Defence of doctoral thesis in the field of Radio Engineering, M.Sc.(Tech.) Grigorii Ptitcyn
M.Sc.(Tech.) Grigorii Ptitcyn will defend the thesis "On Electromagnetics of Time-Modulated Structures" on 21 January 2022 at 16 (EET) in Aalto University School of Electrical Engineering, Department of Electronics and Nanoengineering.
Opponent: Prof. Nader Engheta, University of Pennsylvania, USA
Supervisor: Prof. Sergei Tretyakov, Aalto University School of Electrical Engineering, Department of Electronics and Nanoengineering
Thesis available for public display at: https://aaltodoc.aalto.fi/doc_public/eonly/riiputus/
Doctoral theses in the School of Electrical Engineering: https://aaltodoc.aalto.fi/handle/123456789/53
Time modulation means temporal variation of properties of a structure, imposed by some external force. Depending on the spatial dimensions it can be considered as modulation of single meta-atoms or of the effective medium parameters. In addition to that, modulation itself can be tuned in many different ways, such as the modulation speed, amplitude, pulse shape, and more.. Time-modulation unlocks an additional degree of freedom in electromagnetic systems that immensely increase the number of possibilities to control light. It enables novel approaches to overcome natural limitations and realize unconventional functionalities.
This dissertation considers structures that have different spatial dimensions and various temporal modulations. We start from fundamental differences between static and time-varying systems and discuss the validity of the instantaneous response assumption. The first part of the dissertation focuses on phenomena that can be studied under this assumption. We show how arbitrarily modulated reactive circuit elements can mimic non-Foster behavior or cancel reflections from a load. For arbitrarily modulated meta-atoms we introduce the instantaneous power balance equation that can be used to engineer the radiated fields. For periodically modulated structures we apply the Floquet theorem to explain the properties of time-modulated capacitors in electric circuits and in capacitive metasurfaces. Applying this analysis we introduce a novel approach for designing nonreciprocal structures, which is significantly easier to realize in practice.
The second part of the dissertation deals with dipole polarizability of a single meta-atom and a transition towards time-modulated media with dispersion. We carefully derive general equations that in principle can be used for solving scattering problems in any geometry.
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