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Tunable terahertz fishnet metamaterials based on thin nematic liquid crystal layers for fast switching.

Zografopoulos DC, Beccherelli R - Sci Rep (2015)

Bottom Line: A shift higher than 150 GHz is predicted for common dielectric and liquid crystalline materials used in terahertz technology and for low applied voltage values.Owing to the few micron-thick liquid crystal cell, the response speed of the tunable metamaterial is calculated as orders of magnitude faster than in demonstrated liquid-crystal based non-resonant terahertz components.Such tunable metamaterial elements are proposed for the advanced control of electromagnetic wave propagation in terahertz applications.

View Article: PubMed Central - PubMed

Affiliation: Consiglio Nazionale delle Ricerche, Istituto per la Microelettronica e Microsistemi (CNR-IMM), Roma 00133, Italy.

ABSTRACT
The electrically tunable properties of liquid-crystal fishnet metamaterials are theoretically investigated in the terahertz spectrum. A nematic liquid crystal layer is introduced between two fishnet metallic structures, forming a voltage-controlled metamaterial cavity. Tuning of the nematic molecular orientation is shown to shift the magnetic resonance frequency of the metamaterial and its overall electromagnetic response. A shift higher than 150 GHz is predicted for common dielectric and liquid crystalline materials used in terahertz technology and for low applied voltage values. Owing to the few micron-thick liquid crystal cell, the response speed of the tunable metamaterial is calculated as orders of magnitude faster than in demonstrated liquid-crystal based non-resonant terahertz components. Such tunable metamaterial elements are proposed for the advanced control of electromagnetic wave propagation in terahertz applications.

No MeSH data available.


Effective parameters of the LC-THz metamaterial under study (W = 110 μm and w = 40 μm) for the two extreme cases of LC molecular orientation, i.e. along the x− (rest case) and the z−axis (fully switched alignment).
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f4: Effective parameters of the LC-THz metamaterial under study (W = 110 μm and w = 40 μm) for the two extreme cases of LC molecular orientation, i.e. along the x− (rest case) and the z−axis (fully switched alignment).

Mentions: In parallel, the stripes connecting the metallic patches lead to an effective permittivity response of the metamaterial, whose cross-over frequency fco, i.e. where εeff = 0, can be adjusted by varying w. A negative MM index is possible, when both the permittivity and permeability values of the MM become negative. For the case of normal incidence, these are calculated in Fig. 4, following the procedure described in Ref. 48, and starting from the calculated transmission and reflection coefficients for a MM thickness dMM = Ls. The permeability spectra of Fig. 4(c) confirm the tuning of the magnetic resonance, and correspond to the same shift observed in the absorption peaks of Fig. 2. On the contrary, the effective MM permittivity does not depend significantly on the LC dielectric slab index (Fig. 4(b)), and thus by shifting the magnetic resonance from f > fco to f < fco the sign of the MM index nMM is reversed, as shown in Fig. 4(a). The peak of the high transmission windows in Fig. 2 coincides with the frequency where nMM ≃ np, indicating impedance matching. In the fully switched case nMM is negative in the interval 0.81 < f < 0.97 THz, while at 0.92 THz the figure of merit, defined as −Re{neff}/Im{eff}, is maximized.


Tunable terahertz fishnet metamaterials based on thin nematic liquid crystal layers for fast switching.

Zografopoulos DC, Beccherelli R - Sci Rep (2015)

Effective parameters of the LC-THz metamaterial under study (W = 110 μm and w = 40 μm) for the two extreme cases of LC molecular orientation, i.e. along the x− (rest case) and the z−axis (fully switched alignment).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4536660&req=5

f4: Effective parameters of the LC-THz metamaterial under study (W = 110 μm and w = 40 μm) for the two extreme cases of LC molecular orientation, i.e. along the x− (rest case) and the z−axis (fully switched alignment).
Mentions: In parallel, the stripes connecting the metallic patches lead to an effective permittivity response of the metamaterial, whose cross-over frequency fco, i.e. where εeff = 0, can be adjusted by varying w. A negative MM index is possible, when both the permittivity and permeability values of the MM become negative. For the case of normal incidence, these are calculated in Fig. 4, following the procedure described in Ref. 48, and starting from the calculated transmission and reflection coefficients for a MM thickness dMM = Ls. The permeability spectra of Fig. 4(c) confirm the tuning of the magnetic resonance, and correspond to the same shift observed in the absorption peaks of Fig. 2. On the contrary, the effective MM permittivity does not depend significantly on the LC dielectric slab index (Fig. 4(b)), and thus by shifting the magnetic resonance from f > fco to f < fco the sign of the MM index nMM is reversed, as shown in Fig. 4(a). The peak of the high transmission windows in Fig. 2 coincides with the frequency where nMM ≃ np, indicating impedance matching. In the fully switched case nMM is negative in the interval 0.81 < f < 0.97 THz, while at 0.92 THz the figure of merit, defined as −Re{neff}/Im{eff}, is maximized.

Bottom Line: A shift higher than 150 GHz is predicted for common dielectric and liquid crystalline materials used in terahertz technology and for low applied voltage values.Owing to the few micron-thick liquid crystal cell, the response speed of the tunable metamaterial is calculated as orders of magnitude faster than in demonstrated liquid-crystal based non-resonant terahertz components.Such tunable metamaterial elements are proposed for the advanced control of electromagnetic wave propagation in terahertz applications.

View Article: PubMed Central - PubMed

Affiliation: Consiglio Nazionale delle Ricerche, Istituto per la Microelettronica e Microsistemi (CNR-IMM), Roma 00133, Italy.

ABSTRACT
The electrically tunable properties of liquid-crystal fishnet metamaterials are theoretically investigated in the terahertz spectrum. A nematic liquid crystal layer is introduced between two fishnet metallic structures, forming a voltage-controlled metamaterial cavity. Tuning of the nematic molecular orientation is shown to shift the magnetic resonance frequency of the metamaterial and its overall electromagnetic response. A shift higher than 150 GHz is predicted for common dielectric and liquid crystalline materials used in terahertz technology and for low applied voltage values. Owing to the few micron-thick liquid crystal cell, the response speed of the tunable metamaterial is calculated as orders of magnitude faster than in demonstrated liquid-crystal based non-resonant terahertz components. Such tunable metamaterial elements are proposed for the advanced control of electromagnetic wave propagation in terahertz applications.

No MeSH data available.