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Direct and Inverse Methods for Waveguides and Scattering Problems in the Time Domain
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för teknisk databehandling. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Numerisk analys.
2005 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

Numerical simulation is an important tool in understanding the electromagnetic field and how it interacts with the environment. Different topics for time-domain finite-difference (FDTD) and finite-element (FETD) methods for Maxwell's equations are treated in this thesis.

Subcell models are of vital importance for the efficient modeling of small objects that are not resolved by the grid. A novel model for thin sheets using shell elements is proposed. This approach has the advantage of taking into account discontinuities in the normal component of the electric field, unlike previous models based on impedance boundary conditions (IBCs). Several results are presented to illustrate the capabilities of the shell element approach.

Waveguides are of fundamental importance in many microwave applications, for example in antenna feeds. The key issues of excitation and truncation of waveguides are addressed. A complex frequency shifted form of the uniaxial perfectly matched layer (UPML) absorbing boundary condition (ABC) in FETD is developed. Prism elements are used to promote automatic grid generation and enhance the performance. Results are presented where reflection errors below -70dB are obtained for different types of waveguides, including inhomogeneous cases. Excitation and analysis via the scattering parameters are achieved using waveguide modes computed by a general frequency-domain mode solver for the vector Helmholtz equation. Huygens surfaces are used in both FDTD and FETD for excitation in waveguide ports.

Inverse problems have received an increased interest due to the availability of powerful computers. An important application is non-destructive evaluation of material. A time-domain, minimization approach is presented where exact gradients are computed using the adjoint problem. The approach is applied to a general form of Maxwell's equations including dispersive media and UPML. Successful reconstruction examples are presented both using synthetic and experimental measurement data. Parameter reduction of complex geometries using simplified models is an interesting topic that leads to an inverse problem. Gradients for subcell parameters are derived and a successful reconstruction example is presented for a combined dielectric sheet and slot geometry.

sted, utgiver, år, opplag, sider
Uppsala: Acta Universitatis Upsaliensis , 2005. , 47 s.
Serie
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 102
Emneord [en]
Maxwell's equations, time-domain, FDTD, finite-element, hybrid, thin sheet, waveguide, PML, inverse scattering, adjoint, gradient-based, minimization
HSV kategori
Forskningsprogram
Beräkningsvetenskap med inriktning mot numerisk analys
Identifikatorer
URN: urn:nbn:se:uu:diva-6013ISBN: 91-554-6364-9 (tryckt)OAI: oai:DiVA.org:uu-6013DiVA: diva2:167116
Disputas
2005-11-04, Room 2446, Polacksbacken, Lägerhyddsvägen 2D, Uppsala, 10:15 (engelsk)
Opponent
Veileder
Tilgjengelig fra: 2005-10-11 Laget: 2005-10-11 Sist oppdatert: 2011-10-27bibliografisk kontrollert
Delarbeid
1. Hybrid time domain solvers for the Maxwell equations in 2D
Åpne denne publikasjonen i ny fane eller vindu >>Hybrid time domain solvers for the Maxwell equations in 2D
Vise andre…
2002 (engelsk)Inngår i: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 53, 2185-2199 s.Artikkel i tidsskrift (Fagfellevurdert) Published
HSV kategori
Identifikatorer
urn:nbn:se:uu:diva-44333 (URN)10.1002/nme.380 (DOI)
Prosjekter
GEMS
Tilgjengelig fra: 2007-01-26 Laget: 2007-01-26 Sist oppdatert: 2014-09-03bibliografisk kontrollert
2. Waveguide Truncation Using UPML in the Finite-Element Time-Domain Method
Åpne denne publikasjonen i ny fane eller vindu >>Waveguide Truncation Using UPML in the Finite-Element Time-Domain Method
2005 (engelsk)Rapport (Annet vitenskapelig)
Serie
Technical report / Department of Information Technology, Uppsala University, ISSN 1404-3203 ; 2005-026
HSV kategori
Identifikatorer
urn:nbn:se:uu:diva-80256 (URN)
Prosjekter
GEMS
Tilgjengelig fra: 2007-02-03 Laget: 2007-02-03 Sist oppdatert: 2014-09-03bibliografisk kontrollert
3. Solving inverse electromagnetic problems using FDTD and gradient-based minimization
Åpne denne publikasjonen i ny fane eller vindu >>Solving inverse electromagnetic problems using FDTD and gradient-based minimization
2006 (engelsk)Inngår i: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 68, 650-673 s.Artikkel i tidsskrift (Fagfellevurdert) Published
HSV kategori
Identifikatorer
urn:nbn:se:uu:diva-80802 (URN)10.1002/nme.1731 (DOI)000241713800003 ()
Prosjekter
GEMS
Tilgjengelig fra: 2007-01-26 Laget: 2007-01-26 Sist oppdatert: 2011-11-29bibliografisk kontrollert
4. Thin Sheet Modeling Using Shell Elements in the Finite-Element Time-Domain Method
Åpne denne publikasjonen i ny fane eller vindu >>Thin Sheet Modeling Using Shell Elements in the Finite-Element Time-Domain Method
2006 (engelsk)Inngår i: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 54, 28-34 s.Artikkel i tidsskrift (Fagfellevurdert) Published
HSV kategori
Identifikatorer
urn:nbn:se:uu:diva-80325 (URN)10.1109/TAP.2005.861554 (DOI)000235016700004 ()
Prosjekter
GEMS
Tilgjengelig fra: 2007-01-26 Laget: 2007-01-26 Sist oppdatert: 2016-01-28bibliografisk kontrollert
5. Modeling of inhomogeneous waveguides using hybrid methods
Åpne denne publikasjonen i ny fane eller vindu >>Modeling of inhomogeneous waveguides using hybrid methods
2005 (engelsk)Manuskript (preprint) (Annet vitenskapelig)
HSV kategori
Identifikatorer
urn:nbn:se:uu:diva-93590 (URN)
Prosjekter
GEMS
Tilgjengelig fra: 2005-10-11 Laget: 2005-10-11 Sist oppdatert: 2011-11-10bibliografisk kontrollert

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