{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,12]],"date-time":"2025-10-12T04:32:37Z","timestamp":1760243557687,"version":"build-2065373602"},"reference-count":17,"publisher":"MDPI AG","issue":"3","license":[{"start":{"date-parts":[[2012,3,7]],"date-time":"2012-03-07T00:00:00Z","timestamp":1331078400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/3.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>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 \u22126 \u00b0C to 110 \u00b0C.<\/jats:p>","DOI":"10.3390\/s120303204","type":"journal-article","created":{"date-parts":[[2012,3,7]],"date-time":"2012-03-07T12:43:39Z","timestamp":1331124219000},"page":"3204-3214","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":17,"title":["Temperature-Frequency Converter Using a Liquid Crystal Cell as a Sensing Element"],"prefix":"10.3390","volume":"12","author":[{"given":"Carlos","family":"Marcos","sequence":"first","affiliation":[{"name":"Grupo de Displays y Aplicaciones Fot\u00f3nicas, Departamento de Tecnolog\u00eda Electr\u00f3nica, Universidad Carlos III de Madrid, Avda. de la Universidad s\/n, E28911, Legan\u00e9s, Madrid, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5903-5967","authenticated-orcid":false,"given":"Jos\u00e9 M. S\u00e1nchez","family":"Pena","sequence":"additional","affiliation":[{"name":"Grupo de Displays y Aplicaciones Fot\u00f3nicas, Departamento de Tecnolog\u00eda Electr\u00f3nica, Universidad Carlos III de Madrid, Avda. de la Universidad s\/n, E28911, Legan\u00e9s, Madrid, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Juan C.","family":"Torres","sequence":"additional","affiliation":[{"name":"Grupo de Displays y Aplicaciones Fot\u00f3nicas, Departamento de Tecnolog\u00eda Electr\u00f3nica, Universidad Carlos III de Madrid, Avda. de la Universidad s\/n, E28911, Legan\u00e9s, Madrid, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Jos\u00e9 Isidro","family":"Santos","sequence":"additional","affiliation":[{"name":"Grupo de Displays y Aplicaciones Fot\u00f3nicas, Departamento de Tecnolog\u00eda Electr\u00f3nica, Universidad Carlos III de Madrid, Avda. de la Universidad s\/n, E28911, Legan\u00e9s, Madrid, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2012,3,7]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","unstructured":"Laudyn, U.A., Kwasny, M., and Karpierz, M.A. (2009, January 10\u201312). Light beam steering in chiral nematic liquid crystals. Angers, France.","DOI":"10.1109\/ICTONMW.2009.5385579"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"11292","DOI":"10.1364\/OE.14.011292","article-title":"Adaptive liquid crystal lens with large focal length tunability","volume":"14","author":"Ren","year":"2006","journal-title":"Opt. Express"},{"key":"ref_3","unstructured":"Muller, S., Scheele, P., Weil, C., Wittek, M., Hock, C., and Jakoby, R. (2004, January 6\u201311). Tunable passive phase shifter for microwave applications using highly anisotropic liquid crystals. Fort Worth, TX, USA."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"3564","DOI":"10.1143\/JJAP.47.3564","article-title":"Large microwave birefringence liquid-crystal characterization for phase-shifter applications","volume":"47","author":"Dubois","year":"2008","journal-title":"Jpn. J. Appl. Phys"},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"L221","DOI":"10.1143\/JJAP.46.L221","article-title":"Sinusoidal voltage-controlled oscillator based on a liquid crystal cell as variable capacitance","volume":"46","author":"Torres","year":"2007","journal-title":"J. Appl. Phys"},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"126101","DOI":"10.1063\/1.3666865","article-title":"Phase-locked loop with a voltage controlled oscillator based on a liquid crystal cell as variable capacitance","volume":"82","author":"Marcos","year":"2011","journal-title":"Rev. Sci. Instrum"},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"4887","DOI":"10.3390\/s100504887","article-title":"Solvent vapour detection with cholesteric liquid crystals-optical and mass-sensitive evaluation of the sensor mechanism","volume":"10","author":"Mujahid","year":"2010","journal-title":"Sensors"},{"key":"ref_8","doi-asserted-by":"crossref","unstructured":"Namkung, J., Lindquist, R., and Abu Abed, A. (2008, January 3\u20136). Application to shear force sensors by homeotropic liquid crystal (LC) orientation (non-reviewed). Huntsville, AL, USA.","DOI":"10.1109\/SECON.2008.4494260"},{"key":"ref_9","doi-asserted-by":"crossref","unstructured":"Hassanzadeh, A., and Lindquist, R.G. (2011, January 22\u201324). Single chip solution to capacitive liquid crystal chemical and biological sensor. San Antonio, TX, USA.","DOI":"10.1109\/SAS.2011.5739774"},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"2","DOI":"10.1109\/19.755041","article-title":"Development of fiber optic liquid crystal sensor for pressure measurement","volume":"48","author":"Wolinski","year":"1999","journal-title":"IEEE Trans. Instrum. Measur"},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"905","DOI":"10.1109\/LPT.2006.872279","article-title":"Electrooptic temperature sensor based on a Fabry-Perot resonator with a liquid crystal film","volume":"18","author":"Kim","year":"2006","journal-title":"IEEE Photon. Technol. Lett"},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"219","DOI":"10.1016\/0260-8774(94)00055-E","article-title":"Use of liquid crystals as temperature sensors in food processing research","volume":"26","author":"Balasubramaniam","year":"1995","journal-title":"J. Food Eng"},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"2691","DOI":"10.1063\/1.1781363","article-title":"Cholesteric liquid-crystal laser as an optic fiber-based temperature sensor","volume":"85","author":"Moreira","year":"2004","journal-title":"Appl. Phys. Lett"},{"key":"ref_14","first-page":"1","article-title":"Liquid crystals for electro-optic applications","volume":"7","author":"Nalwa","year":"2001","journal-title":"Handbook of Advanced Electronic and Photonic Materials and Devices, Ten-Volume Set"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"204","DOI":"10.1109\/TDEI.2006.1593418","article-title":"Electrical modeling of liquid crystal displays-LCDs","volume":"13","author":"Costa","year":"2006","journal-title":"IEEE Trans. Dielectr. Electr. Insulat"},{"key":"ref_16","unstructured":"LC-Tec Available online: http:\/\/www.lc-tec.com\/products\/general-purpose-optical-shutters__24\/ (access on 12 January 2012)."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"161","DOI":"10.1080\/10587259608034593","article-title":"Effect of strong electric fields on phase transitions in some liquid crystals","volume":"288","author":"Basappa","year":"1995","journal-title":"Mol. Cryst. Liquid Cryst"}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/12\/3\/3204\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T21:49:16Z","timestamp":1760219356000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/12\/3\/3204"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2012,3,7]]},"references-count":17,"journal-issue":{"issue":"3","published-online":{"date-parts":[[2012,3]]}},"alternative-id":["s120303204"],"URL":"https:\/\/doi.org\/10.3390\/s120303204","relation":{},"ISSN":["1424-8220"],"issn-type":[{"type":"electronic","value":"1424-8220"}],"subject":[],"published":{"date-parts":[[2012,3,7]]}}}