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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.

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Equivalent capacitance of the NLC cell used in the T-f converter.
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f5-sensors-12-03204: Equivalent capacitance of the NLC cell used in the T-f converter.

Mentions: The LC device was electrically characterized by using the experimental procedure described in [5] that is able to derive the capacitance value of the LC device as a function of the applied voltage. Figure 5 shows the experimental capacitance value obtained for the NLC cell applying different voltage levels at 5 kHz. As expected, due to the LC molecular orientation with the electrical field, the equivalent capacitance presents a high dependency on the applied voltage. The measured value of the capacitance ranges from 3 nF (when no voltage is applied and the molecules remain parallel to the substrates) to 6 nF (for applied voltages above 5 Vrms that keeps the molecules perpendicular to the substrates). However, the equivalent resistor parameter is almost constant with an experimental obtained value of 1.5 MΩ.


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)

Equivalent capacitance of the NLC cell used in the T-f converter.
© Copyright Policy
Related In: Results  -  Collection

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

f5-sensors-12-03204: Equivalent capacitance of the NLC cell used in the T-f converter.
Mentions: The LC device was electrically characterized by using the experimental procedure described in [5] that is able to derive the capacitance value of the LC device as a function of the applied voltage. Figure 5 shows the experimental capacitance value obtained for the NLC cell applying different voltage levels at 5 kHz. As expected, due to the LC molecular orientation with the electrical field, the equivalent capacitance presents a high dependency on the applied voltage. The measured value of the capacitance ranges from 3 nF (when no voltage is applied and the molecules remain parallel to the substrates) to 6 nF (for applied voltages above 5 Vrms that keeps the molecules perpendicular to the substrates). However, the equivalent resistor parameter is almost constant with an experimental obtained value of 1.5 MΩ.

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