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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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(a) Multivibrator oscillator circuit. (b) Multivibrator circuit with NLC cell.
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f3-sensors-12-03204: (a) Multivibrator oscillator circuit. (b) Multivibrator circuit with NLC cell.

Mentions: The T-f converter is based on the multivibrator circuit shown in Figure 3(a). The multivibrator circuit is able to generate a square wave output signal, which switches between two symmetrical levels, the high level with a voltage of +Vo and the low level of −Vo. The output square wave is a 50% duty cycle signal, therefore the output signal maintains the high level during 50% of the period and the remaining time output level is low.


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)

(a) Multivibrator oscillator circuit. (b) Multivibrator circuit with NLC cell.
© Copyright Policy
Related In: Results  -  Collection

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

f3-sensors-12-03204: (a) Multivibrator oscillator circuit. (b) Multivibrator circuit with NLC cell.
Mentions: The T-f converter is based on the multivibrator circuit shown in Figure 3(a). The multivibrator circuit is able to generate a square wave output signal, which switches between two symmetrical levels, the high level with a voltage of +Vo and the low level of −Vo. The output square wave is a 50% duty cycle signal, therefore the output signal maintains the high level during 50% of the period and the remaining time output level is low.

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