Sammanfattning
This dissertation deals with physical bounds on scattering and absorption of acoustic and electromagnetic waves. A general dispersion relation or sum rule for the extinction cross section of such waves is derived from the holomorphic properties of the scattering amplitude in the forward direction. The derivation is based on the forward scattering theorem via certain Herglotz functions and their asymptotic expansions in the lowfrequency and highfrequency regimes. The result states that, for a given interacting target, there is only a limited amount of scattering and absorption available in the entire frequency range. The forward dispersion relation is shown to be valuable for a broad range of frequency domain problems involving acoustic and electromagnetic interaction with matter on a macroscopic scale. In the modeling of a metamaterial, i.e., an engineered composite material that gains its properties by its structure rather than its composition, it is demonstrated that for a narrow frequency band, such a material may possess extraordinary characteristics, but that tradeoffs are necessary to increase its usefulness over a larger bandwidth.
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The dispersion relation for electromagnetic waves is also
applied to a large class of causal and reciprocal antennas to establish a priori estimates on the input impedance, partial realized gain, and bandwidth of electrically small and wideband antennas. The results are compared to the classical antenna bounds based on eigenfunction expansions, and it is demonstrated that the estimates presented in this dissertation offer sharper inequalities, and, more importantly, a new understanding of antenna dynamics in terms of lowfrequency considerations.
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The dissertation consists of 11 scientific papers of which several have been published in peerreviewed international journals. Both experimental results and numerical illustrations are included. The General Introduction addresses closely related subjects in theoretical physics and classical dispersion theory, e.g., the origin of the KramersKronig relations, the mathematical foundations of Herglotz functions, the extinction paradox for scattering of waves and particles, and nonforward dispersion relations with application to the prediction of bistatic radar cross sections.
<br>
<br>
The dispersion relation for electromagnetic waves is also
applied to a large class of causal and reciprocal antennas to establish a priori estimates on the input impedance, partial realized gain, and bandwidth of electrically small and wideband antennas. The results are compared to the classical antenna bounds based on eigenfunction expansions, and it is demonstrated that the estimates presented in this dissertation offer sharper inequalities, and, more importantly, a new understanding of antenna dynamics in terms of lowfrequency considerations.
<br>
<br>
The dissertation consists of 11 scientific papers of which several have been published in peerreviewed international journals. Both experimental results and numerical illustrations are included. The General Introduction addresses closely related subjects in theoretical physics and classical dispersion theory, e.g., the origin of the KramersKronig relations, the mathematical foundations of Herglotz functions, the extinction paradox for scattering of waves and particles, and nonforward dispersion relations with application to the prediction of bistatic radar cross sections.
Originalspråk  engelska 

Kvalifikation  Doktor 
Tilldelande institution 

Handledare 

Tilldelningsdatum  2008 sep. 23 
Förlag  
ISBN (tryckt)  9789162875145 
Status  Published  2008 
Bibliografisk information
Defence detailsDate: 20080923
Time: 10:15
Place: Lecture hall E:1406, Ebuilding, Ole Römers väg 3, Faculty of Engineering, Lund University
External reviewer(s)
Name: Bohren, Craig F.
Title: Professor
Affiliation: Pennsylvania State University, United States

Ämnesklassifikation (UKÄ)
 Elektroteknik och elektronik