Time-Varying Reactive Elements for Extreme Accumulation of Electromagnetic Energy

Abstract

Accumulation of energy by reactive elements is limited by the amplitude of time-harmonic external sources. In the steady-state regime, all incident power is fully reflected back to the external source, and the stored energy does not increase in time, although the external source continuously supplies energy. Here we show that this limitation can be removed if the reactive element is varying in time, properly modulated by an additional active but lossless device. We show that such time-varying lossless loads of a transmission line or lossless metasurfaces can accumulate electromagnetic energy supplied by a timeharmonic source continuously in time without any theoretical limit. We analytically derive the required time dependence of the load reactance and show that it can, in principle, be realized as a series connection of mixers and filters. Furthermore, we prove that by properly designing time-varying LC circuits, one can arbitrarily engineer the time dependence of the electric current in the circuit fed by a given time-harmonic external source. As an example, we theoretically demonstrate a circuit with a linearly increasing electric current through the inductor. Calculating the energy delivered to the LC circuit and the energy released from it, we show that a modulated LC circuit can accumulate huge energy from both the time-harmonic external source and the modulating device. Finally, we discuss how this stored energy can be released in the form of a time-compressed pulse.

Uniform-velocity spacetime crystals

“…The three primed variables ω e , v ± j and j in (33) and (35) may be converted to their unprimed counterparts using respectively ω e = γω e (Eq. (26)), the equation for v ± j in (14), and the length contraction formula…”

“…Time crystals were first studied in the 1960s under the form of temporally modulated 1D structures, whose controlled instabilities led to parametric amplifiers [5,6] and whose asymmetric frequency transitions led to nonreciprocal devices [7,8]. Such time crystals have recently experienced a regain of interest [9][10][11], and more generally time-varying structures [12][13][14]. Moreover, the concept of spontaneous time crystals, which are time crystals produced by a nonperiodic stimulus, was introduced as a new state of matter in [15].…”

A Dynamically Modulated All‐Dielectric Metasurface Doublet for Directional Harmonic Generation and Manipulation in Transmission

“…This creates a new paradigm for designing dynamic metasurfaces with 2π phase span and uniform amplitude. Furthermore, time‐modulated metasurfaces give rise to several exotic space‐time scattering phenomena and can be envisioned for a variety of novel applications such as magnetless nonreciprocal components, Doppler cloaking and illusion, pulse shaping, extreme energy accumulation, and localization of light . Development of all‐dielectric time‐modulated metasurfaces is of particular interest as they can enable directional harmonic generation and manipulation in transmission mode by establishing a Huygens' operation regime, eliminating the bidirectionality of harmonics generated by time‐modulated metasurfaces with single isolated resonances.…”

Time-modulated meta-atoms

“…For example, in Ref. [37], it is shown that properly modulating inductive load, reflections from the load can be completely eliminated.…”