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| 2. |
- Bernland, Anders, et al.
(author)
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Physical limitations on the scattering of electromagnetic vector spherical waves
- 2010
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Reports (other academic/artistic)abstract
- Understanding the interaction between electromagnetic waves and matter is vital in applications ranging from classical optics to antenna theory. This paper derives physical limitations on the scattering of electromagnetic vector spherical waves. The assumptions made are that the heterogeneous scatterer is passive, and has constitutive relations which are on convolution form in the time domain and anisotropic in the static limit. The resulting bounds limit the reflection coefficient of the modes over a frequency interval, and can thus be interpreted as limitations on the absorption of power from a single mode. They can be used within a wide range of applications, and are particularly useful for electrically small scatterers. The derivation follows a general approach to derive sum rules and physical limitations on passive systems on convolution form. The time domain versions of the vector spherical waves are used to describe the passivity of the scatterer, and a set of integral identities for Herglotz functions are applied to derive sum rules from which the physical limitations follow.
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| 3. |
- Bernland, Anders, et al.
(author)
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Summation rules and physical bounds for partial wave scattering in electromagnetics
- 2009
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In: [Host publication title missing]. ; , s. 206-207
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Conference paper (peer-reviewed)abstract
- A general approach to derive summation rules in electromagnetics using Herglotz functions is presented in this paper. This approach is then used to obtain summation rules and bounds on partial wave scattering, which are illustrated numerically by the scattering of a Drude sphere.
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| 4. |
- Fhager, Andreas, 1976, et al.
(author)
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A statistical approach to gradient scaling microwave tomography
- 2007
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In: Proceedings of EMB 07, computational electromagnetis, methods and applications, Lund, Sweden. ; , s. 153-160, s. 153-160, s. 153-160
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Conference paper (other academic/artistic)
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| 5. |
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| 6. |
- Fhager, Andreas, 1976, et al.
(author)
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Image Reconstruction in Microwave Tomography Using a Dielectric Debye Model
- 2012
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In: IEEE Transactions on Biomedical Engineering. - 0018-9294 .- 1558-2531. ; 59:1, s. 156 - 166
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Journal article (peer-reviewed)abstract
- In this paper, quantitative dielectric image reconstruction based on broadband microwave measurements is investigated. A time-domain-based algorithm is derived where Debye model parameters are reconstructed in order to take into account the strong dispersive behavior found in biological tissue. The algorithm is tested with experimental and numerical data in order to verify the algorithm and to investigate improvements in the reconstructed image resulting from the improved description of the dielectric properties of the tissue when using broadband data. The comparison is made in relation to the more commonly used conductivity model. For the evaluation, two examples were considered, the first was a lossy saline solution and the second was less lossy tap water. Both liquids are strongly dispersive and used as a background medium in the imaging examples. The results show that the Debye model algorithm is of most importance in the tap water for a bandwidth of more than 1.5 GHz. Also the saline solution exhibits a dispersive behavior but since the losses restrict the useful bandwidth, the Debye model is of less significance even if somewhat larger and stronger artifacts can be seen in the conductivity model reconstructions.
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| 7. |
- Gustafsson, Mats, et al.
(author)
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Absorption Efficiency and Physical Bounds on Antennas
- 2010
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In: International Journal of Antennas and Propagation. - : Hindawi Limited. - 1687-5869 .- 1687-5877. ; 2010
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Journal article (peer-reviewed)abstract
- Abstract—The all spectrum absorption efficiency appears in the physical bounds on antennas expressed in the polarizability dyadics. Here, it is shown that this generalized absorption efficiency is close to 1/2 for small idealized dipole antennas and for antennas with a dominant resonance in their absorption. Also, the usefulness of this parameter is analyzed for estimation of antenna performance. The results are illustrated with numerical data for several antennas.
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| 8. |
- Gustafsson, Mats, et al.
(author)
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An overview of some recent physical bounds in scattering and antenna theory
- 2009
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In: ; , s. 1715-1718
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Conference paper (peer-reviewed)abstract
- The objective of this paper is to give an overview of some recently developed sum rules and physical bounds in scattering and antenna theory. The sum rules are based on integral identities for Herglotz functions that relate the quantity of interest with its low and high-frequency behavior. The sum rules are transformed to bounds by estimating the integrals and applying variational results to the parameters that appear in the asymptotic expansions. The theoretical findings are exemplified by numerical results for various scattering and antenna configurations.
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| 9. |
- Gustafsson, Mats, et al.
(author)
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Antenna Current Optimization using MATLAB and CVX
- 2016
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In: FERMAT. ; 15
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Journal article (peer-reviewed)abstract
- Antenna current optimization is a tool that offers many possibilities in antenna technology. Optimal currents are determined in the antenna design region and used for physical understanding, as a priori estimates of the possibilities todesign antennas, physical bounds and as figures of merits for antenna designs. Antenna current optimization is particularly useful for small antennas and antennas that are constrained by their electrical size. The initial non-convex antenna design optimization problem is reformulated as a convex optimizationproblem expressed in the currents on the antenna. This convex optimization problem is solved efficiently at a computational cost comparable to a Method of Moments (MoM) solution of the same geometry. In this paper a tutorial description of antenna current optimization is presented. Stored energies and their relation to the impedance matrix in MoM is reviewed. The convex optimization problems are solved using MATLAB and CVX. MoM data isincluded together with MATLAB and CVX codes to optimize the antenna current for strip dipoles and planar rectangles. Codes and numerical results for maximization of the gain to Q-factor quotient and minimization of the Q-factor for prescribed radiated fields are provided.
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| 10. |
- Gustafsson, Mats, et al.
(author)
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Antenna currents for optimal Q, superdirectivity, and radiation patterns using convex optimization
- 2012
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Reports (other academic/artistic)abstract
- The high Q-factor (low bandwidth) and low efficiency make the design of small antennas challenging. Here, convex optimization is used to determine current distributions that give upper bounds on the antenna performance. Optimization formulations for maximal gain Q-factor quotient, minimal Q-factor for superdirectivity, and minimum Q for given far-field are presented. The effects of antennas embedded in structures are also discussed. The results are illustrated for planar geometries.
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