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| 2. |
- Fhager, Andreas, 1976, et al.
(författare)
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A statistical approach to gradient scaling microwave tomography
- 2007
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Ingår i: Proceedings of EMB 07, computational electromagnetis, methods and applications, Lund, Sweden. ; , s. 153-160, s. 153-160, s. 153-160
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 3. |
- Fhager, Andreas, 1976, et al.
(författare)
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A Statistically Based Preconditioner for Two-Dimensional Microwave Tomography
- 2007
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Ingår i: Proceedings of The Second International Workshop on Computational Advances in Multi-Sensor Adaptive Processing (CAMSAP2007), Dec. 12-14 2007, St. Thomas, U.S. Virgin Islands. - 9781424417148 ; , s. 173-176
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 4. |
- Nordebo, Sven, et al.
(författare)
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A Systematic Approach to Robust Preconditioning for Gradient Based Inverse Scattering Algorithms
- 2008
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Ingår i: Inverse Problems. - : IOP Publishing. - 1361-6420 .- 0266-5611. ; 24:2, s. 025027-
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a systematic approach to robust preconditioning for gradient-based nonlinear inverse scattering algorithms. In particular, one- and two-dimensional inverse problems are considered where the permittivity and conductivity profiles are unknown and the input data consist of the scattered field over a certain bandwidth. A time-domain least-squares formulation is employed and the inversion algorithm is based on a conjugate gradient or quasi-Newton algorithm together with an FDTD-electromagnetic solver. A Fisher information analysis is used to estimate the Hessian of the error functional. A robust preconditioner is then obtained by incorporating a parameter scaling such that the scaled Fisher information has a unit diagonal. By improving the conditioning of the Hessian, the convergence rate of the conjugate gradient or quasi-Newton methods are improved. The preconditioner is robust in the sense that the scaling, i.e. the diagonal Fisher information, is virtually invariant to the numerical resolution and the discretization model that is employed. Numerical examples of image reconstruction are included to illustrate the efficiency of the proposed technique. © 2008 IOP Publishing Ltd.
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| 5. |
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| 6. |
- Nordebo, Sven, et al.
(författare)
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Sensitivity analysis for antenna near-field imaging
- 2007
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Ingår i: IEEE Transactions on Signal Processing. - 1053-587X. ; 55:1, s. 94-101
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Tidskriftsartikel (refereegranskat)abstract
- Although imaging and inverse scattering problems have been thoroughly studied during the last century, there is only a partial understanding of these complex problems. Most of the efforts have been placed on the development of efficient inversion algorithms and mathematical uniqueness results. In comparison, there are very few results and a limited knowledge about the information content in the inversion data. In this paper, we provide a mathematical framework for sensitivity analysis of antenna near-field imaging problems, based on the multipole expansion of the electromagnetic field and the Fisher information to quantify the quality of data. By exploiting this framework, a fundamental relation for accuracy and resolution is formulated based on the Cramer-Rao bound (CRB). The sensitivity analysis is illustrated using a relevant example with cylindrical measurement data.
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| 7. |
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| 8. |
- Persson, Kristin, et al.
(författare)
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Experimental validation of reconstructed equivalent currents on a radome
- 2005
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Ingår i: [Host publication title missing]. - 8495999722 ; , s. 35-40
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Konferensbidrag (refereegranskat)abstract
- Knowledge of the current distribution on a radome can be used to improve radome design, detect manufacturing errors, and to verify numerical simulations. In this paper, the transformation from near-field data to its equivalent current distribution on a surface of arbitrary material, ie the radome, is analyzed. The transformation is based on a vector surface integral representation that relates the equivalent currents to the near-field data. Experimental verification using measured near-field data originating from a reflector antenna is then examined. The field irradiates a radome whereupon it is measured on a cylindrical surface. The quantity of data is large since the height of the radome corresponds to 29-43,,wavelengths in the frequency interval 8.0-12.0,,GHz. The presence of axial symmetry enables usage of the fast Fourier transform (FFT) to reduce the computational complexity. Furthermore, the problem is regularized using the singular value decomposition (SVD).
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| 9. |
- Persson, Kristin, et al.
(författare)
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Identification of the current distribution on a radome from near-field measurements
- 2002
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Ingår i: Proceedings radiovetenskap och kommunikation. - 1400-9137. ; , s. 392-395
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Information about the equivalent current distribution on a radome can be used to improve radome design, detect manufacturing errors, and to verify numerical simulations. In this paper, the transformation from near-field data to the equivalent current distribution is analyzed. The transformation is based on a singular value decomposition of the surface integral equation that relates the equivalent current to the near-field data. The attempt is to develop a mathematical model that easily can be used for arbitrary geometric structures. The symmetries of a specific problem is used to reduce the computational complexity. Both synthetic data and measured data are used to verify the algorithm.
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| 10. |
- Persson, Kristin, et al.
(författare)
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Near field to equivalent currents transformation with radome applications
- 2004
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Ingår i: Proceedings International Symposium on Electromagnetic Theory. - 8884922526 ; , s. 1122-1124
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Konferensbidrag (refereegranskat)abstract
- Knowledge about the equivalent currents distribution on a radome can be used to improve radome design, detect manufacturing errors, and to verify numerical simulations. In this paper, the transformation from near-field data to the equivalent currents distribution is analyzed. The transformation is based on a singular value decomposition of the surface integral equation that relates the equivalent currents to the near-field data. The mathematical model can easily be used for arbitrary geometric structures. The symmetries of a specific problem are utilized to reduce the computational complexity. Both synthetic data and measured data are used to verify the algorithm
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