Physical limitations on broadband invisibility based on fast-light media

Abdelrahman, Mohamed Ismail; Hayran, Zeki; Chen, Aobo; Monticone, Francesco

doi:10.1038/s41467-021-22972-w

Cited by 7 publications

(2 citation statements)

References 18 publications

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“…Refs. 33 , 36 have also explored stability considerations in active scattering systems, pointing out related limitations. Overall, the theoretical proposal in Ref.…”

Section: Resultsmentioning

confidence: 99%

Stability bounds on superluminal propagation in active structures

et al. 2022

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Active materials have been explored in recent years to demonstrate superluminal group velocities over relatively broad bandwidths, implying a potential path towards bold claims such as information transport beyond the speed of light, as well as antennas and metamaterial cloaks operating over very broad bandwidths. However, causality requires that no portion of an impinging pulse can pass its precursor, implying a fundamental trade-off between bandwidth, velocity and propagation distance. Here, we clarify the general nature of superluminal propagation in active structures and derive a bound on these quantities fundamentally rooted into stability considerations. By applying filter theory, we show that this bound is generally applicable to causal structures of arbitrary complexity, as it applies to each zero-pole pair describing their response. As the system complexity grows, we find that only minor improvements in superluminal bandwidth can be practically achieved. Our results provide physical insights into the limitations of superluminal structures based on active media, implying severe constraints in several recently proposed applications.

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“…Refs. 33 , 36 have also explored stability considerations in active scattering systems, pointing out related limitations. Overall, the theoretical proposal in Ref.…”

Section: Resultsmentioning

confidence: 99%

Stability bounds on superluminal propagation in active structures

et al. 2022

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“…Indeed, several proposals utilizing active "non-Foster" elements have shown that the bandwidth of small antennas [50] and cloaking devices [51], [52], [53], [54] can be extended beyond what is possible with a passive system. However, active elements typically increase the noise level of the system [55] and can lead to potential instabilities (unbounded oscillations in time) [54], [56], [57], thereby disrupting the desired functionality.…”

Section: Impedance Matchingmentioning

confidence: 99%

Using Time-Varying Systems to Challenge Fundamental Limitations in Electromagnetics

Hayran¹,

Monticone²

2022

Preprint

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Time-varying components provide an exceptional opportunity to explore novel means for building efficient electromagnetic devices. While such explorations date back to more than half a century ago, recent years have experienced a renewed and increased interest into the design of dynamic electromagnetic systems. This resurgence has been partly fueled by the desire to surpass the performance of conventional devices, and to enable systems that can challenge various well-established physical bounds, such as the Bode-Fano limit, the Chu limit, etc. Here, we overview this emerging research area and provide a concise and systematic summary of the most relevant applications for which the relevant physical bounds can be overcome through time-varying elements. Besides leading to devices with superior performances, such research endeavors open new possibilities and might offer insight towards future all-electromagnetic/optical technologies.

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