## The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc. | |

Dissertation for the degree of Doctor of Science in Technology to be presented
with due permission of the Department of Electrical and Communications Engineering
for public examination and debate in Auditorium S2 at
Helsinki University of Technology (Espoo, Finland) on the 22^{nd} of March, 2004,
at 12 o'clock noon.

Dissertation in PDF format (ISBN 951-22-6929-5) [5031 KB]

Dissertation is also available in print (ISBN 951-22-6928-7)

Modeling of interfaces and layers with the finite-difference time-domain method (FDTD) is considered in this thesis. New numerical models are developed and verified.

A surface impedance boundary condition relates the tangential electric and magnetic fields on an interface between two materials. The exact surface impedance uniquely defines the electromagnetic fields outside the material. The material structure is removed from the computational space. The resulting computational savings are huge in electrically large problems, like the modeling of coated targets in military applications.

Using the surface impedance techniques in numerical methods is extremely reasonable when the reflection of electromagnetic fields from materials is difficult to compute directly. For example, if the wavelength inside the material under investigation is very small compared to the wavelength outside the material, the straightforward discretization of the fields inside the material is not a clever approach. The surface impedance boundary conditions may be utilized in such situations.

In this thesis, a higher-order FDTD-model of interfaces with metals and semiconductors is developed and verified. As the most important new feature, the model takes arbitrary excitations into account in a general fashion using spatial derivatives on the interface. Novel techniques for modeling of dielectric layers on metal surfaces are also developed. Application of the surface impedance concept to derive analytical absorbing boundary conditions is also considered.

An alternative and original model for electrically thin dispersive layers is introduced. Unusual electromagnetic properties of dispersive layers are numerically studied in the frequency range, where the real parts of material parameters are negative.

Applications of the surface impedance concept to modeling of antennas with artificial electromagnetic materials are presented with numerical results for prototype devices.

**Keywords:**
FDTD, surface impedance boundary condition, dielectric layer,
surface impedance, absorbing boundary condition, metamaterial

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© 2004 Helsinki University of Technology

Last update 2011-05-26