Electromagnetic Fields in a Time-Varying Medium: Exceptional Points and Operator Symmetries

In this article, we study the interactions of electromagnetic waves with a non-dispersive dynamic medium that is temporally dependent. Electromagnetic fields under material time-modulation conserve their momentum but not their energy. We assume a time-variation of permittivity, permeability, and con...

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Bibliographic Details
Published in:IEEE transactions on antennas and propagation 2020-09, Vol.68 (9), p.6717-6724
Main Authors: Koutserimpas, Theodoros T., Fleury, Romain
Format: Article
Language:English
Subjects:
Conductivity
Electromagnetic fields
Electromagnetic propagation
Electromagnetic radiation
Electromagnetic scattering
Electromagnetism
Energy conservation
exceptional point theory
Media
Parity
parity operator symmetry
Periodic variations
Permittivity
Time-domain analysis
time-reversal
time-varying systems
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Summary:In this article, we study the interactions of electromagnetic waves with a non-dispersive dynamic medium that is temporally dependent. Electromagnetic fields under material time-modulation conserve their momentum but not their energy. We assume a time-variation of permittivity, permeability, and conductivity, and derive the appropriate time-domain solutions based on the causality state at a past observation time. We formulate a time-transitioning state matrix and connect the unusual energy transitions of electromagnetic fields in time-varying media with the exceptional point theory. This state-matrix approach allows us to analyze further the electromagnetic waves in terms of parity and time-reversal symmetries and signify parity-time symmetric wave-states without the presence of a spatially symmetric distribution of gain and loss, or any inhomogeneities and material periodicity. This article provides a useful arsenal to study electromagnetic wave phenomena under time-varying media and points out novel physical insights connecting the resulting energy transitions and electromagnetic modes with exceptional point physics and operator symmetries.
ISSN:0018-926X
1558-2221
DOI:10.1109/TAP.2020.2996822