temperature-frequency converter using a liquid crystal cell as a sensing element频率温度转换器使用液晶单元作为传感元件.pdf

Sensors 2012, 12, 3204-3214; doi:10.3390/s120303204 OPEN ACCESS sensors ISSN 1424-8220 /journal/sensors Article Temperature-Frequency Converter Using a Liquid Crystal Cell as a Sensing Element Carlos Marcos *, José M. Sánchez Pena, Juan C. Torres and José Isidro Santos Grupo de Displays y Aplicaciones Fotónicas, Departamento de Tecnología Electrónica, Universidad Carlos III de Madrid, Avda. de la Universidad s/n, E28911, Leganés, Madrid, Spain; E-Mails: jmpena@ing.uc3m.es (J.M.S.P.); jctzafra@ing.uc3m.es (J.C.T.); jsantos@ing.uc3m.es (J.I.S.) * Author to whom correspondence should be addressed; E-Mail: cmarcos@ing.uc3m.es; Tel.: +34-91-624-5964; Fax: +34-91-624-9430. Received: 1 February 2012; in revised form: 2 March 2012 / Accepted: 2 March 2012 / Published: 7 March 2012 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