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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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Output frequency variation as a function of temperature for an NLC cell (applied voltage of 6 Vrms).
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f8-sensors-12-03204: Output frequency variation as a function of temperature for an NLC cell (applied voltage of 6 Vrms).

Mentions: From the experimental results, the optimum value chosen for the applied voltage to the LC cell is 6 Vrms due to a better linearity compared to other values. Once this voltage is fixed, the temperature range has been extended to check the operating limits of the implemented system. Figure 8 shows the output signal frequency of the oscillator circuit as a function of temperature. The measurements were experimentally obtained in the temperature range from −20 °C to 130 °C. The sensor response can be linearly fit in the temperature range from 0 to 80 °C with a sensitivity of 14.37 Hz/°C (Figure 9(a)).


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)

Output frequency variation as a function of temperature for an NLC cell (applied voltage of 6 Vrms).
© Copyright Policy
Related In: Results  -  Collection

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

f8-sensors-12-03204: Output frequency variation as a function of temperature for an NLC cell (applied voltage of 6 Vrms).
Mentions: From the experimental results, the optimum value chosen for the applied voltage to the LC cell is 6 Vrms due to a better linearity compared to other values. Once this voltage is fixed, the temperature range has been extended to check the operating limits of the implemented system. Figure 8 shows the output signal frequency of the oscillator circuit as a function of temperature. The measurements were experimentally obtained in the temperature range from −20 °C to 130 °C. The sensor response can be linearly fit in the temperature range from 0 to 80 °C with a sensitivity of 14.37 Hz/°C (Figure 9(a)).

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