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Optics Express (10944087)33(3)pp. 4550-4562
All-optical switches (AOSs) with the unique functionality of light controlling by light are the essential components of advanced photonics. However, it is still a grand challenge to propose materials with appropriate nonlinear effects and structures with high-performance all-optical switching. This study proposes an AOS with a hybrid silica-azopolymer optical microfiber coupler configuration. This structure is characterized by in-line switching functionality, extremely high extinction ratio of 22 dB at λ = 1550 nm, low-insertion loss (<1 dB), and ease of fabrication process. It is shown that, because of the photo-induced birefringence in the azopolymer microfiber, the functionality of the introduced switch depends on the polarizations of the controlling and propagating light signals. Moreover, using full-wave electromagnetic simulations, the performance of the hybrid AOS is explained and clarified. © 2025 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement.
IEEE Sensors Journal (1530437X)24(24)pp. 40994-41002
Optical microfiber couplers (OMCs) with simple structure, low loss, and high sensitivity have been broadly involved in physicochemical fiber sensing applications. Until now, the fabrication of OMCs using arc discharge as a fast, clean, and low-cost method has not been explored. In this study, an arc-discharge fiber heating and pulling process for OMC manufacturing is presented and the characteristics of the arc-induced structures are investigated. It is shown that, in addition to high spectral visibility and refractive index (RI) sensitivity, importantly, the arc-induced OMCs exhibit ultralow temperature dependency of less than 1.9 pm/°C, over the wide testing range of 15 °C to 315 °C. Finally, an exact theoretical explanation is presented for the observed different temperature coefficients using analytical expressions and full-wave simulations based on the modal analysis of OMCs. Thus, the introduced arc-discharge technique and the resultant OMCs with ultralow temperature dependency could be useful for real-world applications of microfiber (MF) couplers. © 2001-2012 IEEE.
CES Transactions on Electrical Machines and Systems (20963564)8(4)pp. 404-413
In this manuscript, a new axial-flux permanent-magnet machine (AFPMM) is designed, analyzed, improved, and successfully tested. A double-sided AFPM generator with four layers of stator winding is initially designed using a well-known quasi-3D analytical method. Then, the designed machine is simulated using commercial software. It is shown that modification techniques are required to improve the performance of both the torque ripple and the ratio of the third to the fundamental harmonics of the induced voltage. Therefore, a new improvement technique is proposed, in which the layers of the stator winding are shifted relative to each other. While this new technique significantly improves the third harmonic problem, the design still has a high torque ripple and, thus, it is suggested to combine the proposed method with the conventional magnet shifting technique. It is revealed numerically that the resulting combination properly resolves both third harmonic and torque ripple problems. Therefore, this design is considered the main design of the present manuscript. In the end, a prototype of the main design is manufactured and tested. It is shown that the measurement results are in good agreement with those of numerical software.①. © 2024 CES.
Chemical Engineering Journal (13858947)496
Nowadays, water and energy crises are important worldwide challenges. Many efforts have been devoted to develop efficient photothermal membranes for water desalination based on membrane distillation (MD) using renewable solar energy. In the way of investigating the parameters influencing MD, photothermal membranes with different surface morphologies were prepared based on electrospinning and casting techniques by changing the relevant parameters. For this purpose, solutions containing carbon black nanoparticles were used. The long-term photothermal vacuum MD (PVMD) performance of the membranes was guaranteed by omniphobic modification of surface using low-pressure plasma polymerization of perfluorooctyl acrylate monomers. It was well demonstrated that membrane surface morphology (roughness and porosity) and its photothermal activity are linearly correlated with coefficients of determination (R2) more than 0.9. In other words, membrane with efficient PVMD performance is expected provided that the membrane surface morphology is sufficiently rough and porous to enhance light absorption and trapping and simultaneously create the lowest and highest resistance against transfer of water molecules and wetting, respectively. The membrane with designed surface morphology (average roughness of 306.7 nm and porosity of 32.6 %) exhibited the most enhanced photothermal activity with evaporation efficiency as high as 93.5 %. Reducing average surface roughness and porosity to 101.1 nm and 5 %, respectively, led to a membrane with inferior PVMD performance and low evaporation efficiency as 60.7 %. The membrane with optimal performance exhibited a permeate flux of 2.85 kg/m2·h. This membrane also provided long-term performance against wetting by the feed solution containing 0.6 mM sodium dodecyl sulfate for 540 min. © 2024 Elsevier B.V.
IEEE Transactions on Antennas and Propagation (15582221)71(9)pp. 7376-7386
The reflection tensor of a metafilm with bianisotropic elements on a dielectric interface is analytically derived. First, using the dipole approximation, the nanoparticles are replaced with electric and magnetic dipoles. Next, the local fields are obtained as the superposition of the background field and the interaction fields (sum of fields by all dipoles and their images). The latter is written in a form that directly results in either fast-converging series or series with closed-form solutions. Utilizing the local fields, the collective polarizability tensor and the dipole intensities are determined. Then, assuming the array to be dense, the dipole array is replaced with current sheets, for which the radiated fields in the presence of a substrate are well-known. Next, the reflection tensor is derived, validated, and discussed. Moreover, using a numerical scheme, the polarizability tensor of a bianisotropic nanoparticle in free space is calculated. Using the computed polarizability tensor and the derived analytical expressions, reflection from a metafilm with bianisotropic nanoparticles on an interface is obtained. Finally, the more complex problems of embedded particles and oblique illumination are briefly addressed. © 1963-2012 IEEE.
Optics Express (10944087)29(20)pp. 31296-31310
Scattering from a chiral sphere above a lossy half-space, which could be of interest in remote sensing and optics, is analytically examined. The proposed method combines the vector Mie solution and the field transformations between vector spherical functions (VSFs) and plane waves (PWs). Using the reflection coefficients of the half-space and vector Mie solution for the chiral sphere, the first-order Mie field together with a relation between the Mie fields of successive orders are derived. The total Mie field is obtained as a series solution which is next converted to a non-recursive formulation. The scattered field is written as the sum of the total Mie field and its reflection from the half-space. The derived expressions are numerically validated. Some explanations based on the series solution are given and numerical results for different cases are presented and briefly discussed. © 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
OSA Continuum (25787519)4(12)pp. 3004-3013
The effect of stratified substrates on scattering from a chiral sphere is analytically and numerically examined. A combination of vector Mie solution and the field transformations between vector spherical functions (VSFs) and plane waves (PWs) is used to determine the scattered fields of different orders. The generalized reflection coefficients of the stratified half-space and vector Mie solution for the chiral sphere are used to calculate successive interactions of the sphere and the interface and a series solution is obtained. Commercial software FEKO is used to numerically validate the derived expressions for the multilayered substrate. Various numerical results are presented and discussed. Specifically, a slab with exponential profile is considered as an example of an inhomogeneous substrate and its scattering coefficients are compared with the homogeneous case. © 2021 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
IEEE Transactions on Antennas and Propagation (15582221)66(1)pp. 347-359
Analytical expressions for the scattering coefficients of a dielectric sphere buried under a rough interface are presented. The proposed method combines the small perturbation method (SPM) and the Mie solution by using the expansion of plane waves in terms of vector spherical functions (VSFs) and vice versa. First, using SPM, the zeroth-and the first-order perturbative scattered fields of a rough interface for illuminations from above and below are derived. Using these solutions, the field transmitted to the lower half-space is determined as a spectrum of down-going plane waves. The scattered fields from the sphere are then calculated using the vector Mie solution. Subsequently, the VSFs are expanded in terms of up-going plane waves. These plane waves illuminate the interface, and using SPM, the scattered fields in the upper and lower regions are determined as infinite summations of plane waves. The reflected plane waves are once again scattered by the sphere and the scenario repeats. By inspecting the form of the fields resulting from the few first interactions of the sphere and the rough interface, a recursive form is obtained for the scattered fields. This recursive form is then used to rewrite the system of equations in a form containing all interactions in a single-step formulation. Accordingly, the zeroth-and the first-order closed-form scattered fields are obtained. The derived expressions are analytically and numerically validated. Finally, the numerical results for the case of the rough interface with sinusoidal profile are presented and briefly discussed. © 1963-2012 IEEE.
IEEE Transactions on Geoscience and Remote Sensing (15580644)54(6)pp. 3685-3692
The first-order perturbative solution of scattering from layered rough surfaces is investigated numerically and analytically. The analytical solution is obtained using a small perturbation approach based on the extended boundary conditions (EBCs). Recently, the first-order scattering solution of a two-rough-surface structure with inhomogeneous dielectric profiles was derived using an EBC-based small perturbation method. In this paper, using those solutions and utilizing the Bragg scattering nature of the first-order perturbative solutions, the problem of scattering from a multi-rough-surface structure is solved straightforwardly. The derived first-order elements of the scattering matrix are simplified and rewritten explicitly in terms of the generalized reflection and transmission coefficients. Due to the simple form of the final solutions, they are easily interpreted in terms of simple scattering mechanisms. Then, the solutions are numerically evaluated for three-layer rough surfaces with different subsurface parameters. It is observed that the difference normalized radar cross sections follow definite simple patterns as the subsurface characteristics are changed. Finally, these variation patterns, which could be of interest in inverse scattering problems, are analytically explained using the derived theoretical solutions. Indeed, the solutions are expressed in forms in which the terms responsible for the observed patterns are explicitly distinguished. © 2016 IEEE.
IEEE Transactions on Antennas and Propagation (15582221)64(5)pp. 1877-1890
An analytical solution for the cross-polarized scattering from multilayered media with an arbitrary number of rough interfaces is presented. The second-order perturbative solutions are summations of the Fourier transform pair products of the roughness profiles, and hence, the problem is initially reduced to two generic problems: one with just a single rough surface with two stratified media above and below it and another with two rough interfaces with three stratified media above, between, and below them. The former helps find the second-order contribution of an individual rough interface while the latter is intended to determine the interaction contribution of two arbitrary rough interfaces. In this paper, the second generic problem is solved using the small perturbation method (SPM) based on the extended boundary conditions (EBC). In this SPM formulation, the stratifications are easily accounted for using the generalized coefficients inserted in the dyadic Green's functions (DGFs). Then, the expressions are simplified to find the solution of the first generic problem which is a special case of the second one. Next, the explicit expressions of the generalized coefficients are introduced to the solutions. Subsequently, the interaction terms of the second and the self-term of the first generic problem are combined to find the desired second-order solution. Finally, using the solution derived, a few numerical examples are presented. © 2016 IEEE.
Mirjahanmardi s.h., ,
Tavakoli, A.,
Zamani, H.,
Dehkhoda, P. AP-S International Symposium (Digest) (IEEE Antennas and Propagation Society) (15223965)2015pp. 506-507
In this paper, radar cross section (RCS) of a buried sphere below a two-layer rough surface is studied by implementing a finite difference time domain (FDTD) code. The effect of the sphere size is studied at different observing angles. © 2015 IEEE.
IEEE Transactions on Antennas and Propagation (15582221)63(12)pp. 5753-5766
A rigorous analytical technique to derive the scattering coefficients of three-dimensional (3-D) two rough surfaces with arbitrary dielectric profiles is presented. The proposed method applies a perturbation approach to a surface integral equation (IE) formulation that is derived from the extended boundary conditions (EBC). First, using EBC or the surface equivalence principle (SEP) and the dyadic Green's functions of the resulting simpler geometries, a system of IEs for the surface fields of the two rough interfaces is established. Then, the Fourier-domain surface fields are derived using a perturbation method. The scattered fields are subsequently determined by a second application of SEP. In general, the approach could be used to present the general formulation for multiple rough layers and also higher order solutions. But, the focus of this paper is on deriving compact closed-form solutions for inhomogeneous dielectric profiles and thus, only two rough interfaces are considered. Accordingly, the first-order closed-form scattered fields are represented in a remarkably compact form that is suitable for physical interpretation and also extension to higher orders. Finally, the derived expressions are compared to known solutions of special cases, available in the literature. The results are shown to be exactly consistent with existing ones and hence validated analytically and numerically. © 2015 IEEE.
IEEE Transactions on Antennas and Propagation (15582221)63(12)pp. 5767-5776
Analytical expressions for the cross-polarization components of the normalized radar cross sections (NRCS) of three-dimensional stratified media with two rough surfaces are presented. In a recent paper, the zeroth- and the first-order scattering solutions of a two-rough-surface structure with arbitrary dielectric profiles were presented using the small perturbation approach based on the extended boundary conditions (EBC). In this study, the proposed method is extended to obtain the second-order solutions including cross-polarized fields. Unlike copolarizations, the main contribution of cross-polarizations is determined by the second-order solutions. A direct extension of the recently proposed formulation leads to difficult and lengthy manipulations; hence, first a compact recursive matrix formulation for the unknown surface fields of an arbitrary order is derived. Then, for the second-order fields, the matrix system is efficiently and straightforwardly solved. Finally, the cross-polarized scattered fields and the normalized radar cross sections are derived. The final solutions are given in simple, compact, and closed-form expressions that make the computations very easy. The derived expressions are validated against known solutions of special cases, available in the literature. The results are shown to be exactly consistent with existing ones, both analytically and numerically. © 2015 IEEE.
