of Technology
Elsevier B.V
2016
Abstract
An ultra-broadband absorber of light is proposed by using periodic array of ultra-thin metallic ribbons on top of a lossless quarter-wavelength dielectric spacer placed on a metallic reflector. We propose a fully analytical circuit model for the structure, and then the absorber is duly designed based on the impedance matching concept. As a result, normalized bandwidth of 99.5% is realized by the proposed absorbing structure in mid-infrared regime. Performing a numerical optimization algorithm, we could also reach to normalized bandwidth of 103%
A novel omega shaped microwave absorber with wideband negative refractive index for C-band applications
, Article Optik ; Volume 242 , 2021 ; 00304026 (ISSN) ; Baqir, M. A ; Iftikhar, A ; Ali, M. M ; Rahim, A. A ; Niaz Akhtar, M ; Mughal, M. J ; Naqvi, S. A ; Sharif University of Technology
Elsevier GmbH
2021
Abstract
This paper reports a polarization controllable and angle-insensitive perfect metamaterial absorber (PMA). The proposed PMA consists of periodically arranged asymmetric omega-shaped resonators made of metallic copper. The absorptivity was analyzed considering the microwave C-band from 4 GHz to 8 GHz. The proposed PMA shows an absorption peak with almost 100% absorptivity at 6.2 GHz. Also, wideband negative index of refraction is observed. Further, the absorber is inspected for the different rotation angles of the top metasurface (omega-shaped ring) along the optical axis, and obliquity of incidence angle for both TE and TM polarized waves. Moreover, surface electric field and surface current...
Microwave absorption characteristic of a double-layer X-band absorber based on MWCNTs/La0.6Sr0.4Mn0.5Fe0.5O4 coated with PEDOT polymer
, Article Ceramics International ; Volume 47, Issue 12 , 2021 , Pages 17736-17744 ; 02728842 (ISSN) ; Dang, X ; Boudaghi, R ; Akhtar, M. N ; Sharif University of Technology
Elsevier Ltd
2021
Abstract
In this study, a novel double-layer microwave absorber was designed based on the MWCNTs/La0.6Sr0.4Mn0.5Fe0.5O4 (C/LSMFO) and PEDOT-coated (P@[C/LSMFO]) nanocomposites. Co-precipitation and in-situ polymerization methods were utilized to synthesize the C/LSMFO and P@[C/LSMFO] nanocomposites, respectively. XRD, FESEM, VSM, and VNA analysis were used to determine the structural, morphological, magnetic, and electromagnetic properties of the nanocomposites. Single-layer absorbers with thicknesses of 1, 1.5, and 2 mm were fabricated, and electromagnetic parameters were evaluated via VNA in the X-band frequency. Moreover, the microwave absorbing features of the double-layer absorber with various...
Enhanced structural, electromagnetic and absorption features of CoSm ferrite-metamaterial absorbers through synergistic effects
, Article Ceramics International ; Volume 48, Issue 20 , 2022 , Pages 29561-29571 ; 02728842 (ISSN) ; Makhdoom, S ; Baqir, M. A ; Yousaf, M ; Khan, M. A ; Batoo, K. M ; Hussain, S ; Sharif University of Technology
Elsevier Ltd
2022
Abstract
Currently, materials with outstanding absorption abilities, such as thin size, better absorbing power, and light weight are the need of industry to resolve the electromagnetic issues. However, the research on optimizing the composition of the material, microstructure and the structure of the absorber are also the important factors for enhancing the absorption features. A metamaterial microwave absorber (MMA) based on nano ferrites with desirable absorption peaks is proposed and simulated. Sol-gel auto combustion route is used to prepare the nanosized Sm doped Co ferrite with Co1+xSmxFe2-2xO4 at x = 0.00, 0.03, 0.06, 0.09, respectively. XRD, VSM, FESEM, and VNA were employed to evaluate the...
Evaluation of a robust dynamic vibration absorber based on negative stiffness and internal resonance against seismic excitation
, Article International Journal of Non-Linear Mechanics ; Volume 146 , 2022 ; 00207462 (ISSN) ; Attari, N. K. A ; Rofooei, F. R ; Sharif University of Technology
Elsevier Ltd
2022
Abstract
In this study, a nonlinear absorber that works with a negative stiffness is introduced to control vibration and its effect on reducing earthquake damage is investigated. Negative stiffness increases structural softness and damping. Also, due to its inherent nonlinear nature, negative stiffness can cause internal resonance and transfer vibration energy from a directly excited vibrating mode to a higher frequency mode. Using these features can be effective in reducing vibration. First, to investigate the dynamic behavior in conditions without internal resonance and with 1:3 internal resonance, the proposed absorber is added to a nonlinear main system and when the system is under external...
Design and Simulation of Electromagnetic Wave Broadband Absorbers Using Metallic and Graphene-based Structures Based on Circuit Theory
, M.Sc. Thesis Sharif University of Technology ; Khavasi, Amin (Supervisor) ; Rejaei, Behzad (Co-Advisor)
Abstract
In this dissertation, we design and simulate Electromagnetic (EM) wave absorbers using periodic array of ultra-thin metallic ribbons, metallic disks and graphene disks based on circuit theory. The equivalent circuit for EM structures significantly eliminates the requirement of systems with advanced hardwares. Firstly, we categorize the metallic absorbers in the literature in two types: narrowband absorbers and broadband absorbers. Surface plasmon polariton, magnetic resonance, interference theory and localized surface plasmon are employed to illustrate the mechanism behind the narrowband absorption. Therefore, they will be the basis for classifying the narrowband absorbers in this work....
Vibration absorber design to suppress regenerative chatter in nonlinear milling process: Application for machining of cantilever plates
, Article Applied Mathematical Modelling ; Volume 39, Issue 2 , 2015 , Pages 600-620 ; 0307904X (ISSN) ; Vossoughi, G ; Behzad, M ; Movahhedy, M. R ; Sharif University of Technology
Elsevier Inc
2015
Abstract
In this paper, a tunable vibration absorber (TVA) is designed to suppress regenerative chatter in milling of cantilever plates. In machining industry, the majority of work-piece materials or the interaction of work-piece/cutting tool causes the cutting forces to demonstrate nonlinear behavior. The application of TVA (as a semi-active controller) is investigated for the process with an extensive nonlinear model of cutting forces. Under regenerative chatter conditions, optimum values of the absorber position and its spring stiffness are found such that the plate vibration is minimized. For this purpose, an optimal algorithm is developed based on mode summation approach. Results are presented...
Broadband, polarization-insensitive, and wide-angle optical absorber based on fractal plasmonics
, Article IEEE Photonics Technology Letters ; Volume PP, Issue 99 , 2016 ; 10411135 (ISSN) ; Abdollahramezani, S ; Chizari, A ; Khavasi, A ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2016
Abstract
In this paper, a plasmonic absorber consisting of a metal-dielectric-metal stack with a top layer of Sierpinski nanocarpet is theoretically investigated. Such a compact absorber depicts broadband angle-independent behavior over a wide optical wavelength range (400 700 nm) and a broad range of incidence angles (0 80). Including several feature sizes, such a fractal-like structure shows average simulated extinction response of 0:85 for either transverse electric or magnetic polarization states under normal incidence. Underlying mechanisms of absorbance due to excited surface plasmon modes as well as electric/magnetic dipole resonances are well revealed by investigating electric field, magnetic...
Taguchi optimized synthesis of collagen-g-poly(acrylic acid)/kaolin composite superabsorbent hydrogel
, Article European Polymer Journal ; Volume 44, Issue 4 , 2008 , Pages 1209-1216 ; 00143057 (ISSN) ; Ayyari, M ; Amini Fazl, M. S ; Sharif University of Technology
2008
Abstract
A novel biopolymer-based hydrogel composite was synthesized through chemical crosslinking by graft copolymerization of partially neutralized acrylic acid onto the hydrolyzed collagen. The Taguchi method, a robust experimental design, was employed for the optimization of the synthesis based on the swelling capacity of the hydrogels. This method was applied for the experiments and standard L16 orthogonal array with five factors and four levels. In the synthesis of the composite superabsorbent, N,N′-methylene bisacrylamide (MBA) as crosslinker, ammonium persulfate (APS) as initiator, acrylic acid (AA) as monomer, neutralization percent (NU), and collagen/kaolin weight ratio were used as...
An analytical and experimental study on dampening material effects on the dynamic behavior of free-free aluminum sheets
, Article Engineering Solid Mechanics ; Volume 9, Issue 2 , 2021 , Pages 111-122 ; 22918744 (ISSN) ; Hosseini Kordkheili, S. A ; Parviz, H ; Sharif University of Technology
Growing Science
2021
Abstract
This work aims to present an experimentally verified analytical solution to examine damping properties of systems including viscoelastic treatments. Although there are several methods for characterizing the behavior of three-layer damping systems, the RKU method is the most frequently used one. In this paper, this method is modified such a way that to be applied for a five-layer damping system. The achieved analytical relations are then employed to study the effects of a four-layer vibration-absorbing coating on the dynamic behavior of an aluminum sheet with free-free boundary conditions. Since the vibration-damping properties of the coating are unknowns, its loss factor and shear modulus...