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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.


Transient study of the voltage-tunable metamaterial electromagnetic response for an applied rectangular voltage pulse of 7 V amplitude and 70 ms duration at two characteristic frequencies.890 GHz (metamaterial resonance) and 920 GHz (maximum figure of merit). (a) Transmittance and (b) effective metamaterial index. The inset in (a) shows the dynamics of the tilt angle calculated at the center of the LC layer.
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f9: Transient study of the voltage-tunable metamaterial electromagnetic response for an applied rectangular voltage pulse of 7 V amplitude and 70 ms duration at two characteristic frequencies.890 GHz (metamaterial resonance) and 920 GHz (maximum figure of merit). (a) Transmittance and (b) effective metamaterial index. The inset in (a) shows the dynamics of the tilt angle calculated at the center of the LC layer.

Mentions: In order to study the metamaterial’s temporal response and dynamics, a rectangular voltage pulse of 7 V is applied between 0 and 70 ms. The inset in Fig. 9(a) shows the evolution of the maximum tilt angle, calculated at the center of the LC layer. The rise time depends on the applied voltage and is faster than the fall time, which is described by the physics of an exponential elastic relaxation22. However, the collective response of the metamaterial’s EM properties shows faster dynamics, as evidenced in Fig. 9, where the transmittance and the MM effective index are calculated as a function of time, for two characteristic frequencies: the magnetic resonance frequency (890 GHz) and the frequency at which the figure of merit is maximized (920 GHz). In the first case, both maximum transmittance modulation and refractive index change is achieved, while in the second the index modulation comes with a small change in transmittance. Also to be remarked, the transition of the MM index in the second scenario is not monotonic and both higher and lower values, compared to that of the steady-state, are observed during LC switching. This can be understood by noting the corresponding spectra in Fig. 8, indicating that the LC-tuning of the proposed THz-MM is governed by rich dynamics, which may provide an extra degree of freedom in the engineering of their properties. For instance, in the example investigated in Fig. 9 at f = 920 GHz, it is observed that the target value of the effective index at t = 70 ms can be achieved at approximately 20 ms with the same transmittance modulation. Thus, by overdriving the device at 7 V, the switch-on speed of the device can be significantly enhanced.


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

Zografopoulos DC, Beccherelli R - Sci Rep (2015)

Transient study of the voltage-tunable metamaterial electromagnetic response for an applied rectangular voltage pulse of 7 V amplitude and 70 ms duration at two characteristic frequencies.890 GHz (metamaterial resonance) and 920 GHz (maximum figure of merit). (a) Transmittance and (b) effective metamaterial index. The inset in (a) shows the dynamics of the tilt angle calculated at the center of the LC layer.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f9: Transient study of the voltage-tunable metamaterial electromagnetic response for an applied rectangular voltage pulse of 7 V amplitude and 70 ms duration at two characteristic frequencies.890 GHz (metamaterial resonance) and 920 GHz (maximum figure of merit). (a) Transmittance and (b) effective metamaterial index. The inset in (a) shows the dynamics of the tilt angle calculated at the center of the LC layer.
Mentions: In order to study the metamaterial’s temporal response and dynamics, a rectangular voltage pulse of 7 V is applied between 0 and 70 ms. The inset in Fig. 9(a) shows the evolution of the maximum tilt angle, calculated at the center of the LC layer. The rise time depends on the applied voltage and is faster than the fall time, which is described by the physics of an exponential elastic relaxation22. However, the collective response of the metamaterial’s EM properties shows faster dynamics, as evidenced in Fig. 9, where the transmittance and the MM effective index are calculated as a function of time, for two characteristic frequencies: the magnetic resonance frequency (890 GHz) and the frequency at which the figure of merit is maximized (920 GHz). In the first case, both maximum transmittance modulation and refractive index change is achieved, while in the second the index modulation comes with a small change in transmittance. Also to be remarked, the transition of the MM index in the second scenario is not monotonic and both higher and lower values, compared to that of the steady-state, are observed during LC switching. This can be understood by noting the corresponding spectra in Fig. 8, indicating that the LC-tuning of the proposed THz-MM is governed by rich dynamics, which may provide an extra degree of freedom in the engineering of their properties. For instance, in the example investigated in Fig. 9 at f = 920 GHz, it is observed that the target value of the effective index at t = 70 ms can be achieved at approximately 20 ms with the same transmittance modulation. Thus, by overdriving the device at 7 V, the switch-on speed of the device can be significantly enhanced.

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.