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Broadband Electromagnetic Scattering and Shielding Analysis using the Finite-Difference Time-Domain Method
Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
2001 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis deals with numerical simulations of Maxwell's equations using the Finite-Difference Time-Domain (FDTD) method. The method is widely used in scattering, antenna and electromagnetic compatibility (EMC) applications.

A highly topical area in EMC analysis is Shielding Effectiveness (SE) simulations which is a measure of the (unintentional) coupling from outer electromagnetic sources into electrical components inside shielded electronic equipment. Even though the shielded enclosure and the components inside (e.g. printed circuit boards) can be resolved with FDTD, it is often impossible to resolve the apertures which cause the field penetration into the enclosure. The reason for this is that the apertures arc often much smaller than the resolution of the FDTD lattice and that the material properties at the aperture are often unknown (c.g gaskets, paint etc.). An important parameter in this context is the aperture transmission cross section which characterizes the electromagnetic properties of an aperture. Methods for extracting this parameter from FDTD simulations have been developed. Also, a semi-empirical method has been developed where the measured aperture transmission cross section can be parameterized and inserted in the numerical model as a point source representing the aperture.

An important parameter in radar applications is the Radar Cross Section (RCS) of a scattering object. FDTD is a suitable method for broadband simulations of the RCS. However, since only the volume in the vicinity of the object is included in the FDTD lattice, a near- to far-zone transformation must be applied for determining the far-field results. The transmitting source is also often in the far-zone, which implies that it can be approximated by a plane wave. A plane wave can be generated inside the FDTD lattice using the electromagnetic equivalence principle, or Huygens' sources. The thesis includes methods for improving both the near- to far-zone transformation and the plane wave excitation with respect to numerical dispersion. For Synthetic Aperture Radar (SAR) applications it is necessary to simulate the scattered field of objects placed on ground. The near- to far-zone transformation and the Huygens' sources have been extended to include a lossy dielectric homogeneous half-space representing the ground. A new timedomain version of the near- to far-zone transformation for this purpose has been developed which reduces the execution times significantly. The accuracy of plane wave excitation when a ground is present, has been improved by developing modified Fresnel coefficients consistent with the FDTD algorithm. The improvements provide the ability to simulate electromagnetic scattering of low amplitude using FDTD.

Place, publisher, year, edition, pages
Linköping: Linköping University , 2001. , p. 39
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 669
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:liu:diva-180150Libris ID: 8372565ISBN: 9172199148 (print)OAI: oai:DiVA.org:liu-180150DiVA, id: diva2:1601631
Public defence
1999-03-02, Planck, Fysikhuset, Linköpings universitet, Linköping, 14:15
Opponent
Note

All or some of the partial works included in the dissertation are not registered in DIVA and therefore not linked in this post.

Available from: 2021-10-08 Created: 2021-10-08 Last updated: 2023-03-09Bibliographically approved
List of papers
1. Dispersion compensation for Huygens' sources and far-zone transformation in FDTD
Open this publication in new window or tab >>Dispersion compensation for Huygens' sources and far-zone transformation in FDTD
2000 (English)In: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 48, no 4, p. 494-501Article in journal (Refereed) Published
Abstract [en]

The equivalence principle is utilized for generation of both incident plane waves and for near- to far-zone transformation in the finite-difference time-domain (FDTD) method. Small errors will appear due to numerical dispersion when a plane wave is generated by Huygens' sources using an analytical expression fur the incident field. These errors can be derived from the numerical dispersion relation in the frequency domain. By using a second-order approximation of the numerical wavenumber it is shown that a simple approximative time-domain compensation procedure for the dispersion can be derived. This has been implemented in a Huygens' source routine and in a time-domain near- to far-zone transformation routine. It is shown that this compensation significantly reduces the errors produced when calculating far-zone scattered fields of low amplitude. It is also shown that it is sufficient to compensate either the Huygens' sources or the time-domain near- to Far-zone transformation with respect to dispersion. For validation, plane wave propagation through empty space and scattering of a dipole have been studied.

Keywords
FDTD methods, numerical dispersion
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-49723 (URN)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2021-10-08
2. A coherent scattering model to determine forest backscattering in the VHF-band
Open this publication in new window or tab >>A coherent scattering model to determine forest backscattering in the VHF-band
2000 (English)In: IEEE Transactions on Geoscience and Remote Sensing, ISSN 0196-2892, E-ISSN 1558-0644, Vol. 38, no 1, p. 238-248Article in journal (Refereed) Published
Abstract [en]

A coherent scattering model to determine the forest radar backscattering at VHF frequencies (20-90 MHz) has been de developed. The motivation for studying this frequency band is the recent development of the CARABAS Synthetic Aperture Radar (SAR). In order to model the scattering from branches and trunks, homogeneous dielectric cylinders placed above a semi-infinite dielectric ground have been analyzed. An analytical approach, where the theoretically exact currents induced in an infinite cylinder are truncated, has been compared to a numerical solution using the finite difference time domain (FDTD) method, If the first-order coherent ray tracing is included in the analytical approach, the results match well with the numerically exact FDTD solution. The results show that, in order to determine the VHF-backscattering from a forest stand, the coherent ground interaction is an important part and has to be considered. In this paper, modeling results are in good agreement with CARABAS measurements.

Keywords
backscattering, CARABAS, forestry, modeling, synthetic aperture radar (SAR), VHF
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-49863 (URN)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2021-10-08

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