| 1. |
- Dalarsson, Mariana, et al.
(författare)
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Exact analytical solution for fields in a lossy cylindrical structure with hyperbolic tangent gradient index metamaterials
- 2016
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Ingår i: Optical and quantum electronics. - : Springer Science and Business Media LLC. - 0306-8919 .- 1572-817X. ; 48:3
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Tidskriftsartikel (refereegranskat)abstract
- The advent of metamaterials with tailorable frequency dispersion ensured the emergence of transformation optics with proposed applications that include cloaking devices, superconcentrators, superabsorbers, beam shapers and benders, field and polarization rotators, etc. A crucial property of interest for transformation optics is the possibility to custom design the spatial dependence of optical properties, i.e. to attain a gradient of effective refractive index. The cylindrical geometry has been one of the prototypal proposed forms and actually the first theoretical and experimental cloaking devices had radial symmetry. In this contribution we present an exact analytical approach to the solution of Helmholtz' equations applied to radial propagation of electromagnetic waves through a cylinder containing negative and positive refractive index parts. A hyperbolic tangent gradient of refractive index is assumed. Our approach is inspired by the correspondence between transformation optics and quantum mechanics. A remarkably simple exact analytical solution is derived that takes into account realistic losses in negative-positive refractive index material composites.
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| 2. |
- Dalarsson, Mariana, et al.
(författare)
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Exact Analytical Solution for Fields in a Lossy Cylindrical Structure with Linear Gradient Index Metamaterials
- 2015
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Ingår i: Progress In Electromagnetics Research. - 1070-4698 .- 1559-8985. ; 151, s. 109-117
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the electromagnetic wave propagation across a finite inhomogeneous and anisotropic cylindrical metamaterial composite containing both positive and negative effective refractive index parts with linear spatial gradient. Exact analytical solutions for the electric and magnetic field distributions are obtained for a linear variation of effective refractive index across the structure. The exact analytical results for the electric and magnetic fields are compared to the numerical results obtained using the numerical simulation software HFSS. The model allows for general temporal dispersion and uniform losses within the composite.
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| 3. |
- Dalarsson, Mariana, et al.
(författare)
-
Exact analytical solution for fields in gradient index metamaterials with different loss factors in negative and positive refractive index segments
- 2013
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Ingår i: Journal of Nanophotonics. - 1934-2608. ; 7, s. 073086-
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Tidskriftsartikel (refereegranskat)abstract
- Gradient refractive index metamaterials are of interest for various applications of transformation optics. Wave propagation through gradient index metamaterials using an exact analytical approach is investigated. Composite materials containing constituents with negative real and positive real indexes of refraction are considered. An exact analytical solution for the field distribution is obtained for the sinusoidal spatial variation of complex effective permittivity and permeability along a fixed direction, under the assumption that the wave impedance remains spatially uniform across the structure. Loss factors in the constituent materials can be different from each other corresponding to the realistic situations. Temporal dispersion can be arbitrary subject to the physical limitations imposed by the Kramers-Kronig relations. A numerical model based on the Z-transform is developed to verify the analytical results. The approach can be applied to arbitrary periodic refractive index profiles using the Fourier series method.
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| 4. |
- Dalarsson, Mariana, et al.
(författare)
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Exact analytical solution for oblique incidence on a graded index interface between a right-handed and a left-handed material
- 2009
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Ingår i: Journal of Optoelectronic and Biomedical Materials. - 2066-0049. ; 1:4, s. 345-352
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Tidskriftsartikel (refereegranskat)abstract
- We have determined the scattering parameters of optical structures incorporating both left-handed metamaterials (LHM) and conventional ("right-handed") materials (RHM) for the case when the refractive index at the LHM-RHM interface is graded, for oblique incidence at an arbitrary angle and for arbitrary spectral dispersion. We derived an accurate analytical solution to Helmholtz' equation for the case of the refractive index gradient varying as a hyperbolic tangent where the steepness of the index transition may be arbitrary, even of the order of vacuum wavelength. We determined the expressions for the field intensity along the LHM-RHM structure with refractive index gradient. We show that there is an excellent agreement between our analytical results and the accurate numerical simulations done by finite element method.
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| 5. |
- Dalarsson, Mariana, et al.
(författare)
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Lossy gradient index metamaterial with sinusoidal periodicity of refractive index : case of constant impedance throughout the structure
- 2011
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Ingår i: J NANOPHOTONICS. - : SPIE-Intl Soc Optical Eng. - 1934-2608. ; 5, s. 051804-
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Tidskriftsartikel (refereegranskat)abstract
- We used an exact analytical approach to investigate the electromagnetic wave propagation across an isotropic metamaterial composite with i. a sinusoidally periodic gradient of the real parts of the effective permittivity and permeability, ii. spatially uniform imaginary parts of the effective permittivity and permeability, and iii. spatially uniform impedance. The real part of the effective refractive index can be positive and negative along the direction of nonhomogeneity. A remarkably simple direct solution for the field distribution was obtained.
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| 6. |
- Dalarsson, Mariana, et al.
(författare)
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Phase Integral Approach to Wave Propagation in Continuously Graded Models of Flat Lenses
- 2017
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Ingår i: 2017 13th International Conference on Advanced Technologies, Systems and Services in Telecommunications (TELSIKS). - Piscataway, NJ : IEEE. - 9781538618004 ; , s. 38-41
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Konferensbidrag (refereegranskat)abstract
- We propose a method to determine approximate phase-integral analytical solutions for electric and magnetic fields in flat lenses with the refractive index varying in the radial direction. In our model the gradient of refractive index is approximated by a large number of concentric annuli with step-increasing index. Here the central part contributes to a bulk of the phase transformation, while the external layers act as a graded antireflective structure, matching the impedance of the lens to that of the free space. Such lenses can be modeled as compact composites with continuous permittivity and (if needed) permeability functions which asymptotically approach unity at the boundaries of the composite cylinder. We illustrate the phase-integral approach by obtaining the approximate analytic solutions for the electric and magnetic fields for a special class of composite designs with radially graded parameters.
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| 7. |
- Dalarsson, Mariana, et al.
(författare)
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Structures Containing Left-Handed Metamaterials with Refractive Index Gradient : Exact Analytical Versus Numerical Treatment
- 2009
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Ingår i: Microwave Review. - Belgrade, Serbia : Society for Microwave Technique, Technologies and Systems. - 1450-5835. ; 15:2, s. 2-5
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Tidskriftsartikel (refereegranskat)abstract
- We investigated propagation of electromagnetic waves through composite structures with negative refractive index, the popular ”left-handed metamaterials”, for the case when there is a gradient of refractive index. We obtained the exact analytical solutions to the Helmholtz equation valid for arbitrary steepness of the graded interface between the positive and the negative index part. We analyzed the special case of matched impedances of the two constituent materials within the metamaterial composite. We derived analytical expressions for the field intensity, transmission and reflection coefficients and compared them with the results obtained by the numerical simulations using the Finite Element Method. The model allows for arbitrary spectral dispersion and lossy media.
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| 8. |
- Hamed, Tareq Abu, et al.
(författare)
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Multiscale in modelling and validation for solar photovoltaics
- 2018
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Ingår i: EPJ Photovoltaics. - : EDP Sciences. - 2105-0716. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Photovoltaics is amongst the most important technologies for renewable energy sources, and plays a key role in the development of a society with a smaller environmental footprint. Key parameters for solar cells are their energy conversion efficiency, their operating lifetime, and the cost of the energy obtained from a photovoltaic system compared to other sources. The optimization of these aspects involves the exploitation of new materials and development of novel solar cell concepts and designs. Both theoretical modeling and characterization of such devices require a comprehensive view including all scales from the atomic to the macroscopic and industrial scale. The different length scales of the electronic and optical degrees of freedoms specifically lead to an intrinsic need for multiscale simulation, which is accentuated in many advanced photovoltaics concepts including nanostructured regions. Therefore, multiscale modeling has found particular interest in the photovoltaics community, as a tool to advance the field beyond its current limits. In this article, we review the field of multiscale techniques applied to photovoltaics, and we discuss opportunities and remaining challenges.
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