Dissertation in the field of Radio Science and Engineering, Joni Vehmas

The title of thesis is Transmission-Line Metamaterials, Bianisotropy, and Transmission-Line Bianisotropy

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 way for realizing them. Bianisotropic media, on the other hand, are 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. A novel electromagnetic cloaking device based on transmission-line networks is presented and its operation in a practical antenna blockage scenario is studied. Moreover it is shown how such a cloak with small modifications can act simultaneously as an antenna. 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. Finally, two horn-like, directive antennas based on skewed transmission-line networks are proposed and studied.

In the second part, bianisotropic media (or to be precise, their constituent bianisotropic particles) are studied in relation to the problem of eliminating electromagnetic scattering. It is shown that bianisotropy can provide additional flexibility for controlling scattering with possible applications in, e.g., design of sensors.

The final part of the thesis concerns the novel idea of realizing bianisotropic media using periodically loaded transmission lines. Specifically, two classes of bianisotropic media, omega media and moving media, are studied. By choosing the loading circuit correctly, the transmission-line structure can be shown to behave effectively as a bianisotropic medium. The results have implications not only to the design of artificial electromagnetic materials but also to the theory of material parameter extraction and modeling physically moving natural materials in a laboratory environment.

Opponent: Professor Ekaterina Shamonina, University of Oxford, United Kingdom

Supervisor: Professor Sergei Tretyakov, Aalto University School of Electrical Engineering, Department of Radio Science and Engineering

Contact information:
Joni Vehmas
p. 050 436 4787
joni.vehmas@aalto.fi