Negative capacitor paves the way to ultra-broadband metamaterials

Hrabar, Silvio; Krois, Igor; Bonic, Ivan; Kiricenko, Aleksandar

doi:10.1063/1.3671366

Cited by 102 publications

(109 citation statements)

References 15 publications

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“…Both aspects have to be treated with extreme caution. Recent experiments on metamaterials composed of active non-Foster elements operating at MHz and GHz frequencies [20,21] have shown rather constant superluminal electromagnetic phase and group velocities from 2 MHz to 40 MHz frequency [21] (more than four octaves bandwidth). The frequency dependence occurring at yet higher frequencies guarantees the fundamental consistency with causality and with the laws of special relativity [20,21].…”

Section: Resultsmentioning

confidence: 99%

Photorealistic ray tracing of free-space invisibility cloaks made of uniaxial dielectrics

Halimeh¹,

Wegener²

2012

Opt. Express

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Abstract:The design rules of transformation optics generally lead to spatially inhomogeneous and anisotropic impedance-matched magnetodielectric material distributions for, e.g., free-space invisibility cloaks. Recently, simplified anisotropic non-magnetic free-space cloaks made of a locally uniaxial dielectric material (calcite) have been realized experimentally. In a two-dimensional setting and for in-plane polarized light propagating in this plane, the cloaking performance can still be perfect for light rays. However, for general views in three dimensions, various imperfections are expected. In this paper, we study two different purely dielectric uniaxial cylindrical free-space cloaks. For one, the optic axis is along the radial direction, for the other one it is along the azimuthal direction. The azimuthal uniaxial cloak has not been suggested previously to the best of our knowledge. We visualize the cloaking performance of both by calculating photorealistic images rendered by ray tracing. Following and complementing our previous ray-tracing work, we use an equation of motion directly derived from Fermat's principle. The rendered images generally exhibit significant imperfections. This includes the obvious fact that cloaking does not work at all for horizontal or for ordinary linear polarization of light. Moreover, more subtle effects occur such as viewing-angle-dependent aberrations. However, we still find amazingly good cloaking performance for the purely dielectric azimuthal uniaxial cloak.

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Section: Resultsmentioning

confidence: 99%

Photorealistic ray tracing of free-space invisibility cloaks made of uniaxial dielectrics

Halimeh¹,

Wegener²

2012

Opt. Express

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“…On the other hand, considering the fact that the limited bandwidth of the detached ZIM lens arises from the highly dispersive constitutive parameters of bulky passive metamaterials, one can predict that the incorporation of active elements [35] or gain medium [36] into the metamaterial structure could enable broadband operation. In Ref.…”

Section: The Methods For Broadening the Bandwidth Of The Detached Zimlmentioning

confidence: 99%

“…In Ref. [35], S. Hrabar et al demonstrated how to overcome the dispersion constraints in metamaterials for radio frequencies with the help of active non-Foster negative capacitors. Their designed metamaterial exhibits almost dispersionless near-zero permittivity behavior over a very broad bandwidth of more than four octaves (2 MHz-40 MHz).…”

Section: The Methods For Broadening the Bandwidth Of The Detached Zimlmentioning

confidence: 99%

A Detached Zero Index Metamaterial Lens for Antenna Gain Enhancement

Meng¹,

Li²,

Zhang³

et al. 2012

PIER

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Abstract-In this paper, a detached zero index metamaterial lens (ZIML) consisting of metal strips and modified split ring resonators (MSRRs) is proposed for antenna gain enhancement. The effective permittivity and permeability of the detached ZIML are designed to synchronously approach zero, which leads the ZIML to having an effective wave impedance matching with air and near-zero index simultaneously. As a result, neither does the detached ZIML need to be embedded in horns aperture nor depends on auxiliary reflectors in enhancing antenna gain, which is quite different from conventional ZIMLs. Moreover, the distance between antenna and the detached ZIML slightly affect the gain enhancement, which further confirms that the ZIML can be detached from antennas. Simulated results show that the effective refractive index of the detached ZIML is near zero in a broad frequency range where the effective relative wave impedance is close to 1. The detached ZIML is fabricated and tested by placing it in front of an H-plane horn antenna. One finds that evident gain enhancement is obtained from 8.9 GHz to 10.8 GHz and the greatest gain enhancement reaches up to 4.02 dB. In addition, the detached ZIML can also work well at other frequencies by adjusting its geometric parameters to scale, which is demonstrated by designing and simulating two detached ZIMLs with center frequencies of 2.4 GHz and 5.8 GHz, respectively.

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“…Negative capacitor is actually a source that supplies additional current to the positive capacitor [8]. This additional current causes faster charging and therefore decreases the effective capacitance.…”

Section: Introductionmentioning

confidence: 99%

“…From the circuit theory point of view, one may say that the dispersion in passive metamaterials occurs due to the basic difference in the frequency behavior of a capacitor and an inductor. Very recently, it has been shown that, in some cases, it is possible to overcome basic dispersion constrains (1,2) by the use of electronic circuits that behave as negative capacitors or negative inductors (so-called non-Foster elements [5][6][7][8][9]). The simplest implementation (Fig.…”

Section: Introductionmentioning

confidence: 99%

Stability Analysis of Superluminal Metamaterial Transmission Line with Realistic Non-Foster Negative Capacitors

2012

Self Cite

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Original scientific paperRecently, it has been shown possible to go around basic dispersion energy constraints that limit bandwidth of every passive metamaterial and construct a broadband active Epsilon-Near-Zero superluminal transmission line. A basic building block of this unusual transmission line is an active 'tank circuit' that contains both conventional (positive) capacitor and non-Foster negative capacitor. Published theoretical studies revealed that such a 'tank circuit' is stable if an overall capacitance is positive. These studies assumed lossless host transmission line periodically loaded with ideal dispersionless negative capacitors. However, a possible influence of the imperfections of a realistic negative capacitor (its dispersion and loss/gain) on the stability has not been investigated so far. Here, stability analysis of realistic superluminal transmission line is performed in Laplace domain. The obtained results are in a good agreement with those obtained in recent experiments on active transmission line developed at University of Zagreb.Key words: Non-Foster Element, Negative Capacitor, Stability, Metamaterial, Superluminal Propagation Analiza stabilnosti superluminalne prijenosne linije temeljene na metamaterijalu s neidalnim neFosterovim negativnim kondenzatorima. Nedavno je pokazano da je moguće zaobići temeljne energetskodisperzijske uvjete koji ograničavaju širinu frekvencijskog pojasa svakog pasivnog metamaterijala. Takoîer je pokazano da je moguće konstruirati širokopojasnu aktivnu superluminalnu prijenosnu liniju s približno nultom permitivnosti (ENZ). Osnovni gradivni element ove neuobičajne linije je aktivni "titrajni krug" koji se sastoji od klasičnog (pozitivnog) i ne-Fosterovog negativnog kondenzatora. Do sada objavljene teorijske studije pokazale su da je ovakav "titrajni krug" stabilan ako je ekvivalentni ukupni kapacitet pozitivan. Meîutim, stvarni (neidalni) negativni kondenzator uvijek ima gubitke (ili pojačanje) i disperziju. Utjecaj ovih nesavršenosti na stabilnost superluminalne linije je nejasan i do sada nije istraživan. Stoga je u ovomečlanku načinjena analiza stabilnosti neidealne superluminalne prijenosne u Laplaceovoj domeni. Rezultati analize su u vrlo dobrom suglasju s nedavno objavljenim rezultatima mjerenja na aktivnoj superluminalnoj prijenosnoj liniji koja je razvijena na Sveučilištu u Zagrebu.

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Negative capacitor paves the way to ultra-broadband metamaterials

Cited by 102 publications

References 15 publications

Photorealistic ray tracing of free-space invisibility cloaks made of uniaxial dielectrics

Photorealistic ray tracing of free-space invisibility cloaks made of uniaxial dielectrics

A Detached Zero Index Metamaterial Lens for Antenna Gain Enhancement

Stability Analysis of Superluminal Metamaterial Transmission Line with Realistic Non-Foster Negative Capacitors

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