Limits...
Temperature-frequency converter using a liquid crystal cell as a sensing element.

Marcos C, Sánchez Pena JM, Torres JC, Isidro Santos J - Sensors (Basel) (2012)

Bottom Line: The variation of the dielectric permittivity with temperature is used to modify the capacitance of a plain capacitor using a LC material as non-ideal dielectric.The output frequency is related to the temperature of LC cell through the equations associated to the oscillator circuit.The experimental results show excellent temperature sensitivity, with a variation of 0.40% of the initial frequency per degree Celsius in the temperature range from -6 °C to 110 °C.

View Article: PubMed Central - PubMed

Affiliation: Departamento de Tecnología Electrónica, Universidad Carlos III de Madrid, Madrid, Spain. cmarcos@ing.uc3m.es

ABSTRACT
A new temperature-frequency converter based on the variation of the dielectric permittivity of the Liquid Crystal (LC) material with temperature has been demonstrated. Unlike other temperature sensors based on liquid crystal processing optical signals for determining the temperature, this work presents a system that is able to sense temperature by using only electrical signals. The variation of the dielectric permittivity with temperature is used to modify the capacitance of a plain capacitor using a LC material as non-ideal dielectric. An electric oscillator with an output frequency depending on variable capacitance made of a twisted-nematic (TN) liquid crystal (LC) cell has been built. The output frequency is related to the temperature of LC cell through the equations associated to the oscillator circuit. The experimental results show excellent temperature sensitivity, with a variation of 0.40% of the initial frequency per degree Celsius in the temperature range from -6 °C to 110 °C.

Show MeSH
Variation of output frequency as a function of the temperature for different voltages applied to NLC cell.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3376606&req=5

f7-sensors-12-03204: Variation of output frequency as a function of the temperature for different voltages applied to NLC cell.

Mentions: The results obtained from the experimental setup are shown in Figure 7. Using the isothermal stage, the temperature was linearly increased from room temperature (20 °C) to nearly above the NLC clearing point. For this temperature range, different applied voltages to the NLC cell were tested in order to obtain the optimal value in terms of the sensitivity and linearity of the system. A starting frequency of 4.5 kHz was set at room temperature in all tests carried out. Results show the output signal frequency is a function of the temperature. As has been expected, as a consequence of parallel permittivity (ɛ//) highest dependence on temperature, the frequency variation is greater when higher average voltage is applied to the NLC cell. Figure 7 shows a sharp change of the curve slopes around a temperature of 100 °C. This is due to the NLC cell getting close to its clearing temperature.


Temperature-frequency converter using a liquid crystal cell as a sensing element.

Marcos C, Sánchez Pena JM, Torres JC, Isidro Santos J - Sensors (Basel) (2012)

Variation of output frequency as a function of the temperature for different voltages applied to NLC cell.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3376606&req=5

f7-sensors-12-03204: Variation of output frequency as a function of the temperature for different voltages applied to NLC cell.
Mentions: The results obtained from the experimental setup are shown in Figure 7. Using the isothermal stage, the temperature was linearly increased from room temperature (20 °C) to nearly above the NLC clearing point. For this temperature range, different applied voltages to the NLC cell were tested in order to obtain the optimal value in terms of the sensitivity and linearity of the system. A starting frequency of 4.5 kHz was set at room temperature in all tests carried out. Results show the output signal frequency is a function of the temperature. As has been expected, as a consequence of parallel permittivity (ɛ//) highest dependence on temperature, the frequency variation is greater when higher average voltage is applied to the NLC cell. Figure 7 shows a sharp change of the curve slopes around a temperature of 100 °C. This is due to the NLC cell getting close to its clearing temperature.

Bottom Line: The variation of the dielectric permittivity with temperature is used to modify the capacitance of a plain capacitor using a LC material as non-ideal dielectric.The output frequency is related to the temperature of LC cell through the equations associated to the oscillator circuit.The experimental results show excellent temperature sensitivity, with a variation of 0.40% of the initial frequency per degree Celsius in the temperature range from -6 °C to 110 °C.

View Article: PubMed Central - PubMed

Affiliation: Departamento de Tecnología Electrónica, Universidad Carlos III de Madrid, Madrid, Spain. cmarcos@ing.uc3m.es

ABSTRACT
A new temperature-frequency converter based on the variation of the dielectric permittivity of the Liquid Crystal (LC) material with temperature has been demonstrated. Unlike other temperature sensors based on liquid crystal processing optical signals for determining the temperature, this work presents a system that is able to sense temperature by using only electrical signals. The variation of the dielectric permittivity with temperature is used to modify the capacitance of a plain capacitor using a LC material as non-ideal dielectric. An electric oscillator with an output frequency depending on variable capacitance made of a twisted-nematic (TN) liquid crystal (LC) cell has been built. The output frequency is related to the temperature of LC cell through the equations associated to the oscillator circuit. The experimental results show excellent temperature sensitivity, with a variation of 0.40% of the initial frequency per degree Celsius in the temperature range from -6 °C to 110 °C.

Show MeSH