Transmission-Line Metamaterials, Bianisotropy, and Transmission-Line Bianisotropy

Joni Vehmas

    Research output: ThesisDoctoral ThesisCollection of Articles

    Abstract

    Electromagnetic metamaterials are artificial composite materials which possess exotic and advantageous properties not attainable with natural materials. This thesis covers two notable classes of metamaterials: transmission-line metamaterials and bianisotropic media. While metamaterials are most commonly realized as bulk media consisting of small resonant inclusions, transmission-line structures offer an alternative, low-dispersion and low-loss way for realizing them. Bianisotropic media, on the other hand, are typically bulk metamaterials in which the electric and magnetic responses are coupled in a unique way. This thesis not only studies these two topics individually but also brings together these two as of yet disconnected research areas. In the first part of the thesis, the application of transmission-line metamaterials for realizing practical microwave devices is discussed. An electromagnetic cloaking device based on transmission-line networks is designed and manufactured and its operation in a practical antenna blockage scenario is confirmed experimentally. Moreover, two antenna designs based on such a cloak are proposed and studied numerically and experimentally. The proposed antennas have the special property of operating as a cloak at a higher frequency while simultaneously working efficiently as an antenna at a lower one. A flat, inhomogeneous microwave lens design which uses a set of periodically loaded one-dimensional transmission lines for manipulating the wave phase is suggested and studied numerically and experimentally. Finally, two horn-like antennas based on skewed transmission-line networks are proposed. It is confirmed that integrating such a network into a horn antenna can significantly improve its directivity. In the second part, bianisotropic media (or to be precise, their constituent bianisotropic particles) are studied analytically and numerically in relation to the problem of eliminating electromagnetic scattering. It is shown that bianisotropy can provide additional functionality and flexibility for controlling scattering. Zero backward, zero forward or zero total scattering are all possible with specific particle designs though some solutions may require active elements. In the final part, a novel idea of realizing bianisotropic media using periodically loaded transmission lines is investigated. Specifically, two classes of bianisotropic media, omega media and moving media, are studied. It is shown that the omega coupling is related to the asymmetry of the loading circuit, while the moving medium coupling is related to the nonreciprocity of the circuit. Example unit cells of both cases are presented and studied analytically and experimentally. The results have implications not only to the design of transmission-line metamaterials but also to the theory of material parameter extraction and modeling physically moving magnetodielectric media in a laboratory environment.
    Translated title of the contributionSiirtojohtometamateriaalit, bianisotropia ja bianisotropia siirtojohdoissa
    Original languageEnglish
    QualificationDoctor's degree
    Awarding Institution
    • Aalto University
    Supervisors/Advisors
    • Tretiakov, Sergei, Supervising Professor
    • Alitalo, Pekka, Thesis Advisor
    Publisher
    Print ISBNs978-952-60-6527-4
    Electronic ISBNs978-952-60-6528-1
    Publication statusPublished - 2015
    MoE publication typeG5 Doctoral dissertation (article)

    Keywords

    • metamaterials
    • transmission lines
    • bianisotropy
    • cloaking
    • antennas
    • scattering

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