Sharif Digital Repository

An analysis is presented of the effective electromagnetic parameters of high-permittivity, anisotropic artificial dielectrics which are built by stacking arrays of metallic elements and conventional dielectric films, with adjacent arrays shifted with respect to each other. The effective parameters of the artificial dielectric are extracted from the scattering coefficients of plane electromagnetic waves which are normally or obliquely incident on a slab of the artificial material with finite thickness. These coefficients are derived from the generalised scattering matrix of a single layer of metallic elements which is computed using the integral equation technique. Both two-dimensional and... 

High-quality guided wave devices are key components in integrated millimeter-wave circuits. In this paper, we propose mm-wave planar dielectric waveguides based on thin, anisotropic artificial dielectric layers with very high in-plane permittivity. Waves propagating on such films are surface waves whose field exponentially decays outside the film in the vertical direction, similar to waveguides commonly used in integrated optics. The very high in-plane permittivity of the artificial dielectric layers leads to strong field confinement, and allows the implementation of relatively thin waveguides. This fact, together with the planar structure of these devices, make them highly suitable for... 

A new method is presented for the extraction of the bulk and surface parameters of a periodic artificial medium which uses the eigenvectors of the generalized transfer matrix of a unit layer. These eigenvectors correspond to the Bloch modes of the periodic structure. The eigenvector related to the propagating Bloch mode directly yields an expression for the effective, intrinsic wave impedance of the medium. Moreover, the interface between the artificial material and a surrounding, conventional (dielectric) region is described by an interface impedance matrix which accounts for the excitation of higher order, nonpropagating Bloch modes at the interface. Although these modes do not propagate... 

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... 

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... 

This paper presents a novel approach for designing dual-band absorbers based on graphene and metallic metasurfaces for terahertz and mid-infrared regimes, respectively. The absorbers are composed of a 2D array of square patches deposited on a dielectric film terminated by a metal plate. Using an analytical circuit model, we obtain closed-form relations for different parameters of the structure to achieve the dual-band absorber. Two absorption bands with an obtained absorptivity of 98% at 0.53 and 1.53 THz for the graphene-based structure and 7 and 25 THz for the metallic-based case are achieved. We demonstrate that the graphene-based absorber remains as the dual band for a wide range of the... 

The integral equation technique, in combination with the method of moments, is widely used for treating the electromagnetic scattering from periodic rough surfaces. This method, however, requires the computation of a kernel (a periodic Green's function) that consists of a slowly converging infinite series of conventional Green's functions. To accelerate the convergence of this series, different methods have been proposed in literature. In this paper, we use a complex image (CI) technique to find a closed-form expression for the periodic Green's function, which is then used to analyze the electromagnetic scattering from arbitrary periodic rough surfaces. The resulting CI Green's function... 

Eelectromagnetic analysis of periodic structures is important in the electromagnetic theory. Among them, the electromagnetic wave scattering analysis from rough surfaces is of importance due to both theoretical and practical points of view. For slow variation periodic surfaces the solution can be obtained under the Rayleigh hypothesis in terms of Floquet modes [1]. Integral equation approaches in combination with the method of Moments are among the most frequently used in the solution of scattering problems related to periodic surface due to their flexibility in modeling different geometries [2-3]. Due to slowly convergence of infinite series periodic Green's function, these methods need... 

In this paper, an analytical circuit model is proposed for 2-D arrays of graphene disks. First, we derive an analytical expression for the surface current density on a single graphene disk in the subwavelength regime, induced by a normally incident plane wave. The solution is then extended to 2-D arrays of graphene disks using perturbation theory. Finally, by applying appropriate boundary conditions, an R - L - C equivalent circuit of the structure is obtained. It is shown that both a single graphene disk and periodic array of graphene disks have dual capacitive-inductive nature. The results of the proposed model are in excellent agreement with those obtained by full-wave simulations  

In this paper, we extract the fundamental resonant mode of a graphene patch using a variational method. We use 2-D eigenvalue problem obtained from the integral equation governing the surface current on graphene patterns under quasi-static approximation. To compute the eigenvalues, we propose three trial eigenfunctions, which meet the boundary conditions. We investigate the accuracy of these eigenfunctions with comparing to the results obtained by full wave simulations. Finally, we analyze square-lattice arrangements of graphene patches using the most accurate proposed eigenfunction and derive a very accurate surface impedance for it. The proposed surface impedance is much more precise than... 

Digital Elevation Models (DEMs) play a significant role in hydraulic modeling and flood risk management. This study initially investigated the effect of Unmanned Aerial Vehicle (UAV) DEM resolutions, ranging from 1 m to 30 m, on flood characteristics, including the inundation area, mean flow depth, and mean flow velocity. Then, the errors of flood characteristics for global DEMs, comprising ALOS (30 m), ASTER (30 m), SRTM (30 m), and TDX (12 m) were quantified using UAV DEM measurements. For these purposes, the HEC-RAS 2D model in steady-state conditions was used to simulate the flood with return periods of 5- to 200 years along 20 km reach of Atrak River located in northeastern Iran.... 

This study investigated the lake–aquifer hydraulic interactions in Lake Urmia (LU) as the second largest hypersaline lake in the world. Due to the scarcity of hydrogeological data required for modelling, a method based on Darcy’s Law and lake water budget was used to quantify the lake–aquifer interaction. Long-term ground- and satellite-based hydrological datasets over the time frame 2001–2019 were used. Results indicate that the groundwater flux between LU and the aquifers controls 18.74 ± 1.67% of the lake’s water storage. While 10 out of 14 adjacent aquifers recharge LU at a rate of less than 180 m3/m.month, one phreatic aquifer recharges the LU up to 1400 m3/m.month. Two aquifers are... 

Novel types of highly swelling hydrogels (superabsorbent) were prepared by grafting crosslinked poly acrylic acid-co-2-hydroxyethylmetacrylate (PAA-co-HEMA) chains onto starch through a free radical polymerization method. The effect of grafting variables (i.e., concentration of methylenebisacrylamide (MBA), acrylic acid/2-hydroxy methymetacrylate (AA/HEMA) weight ratio, ammonium persulfate (APS), starch, neutralization percent, were systematically optimized to achieve a hydrogel with a maximum swelling capacity. The superabsorbent (SAP) formation was confirmed by Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The controlled-release behavior of... 

In this study a review of the developed methods to estimate groundwater withdrawal (GWW) from aquifers by pumping wells is provided. Then, a method adopted by Iran's Basic Studies Bureau of Water Resources Management Company for estimation of GWW through 536 aquifers across Iran is presented and modified. This so-called “representative pumping wells network” (RPWN) approach is a combination of statistical and rate-and-time methods which has been implemented for all aquifers in Iran since 2007. The RPWN approach is based on the overlaying of 10 important features in a GIS environment and classified in a number of zones in which their withdrawals are statistically different. The representative... 

In this study, a review of the overlay/index methods served for delineation of vulnerable zones in coastal aquifers affected by SWI is provided. Then, a more realistic presentation of the vulnerability mapping of coastal aquifers to SWI through modified GALDIT index method by incorporating the influential factors on SWI is established. The modifications on GALDIT method including incorporating the seaward hydraulic gradient (i) instead of the height of groundwater level above sea level (L) (so-called GAiDIT), and considering hydraulic gradient (i) as an additional parameter to the GALDIT (so-called GALDIT-i). Three GALDIT, GAiDIT, and GALDIT-i methods were evaluated with data from three... 

The estimation of long-term groundwater recharge rate (GWr) is a pre-requisite for efficient management of groundwater resources, especially for arid and semi-arid regions. Precise estimation of GWr is probably the most difficult factor of all measurements in the evaluation of GW resources, particularly in semi-arid regions in which the recharge rate is typically small and/or regions with scarce hydrogeological data. The main objective of this study is to find and assess the predicting factors of GWr at an aquifer scale. For this purpose, 325 Iran’s phreatic aquifers (61% of Iran’s aquifers) were selected based on the data availability and the effect of eight predicting factors were assessed... 

Petroleum industry is moving toward enhancing oil recovery methods, especially water-based methods, including low salinity and smart water flooding which water with an optimized composition is injected into the reservoir for improving oil recovery. Injection of water into the target formation is also a common operation in geothermal energy production. As the water is being injected into the reservoir, pressure and temperature change along the well column and cause scale formation. Mineral scale precipitation and deposition is a common problem for water injection wells which reduces the effective radius of the wellbore and affects the injection efficiency. In this paper, modeling scale... 

The Taguchi method, a robust experimental design, was used for optimization of synthesis of a novel biopolymer-based superabsorbent hydrogel, kappa-carrageenan (K-C)-g-acrylic acid (AA)-co-2-acrylamido-2- methylpropanesulfonic acid (AMPS). The Taguchi method was applied for the experimental and standard 18 orthogonal arrays (OA) with seven factors and three levels for each factor. In the synthesis of the superabsorbent, N,N'-methylene bisacrylamide (MBA) as crosslinker, ammonium persulfate (APS) as initiator, monomer ratio (AA/AMPS), K-C concentration, Total Monomer, neutralization percent (NU), and reaction temperature were used as important factors. After analyzing with analysis of...