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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Grating Coupler for Surface Waves Based on Electrical Displacement Currents

Brescia, Jonathan R 01 January 2019 (has links)
Bound electromagnetic surface waves can be excited by free-space waves on a corrugated conduction surface. These electromagnetic surface waves, called surface plasmon polaritons (SPPs), are coupled to a plasma of free charges, which travel together with the wave. We investigated the effect of separating metal corrugations from the smooth metal ground plane with a thin dielectric layer and show that SPPs can be excited via displacement currents. However, the SPP excitation resonances broaden and disappear as the dielectric thickness approaches 1% of the wavelength.
2

Hybrid Computational Algorithms for the Problem of Scattering from Grating Structures

Alavikia, Babak January 2011 (has links)
Modeling of wave scattering from grating couplers has become increasingly important due to extensive recent research interest in the problem of plasmonic resonance. Computational algorithms which are specially used to model the problem of scattering from the grating surfaces suffer from several drawbacks such as accuracy, computational efficiency, and generality. To address the challenges of the previous methods, this work presents a novel hybrid Finite Element-Boundary Integral Method (FE-BIM) solution to the problem of scattering from grating surfaces consisting of finite or infinite array of two-dimensional cavities and holes in an infinite metallic walls covered with a stratified dielectric layer. To solve the scattering problem from finite number of cavities or holes engraved in a perfectly conducting screen (PEC), the solution region is divided into interior regions containing the cavities or holes and the region exterior to them. The finite element formulation is applied inside the interior region to derive a linear system of equations associated with nodal field values. Using two-boundary formulation, the surface integral equation employing free-space Green's function is then applied at \emph{only} the opening of the cavities or holes to truncate the computational domain and to connect the matrix subsystem generated from each cavity or hole. The hybrid FE-BIM method is extended to solve the scattering problem from an infinite array of cavities or holes in a PEC screen by deriving the quasi-periodic Green's function. In the scattering problem from an infinite array of cavities, the finite element formulation is first used inside a single cavity in the unit-cell. Next, the surface integral equation employing the quasi-periodic Green's function is applied at the opening of \emph{only} a single cavity as a boundary constraint to truncate the computational domain. Effect of the infinite array of cavities is incorporated into the system of the nodal equations by the quasi-periodic Green's function. Finally, the method based on the hybrid FE-BIM is developed to solve the scattering problem from grating surfaces covered with a stratified dielectric layer. In this method, the surface integral equation employing grounded dielectric slab Green's function is applied at the opening of the cavities or holes inside the dielectric coating to truncate the solution region efficiently. An accurate algorithm is presented to derive the grounded dielectric slab Green's function in spatial domain incorporating the effects of the surface-waves and leaky-waves excited and propagated inside the dielectric slab. Numerical examples of near and far field calculations for finite or infinite array of cavities or holes are presented to validate accuracy, versatility, and efficiency of the algorithm presented in this thesis.
3

Hybrid Computational Algorithms for the Problem of Scattering from Grating Structures

Alavikia, Babak January 2011 (has links)
Modeling of wave scattering from grating couplers has become increasingly important due to extensive recent research interest in the problem of plasmonic resonance. Computational algorithms which are specially used to model the problem of scattering from the grating surfaces suffer from several drawbacks such as accuracy, computational efficiency, and generality. To address the challenges of the previous methods, this work presents a novel hybrid Finite Element-Boundary Integral Method (FE-BIM) solution to the problem of scattering from grating surfaces consisting of finite or infinite array of two-dimensional cavities and holes in an infinite metallic walls covered with a stratified dielectric layer. To solve the scattering problem from finite number of cavities or holes engraved in a perfectly conducting screen (PEC), the solution region is divided into interior regions containing the cavities or holes and the region exterior to them. The finite element formulation is applied inside the interior region to derive a linear system of equations associated with nodal field values. Using two-boundary formulation, the surface integral equation employing free-space Green's function is then applied at \emph{only} the opening of the cavities or holes to truncate the computational domain and to connect the matrix subsystem generated from each cavity or hole. The hybrid FE-BIM method is extended to solve the scattering problem from an infinite array of cavities or holes in a PEC screen by deriving the quasi-periodic Green's function. In the scattering problem from an infinite array of cavities, the finite element formulation is first used inside a single cavity in the unit-cell. Next, the surface integral equation employing the quasi-periodic Green's function is applied at the opening of \emph{only} a single cavity as a boundary constraint to truncate the computational domain. Effect of the infinite array of cavities is incorporated into the system of the nodal equations by the quasi-periodic Green's function. Finally, the method based on the hybrid FE-BIM is developed to solve the scattering problem from grating surfaces covered with a stratified dielectric layer. In this method, the surface integral equation employing grounded dielectric slab Green's function is applied at the opening of the cavities or holes inside the dielectric coating to truncate the solution region efficiently. An accurate algorithm is presented to derive the grounded dielectric slab Green's function in spatial domain incorporating the effects of the surface-waves and leaky-waves excited and propagated inside the dielectric slab. Numerical examples of near and far field calculations for finite or infinite array of cavities or holes are presented to validate accuracy, versatility, and efficiency of the algorithm presented in this thesis.
4

Laserstrukturierung von Mikroprägewerkzeugen und Abformung beugungsoptisch wirksamer Gitterstrukturen

Engel, Andy 28 July 2020 (has links)
In dieser Arbeit werden Ergebnisse der Untersuchungen zur Laserstrukturierung von Prägewerkezeugen sowie zur Abformung von Gitterstrukturen mit Gitterperioden von kleiner gleich 2 µm in verschiedene Folien und Werkstoffverbunde präsentiert und diskutiert. Die hierfür entwickelte Kombination von Laserprozessen wird erläutert. Des Weiteren sind die auf Basis der experimentellen Untersuchungen ermittelten Parameterräume aufgezeigt und in Bezug zu theoretischen Beschreibungsmodellen gesetzt. Limitationen und Potentiale der einzelnen Teilprozesse werden dargelegt. Unter Anwendung der beschriebenen Strukturierungs- und Prozessparameter ist die Erstellung funktional einsetzbarer Prägewerkzeuge möglich. Für die Strukturübertragung konnte die Abformbarkeit der in die Oberflächen der Prägewerkzeuge eingebrachten beugungsoptisch wirksamen Gitterstrukturen mit Gitterperioden von kleiner gleich 2 µm bei Kontaktzeiten im Millisekundenbereich nachgewiesen werden.

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