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An example of narrowband superluminal propagation in typical system with anomalous dispersion (Lorentz dispersion model 14 with normalized central frequency ω 0 = 1 and a half-power bandwidth Δω = 0.1). (a) Real (solid-blue) and imaginary (dashed-red) part of a complex index of refraction. (b) The phase velocity (solid-blue) and the group velocity (dashed-red). (c) Typical transmission-line-based ENZ metamaterial implementation. Here, series distributed inductance L 1 assures dispersionless effective permeability, while the lossy double-resonant circuit (L 2, R, L, CΔx) assures Lorentzian permittivity behavior with a narrowband region with anomalous dispersion.
(a) The properties of fictitious lossless broadband system with simultaneous superluminal phase and group velocities. The index of refraction (solid-blue) and the phase and group velocities (dashed-red). (b) The implementation based on active transmission-line non-Foster ENZ metamaterial. 17
Measurements in frequency-domain, (a) experimental set-up, (b) extracted effective permittivity (real part: solid-blue, imaginary part: dashed-red), (c) extracted index of refraction (real part-solid-blue, imaginary part: dashed-red, the lossless approximation: dotted-black), (d) extracted phase velocity (dashed-red) and the group velocity (solid-blue).
Measurements in time-domain, (a) experimental set-up, (b) time-domain waveforms (input signal: dashed-black, output signal with ENZ off: dashed-blue, output signal with ENZ on: solid-red), (c) FFT spectra (input signal: dashed-black, output signal with ENZ off: dotted-blue, output signal with ENZ on: solid-red).
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