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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.


Tilt angle profile.(a) in the x-y plane and (b) in three x-z planes indicated by dashed lines in (a), for an applied voltage of 2 V. The liquid-crystal molecules switch in the volume between the metallic fishnet electrodes, with some fringe-field effects near their borders. The tilt angle profile across the main volume of the metamaterial is typical of Fréedericksz transition in nematic liquid-crystal cells.
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f7: Tilt angle profile.(a) in the x-y plane and (b) in three x-z planes indicated by dashed lines in (a), for an applied voltage of 2 V. The liquid-crystal molecules switch in the volume between the metallic fishnet electrodes, with some fringe-field effects near their borders. The tilt angle profile across the main volume of the metamaterial is typical of Fréedericksz transition in nematic liquid-crystal cells.

Mentions: The application of the low-frequency control voltage with a root-mean-square value V between the two fishnet electrodes leads to the reorientation of the LC molecules. In the area between the metallic patches and stripes, the electric field points perpendicularly and induces a torque to the LC molecules. When the electric field intensity surpasses a certain threshold, the LC molecules tilt in the x-z plane, tending to align with the applied field. This LC switching behaviour resembles strongly the Fréedericksz transition in LC cells, as evidenced in Fig. 7, which plots the LC tilt angle profiles for V = 2 V, where the tilt angle is defined as the angle of the nematic director with respect to the x-y plane. The MM structural parameters are chosen as in the case investigated in Fig. 2. It is observed that between the electrodes the tilt angle is almost constant at the x-y plane, apart from some edge effects at the borders of the fishnet metallic structure. In the region away from the metallic network, the driving field intensity is not sufficient to induce a reorientation of the LC molecules. Nevertheless, it is important to point out that the magnetic resonance shift, which is the key aspect of the investigated LC-THz-MM, depends on the LC refractive index only between the electrodes, since this is where the gap plasmon mode is confined. In the x-z planes the tilt angle assumes a typical profile across the LC cell between the electrodes, as shown in Fig. 7(b), that obtains the maximum value at the mid-plane of the LC cell and a fixed value equal to the pretilt at the LC-metal interfaces, owing to the hard anchoring conditions.


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

Zografopoulos DC, Beccherelli R - Sci Rep (2015)

Tilt angle profile.(a) in the x-y plane and (b) in three x-z planes indicated by dashed lines in (a), for an applied voltage of 2 V. The liquid-crystal molecules switch in the volume between the metallic fishnet electrodes, with some fringe-field effects near their borders. The tilt angle profile across the main volume of the metamaterial is typical of Fréedericksz transition in nematic liquid-crystal cells.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f7: Tilt angle profile.(a) in the x-y plane and (b) in three x-z planes indicated by dashed lines in (a), for an applied voltage of 2 V. The liquid-crystal molecules switch in the volume between the metallic fishnet electrodes, with some fringe-field effects near their borders. The tilt angle profile across the main volume of the metamaterial is typical of Fréedericksz transition in nematic liquid-crystal cells.
Mentions: The application of the low-frequency control voltage with a root-mean-square value V between the two fishnet electrodes leads to the reorientation of the LC molecules. In the area between the metallic patches and stripes, the electric field points perpendicularly and induces a torque to the LC molecules. When the electric field intensity surpasses a certain threshold, the LC molecules tilt in the x-z plane, tending to align with the applied field. This LC switching behaviour resembles strongly the Fréedericksz transition in LC cells, as evidenced in Fig. 7, which plots the LC tilt angle profiles for V = 2 V, where the tilt angle is defined as the angle of the nematic director with respect to the x-y plane. The MM structural parameters are chosen as in the case investigated in Fig. 2. It is observed that between the electrodes the tilt angle is almost constant at the x-y plane, apart from some edge effects at the borders of the fishnet metallic structure. In the region away from the metallic network, the driving field intensity is not sufficient to induce a reorientation of the LC molecules. Nevertheless, it is important to point out that the magnetic resonance shift, which is the key aspect of the investigated LC-THz-MM, depends on the LC refractive index only between the electrodes, since this is where the gap plasmon mode is confined. In the x-z planes the tilt angle assumes a typical profile across the LC cell between the electrodes, as shown in Fig. 7(b), that obtains the maximum value at the mid-plane of the LC cell and a fixed value equal to the pretilt at the LC-metal interfaces, owing to the hard anchoring conditions.

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.