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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.


(a) Transmittance of the LC-THz metamaterial for various values of applied voltage. The limiting cases of resting and fully switched LC molecules are shown in dashed lines. The inset shows the corresponding absorption spectra, indicating a shift of the metamaterial resonance for increasing voltage values. (b) Effective metamaterial index for the cases studied in (a). In the range approximately between 0.9 and 1 THz, tuning from positive to zero to negative values is possible. The inset shows the maximum and average LC tilt angle. Owing to the hard anchoring conditions at the metallic surfaces, the resonance tuning effect saturates before the maximum tuning range is achieved.
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f8: (a) Transmittance of the LC-THz metamaterial for various values of applied voltage. The limiting cases of resting and fully switched LC molecules are shown in dashed lines. The inset shows the corresponding absorption spectra, indicating a shift of the metamaterial resonance for increasing voltage values. (b) Effective metamaterial index for the cases studied in (a). In the range approximately between 0.9 and 1 THz, tuning from positive to zero to negative values is possible. The inset shows the maximum and average LC tilt angle. Owing to the hard anchoring conditions at the metallic surfaces, the resonance tuning effect saturates before the maximum tuning range is achieved.

Mentions: The tuning of the metamaterial’s properties as a function of the applied voltage is investigated in Fig. 8. As the voltage is increased, the LC molecules are further tilted, the LC index along the z−axis moves from no towards the higher extraordinary value ne and induces a progressive shift of the magnetic resonance towards lower frequencies, as demonstrated in the inset of Fig. 8(a). The EM response to the applied voltage is non-linear and the tuning efficiency saturates as higher voltages are applied. This is a typical characteristic of LC-tunable devices, owing mainly to the strong boundary conditions, which force the LC molecules to stay anchored at the cell’s surfaces, thus hindering the overall average switching of the LC molecules. This can be observed in the inset of Fig. 8(b), where the maximum and average LC tilt angle are calculated in the x-y plane at z = 0 and −Ls/2 ≤ z ≤ Ls/2, respectively. Nevertheless, Fig. 8 demonstrates that a moderate voltage of 7 V is sufficient to cover more than 80% of the full tunability range corresponding to the two limit cases, which translates in a shift of more than 150 GHz. Therefore, extensive tunability is achieved for rather low applied voltage values, a fact that is very important in terms of switching power consumption. The latter can be approximated as P = CV2f, where f is the LC driving frequency, and C the capacitance of the LC cell. Assuming a total MM area of 3 × 3 mm2 (20 × 20 unit cells) and for the fully switched case, the capacitance is below 1 nF and the overall power consumption obtains very low values, below 100 μW.


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

Zografopoulos DC, Beccherelli R - Sci Rep (2015)

(a) Transmittance of the LC-THz metamaterial for various values of applied voltage. The limiting cases of resting and fully switched LC molecules are shown in dashed lines. The inset shows the corresponding absorption spectra, indicating a shift of the metamaterial resonance for increasing voltage values. (b) Effective metamaterial index for the cases studied in (a). In the range approximately between 0.9 and 1 THz, tuning from positive to zero to negative values is possible. The inset shows the maximum and average LC tilt angle. Owing to the hard anchoring conditions at the metallic surfaces, the resonance tuning effect saturates before the maximum tuning range is achieved.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f8: (a) Transmittance of the LC-THz metamaterial for various values of applied voltage. The limiting cases of resting and fully switched LC molecules are shown in dashed lines. The inset shows the corresponding absorption spectra, indicating a shift of the metamaterial resonance for increasing voltage values. (b) Effective metamaterial index for the cases studied in (a). In the range approximately between 0.9 and 1 THz, tuning from positive to zero to negative values is possible. The inset shows the maximum and average LC tilt angle. Owing to the hard anchoring conditions at the metallic surfaces, the resonance tuning effect saturates before the maximum tuning range is achieved.
Mentions: The tuning of the metamaterial’s properties as a function of the applied voltage is investigated in Fig. 8. As the voltage is increased, the LC molecules are further tilted, the LC index along the z−axis moves from no towards the higher extraordinary value ne and induces a progressive shift of the magnetic resonance towards lower frequencies, as demonstrated in the inset of Fig. 8(a). The EM response to the applied voltage is non-linear and the tuning efficiency saturates as higher voltages are applied. This is a typical characteristic of LC-tunable devices, owing mainly to the strong boundary conditions, which force the LC molecules to stay anchored at the cell’s surfaces, thus hindering the overall average switching of the LC molecules. This can be observed in the inset of Fig. 8(b), where the maximum and average LC tilt angle are calculated in the x-y plane at z = 0 and −Ls/2 ≤ z ≤ Ls/2, respectively. Nevertheless, Fig. 8 demonstrates that a moderate voltage of 7 V is sufficient to cover more than 80% of the full tunability range corresponding to the two limit cases, which translates in a shift of more than 150 GHz. Therefore, extensive tunability is achieved for rather low applied voltage values, a fact that is very important in terms of switching power consumption. The latter can be approximated as P = CV2f, where f is the LC driving frequency, and C the capacitance of the LC cell. Assuming a total MM area of 3 × 3 mm2 (20 × 20 unit cells) and for the fully switched case, the capacitance is below 1 nF and the overall power consumption obtains very low values, below 100 μW.

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.