Publications by Theodoros Koutserimpas

Dipole polarizability of time-varying particles

Romain Christophe Rémy Fleury, Theodoros Koutserimpas, Mohammad Sajjad Mirmoosa

Invariance under time translation (or stationarity) is probably one of the most important assumptions made when investigating electromagnetic phenomena. Breaking this assumption is expected to open up novel possibilities and result in exceeding conventiona ...

2022

Electromagnetic waves under nonstationary conditions, the connection with parity-time symmetry and studies on resonant systems

Theodoros Koutserimpas

In this thesis, the electromagnetic wave propagation is studied in nonstationary-medium scenarios. The electromagnetic fields under material time-modulation are shown to conserve their momentum but not their energy. The mathematical foundations and analysi ...

EPFL2021

From Polarizability to Effective Permittivity of Time-Varying Materials

Romain Christophe Rémy Fleury, Theodoros Koutserimpas, Mohammad Sajjad Mirmoosa

In this talk, we describe excitation of time-varying dipolar particles (time-modulated meta-atoms) by external time-varying fields from a nonstationary and causal perspective. For a time-harmonic excitation, we introduce a complex-valued function, called t ...

IEEE2020

Electromagnetic fields in a time-varying medium: Exceptional points and operator symmetries

Romain Christophe Rémy Fleury, Theodoros Koutserimpas

In this paper, 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-variat ...

2020

Coupled-mode theory for stationary and nonstationary resonant sound propagation

Romain Christophe Rémy Fleury, Theodoros Koutserimpas

In this paper, we present a complete analytical derivation of the equations used for stationary and nonstationary wave systems regarding resonant sound transmission and reflection described by the phenomenological coupled-mode theory. We calculate the prop ...

2019

Active acoustic resonators with reconfigurable resonance frequency, absorption, and bandwidth

Hervé Lissek, Etienne Thierry Jean-Luc Rivet, Romain Christophe Rémy Fleury, Theodoros Koutserimpas

Acoustic resonators play a key role in the development of subwavelength-sized technologies capable of interacting with airborne audible sound, from its emission and absorption to its manipulation and processing. Specifically, artificial acoustic media made ...

American Physical Society (APS)2019

Review and accuracy comparison of various permittivity-averaging schemes for material discontinuities in the two-dimensional FDFD method: implementation using efficient computer graphics techniques

Theodoros Koutserimpas

2018

Zero refractive index in time-Floquet acoustic metamaterials

Romain Christophe Rémy Fleury, Theodoros Koutserimpas

New scientific investigations of artificially structured materials and experiments have exhibit wave manipulation to the extreme. In particular, zero refractive index metamaterials have been on the front line of wave physics research for their unique wave ...

2018

Electromagnetic Waves in a Time Periodic Medium With Step-Varying Refractive Index

Romain Christophe Rémy Fleury, Theodoros Koutserimpas

We present an exact mathematical framework for electromagnetic wave propagation in periodically time-modulated media, in which the permittivity is homogenous and modulated in a step-varying fashion. By using Hill’s equation theory, we show that this proble ...

2018

Parametric amplification and bidirectional invisibility in PT-symmetric time-Floquet systems

Romain Christophe Rémy Fleury, Theodoros Koutserimpas

Parity-time (PT)-symmetric wave devices, which exploit balanced interactions between material gain and loss, exhibit extraordinary properties, including lasing and flux-conserving scattering processes. In a seemingly different research field, periodically ...

2018

Nonreciprocal Gain in Non-Hermitian Time-Floquet Systems

Romain Christophe Rémy Fleury, Theodoros Koutserimpas

We explore the unconventional wave scattering properties of non-Hermitian systems in which amplification or damping are induced by time-periodic modulation. These non-Hermitian time-Floquet systems are capable of nonreciprocal operations in the frequency d ...

2018