[Paper Review] Holding and amplifying electromagnetic waves with temporal non-Foster metastructures

Víctor Pacheco‐Peña, Yasaman Kiasat+3 more|arXiv (Cornell University)|Apr 7, 2023

Metamaterials and Metasurfaces Applications8 citations

TL;DR

The paper shows that rapid, positive-to-negative temporal modulation of permittivity in non-Foster metastructures can halt an electromagnetic wave and exponentially amplify its frozen field, with thawing resuming propagation at the original or a new frequency.

ABSTRACT

We introduce a mechanism that can both hold and amplify electromagnetic waves by rapidly changing the permittivity of the medium during the wave travel from a positive to a dispersionless (i.e. non-Foster) negative value and then back again. The underlying physics behind this phenomenon is theoretically explored by considering a plane wave in an unbounded medium. Interestingly, we show that a rapid positive-to-negative temporal change of ε(t) causes the propagation of the wave to stop (observed by a frozen phase in time) while the amplitude of the frozen field exponentially grows. Stepping the permittivity back to the original (or a new) positive value will cause the wave to thaw and resume propagation with the original (or the new) frequency, respectively. We numerically study the case of dipole radiation in such time-varying non-Foster structures. As a possible implementation, we propose a parallel plate waveguide platform loaded with time-dependent media emulating parallel lumped non-Foster negative capacitors. Such non-Foster time-varying structures may open new venues in controlling and manipulating wave-matter interaction.

Motivation & Objective

• Motivate and understand how temporal modulation of permittivity can control wave propagation in non-Foster media.
• Theoretically analyze a plane wave in a time-varying, dispersionless negative medium to reveal freezing and amplification phenomena.
• Explore numerical and practical implementation avenues for such time-variant metamaterials.
• Propose a feasible experimental platform to emulate time-varying non-Foster behavior in a waveguide.

Proposed method

• Develop a theoretical model of a plane wave in an unbounded medium with time-varying permittivity ε(t).
• Analyze the effect of a rapid positive-to-negative temporal change in ε(t) on wave propagation, showing freezing of phase and exponential growth of the frozen field.
• Describe the thawing process when ε(t) is restored to a positive value, leading to resume of propagation with the original or a new frequency.
• Perform numerical study of dipole radiation in time-varying non-Foster structures.
• Propose a parallel-plate waveguide platform loaded with time-dependent media to emulate parallel lumped non-Foster negative capacitors.

Experimental results

Research questions

• RQ1 Can rapid temporal modulation from positive to negative (dispersionless) permittivity halt an electromagnetic wave and amplify the frozen field?
• RQ2 How does restoring the permittivity to a positive value affect wave thawing and the resulting frequency?
• RQ3 What is the behavior of dipole radiation in such time-varying non-Foster media?
• RQ4 What practical platform can realize time-dependent non-Foster metamaterials for these effects?

Key findings

• A rapid positive-to-negative ε(t) change halts wave propagation (frozen phase) while the field amplitude grows exponentially.
• Thawing by returning ε(t) to positive (or altering it) resumes propagation with the original or a new frequency.
• Numerical results demonstrate dipole radiation behavior in time-varying non-Foster structures.
• A parallel-plate waveguide with time-dependent media is proposed as a feasible implementation to emulate non-Foster negative capacitors.
• The study suggests new ways to control and manipulate wave–matter interactions using temporal non-Foster metastructures.