| 1. |
|
|
| 2. |
- Bernland, Anders, et al.
(författare)
-
Physical limitations on the scattering of electromagnetic vector spherical waves
- 2010
-
Rapport (övrigt vetenskapligt/konstnärligt)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.
|
|
| 3. |
- Fhager, Andreas, 1976, et al.
(författare)
-
Image Reconstruction in Microwave Tomography Using a Dielectric Debye Model
- 2012
-
Ingår i: IEEE Transactions on Biomedical Engineering. - 0018-9294 .- 1558-2531. ; 59:1, s. 156 - 166
-
Tidskriftsartikel (refereegranskat)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.
|
|
| 4. |
- Gustafsson, Mats, et al.
(författare)
-
Absorption Efficiency and Physical Bounds on Antennas
- 2010
-
Ingår i: International Journal of Antennas and Propagation. - : Hindawi Limited. - 1687-5869 .- 1687-5877. ; 2010
-
Tidskriftsartikel (refereegranskat)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.
|
|
| 5. |
- Gustafsson, Mats, et al.
(författare)
-
Antenna currents for optimal Q, superdirectivity, and radiation patterns using convex optimization
- 2012
-
Rapport (övrigt vetenskapligt/konstnärligt)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.
|
|
| 6. |
|
|
| 7. |
- Gustafsson, Mats, et al.
(författare)
-
Information fusion in electromagnetic sensing
- 2010
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We discuss information fusion in electromagnetic sensing with regard to the ISTIMES "Integrated System for Transport Infrastructure surveillance and Monitoring by Electromagnetic Sensing" project.
|
|
| 8. |
|
|
| 9. |
- Gustafsson, Mats, et al.
(författare)
-
Optimal Antenna Currents for Q, Superdirectivity, and Radiation Patterns Using Convex Optimization
- 2013
-
Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 61:3, s. 1109-1118
-
Tidskriftsartikel (refereegranskat)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 provide 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-fields are presented. The effects of antennas embedded in structures are also discussed. The results are illustrated for planar geometries.
|
|
| 10. |
|
|
