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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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Structure and working principle of a homogeneously aligned nematic liquid crystal cell.
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f1-sensors-12-03204: Structure and working principle of a homogeneously aligned nematic liquid crystal cell.

Mentions: Basically, the structure of a LC cell consists of two parallel transparent plates or substrates with a conductive layer (electrode) in their inner surfaces. Inner surfaces are conditioned by a specific alignment process to achieve a homogenous molecular order of the LC material which is retained between the parallel plates. The nematic phase is one of the most widely used LC phase for a variety of electro-optic applications. The orientation of the molecules in a nematic phase substance can be altered by the application of an external electric field. In order to build practical devices, liquid crystals are sandwiched between two electrodes; therefore, the molecules tilt angle can be driven by an external electric field applied between both electrodes (Figure 1).


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)

Structure and working principle of a homogeneously aligned nematic liquid crystal cell.
© Copyright Policy
Related In: Results  -  Collection

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

f1-sensors-12-03204: Structure and working principle of a homogeneously aligned nematic liquid crystal cell.
Mentions: Basically, the structure of a LC cell consists of two parallel transparent plates or substrates with a conductive layer (electrode) in their inner surfaces. Inner surfaces are conditioned by a specific alignment process to achieve a homogenous molecular order of the LC material which is retained between the parallel plates. The nematic phase is one of the most widely used LC phase for a variety of electro-optic applications. The orientation of the molecules in a nematic phase substance can be altered by the application of an external electric field. In order to build practical devices, liquid crystals are sandwiched between two electrodes; therefore, the molecules tilt angle can be driven by an external electric field applied between both electrodes (Figure 1).

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