{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,4,7]],"date-time":"2026-04-07T17:14:18Z","timestamp":1775582058978,"version":"3.50.1"},"reference-count":22,"publisher":"MDPI AG","issue":"11","license":[{"start":{"date-parts":[[2022,5,26]],"date-time":"2022-05-26T00:00:00Z","timestamp":1653523200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Strategic Priority Research Program of the Chinese Academy of Sciences","award":["XDA22020502"],"award-info":[{"award-number":["XDA22020502"]}]},{"name":"Strategic Priority Research Program of the Chinese Academy of Sciences","award":["2005DP173065-2021-03"],"award-info":[{"award-number":["2005DP173065-2021-03"]}]},{"name":"Strategic Priority Research Program of the Chinese Academy of Sciences","award":["2019YFB2006003"],"award-info":[{"award-number":["2019YFB2006003"]}]},{"name":"Key Laboratory of Environmental Optics and Technology","award":["XDA22020502"],"award-info":[{"award-number":["XDA22020502"]}]},{"name":"Key Laboratory of Environmental Optics and Technology","award":["2005DP173065-2021-03"],"award-info":[{"award-number":["2005DP173065-2021-03"]}]},{"name":"Key Laboratory of Environmental Optics and Technology","award":["2019YFB2006003"],"award-info":[{"award-number":["2019YFB2006003"]}]},{"name":"National Key Research and Development Project","award":["XDA22020502"],"award-info":[{"award-number":["XDA22020502"]}]},{"name":"National Key Research and Development Project","award":["2005DP173065-2021-03"],"award-info":[{"award-number":["2005DP173065-2021-03"]}]},{"name":"National Key Research and Development Project","award":["2019YFB2006003"],"award-info":[{"award-number":["2019YFB2006003"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>To achieve multi-gas measurements of quartz-enhanced photoacoustic spectroscopy (QEPAS) sensors under a frequency-division multiplexing mode with a narrow modulation frequency interval, we report a frequency-domain detection method. A CH4 absorption line at 1653.72 nm and a CO2 absorption line at 2004.02 nm were investigated in this experiment. A modulation frequency interval of as narrow as 0.6 Hz for CH4 and CO2 detection was achieved. Frequency-domain 2f signals were obtained with a resolution of 0.125 Hz using a real-time frequency analyzer. With the multiple linear regressions of the frequency-domain 2f signals of various gas mixtures, small deviations within 2.5% and good linear relationships for gas detection were observed under the frequency-division multiplexing mode. Detection limits of 0.6 ppm for CH4 and 2.9 ppm for CO2 were simultaneously obtained. With the 0.6-Hz interval, the amplitudes of QEPAS signals will increase substantially since the modulation frequencies are closer to the resonant frequency of a QTF. Furthermore, the frequency-domain detection method with a narrow interval can realize precise gas measurements of more species with more lasers operating under the frequency-division multiplexing mode. Additionally, this method, with a narrow interval of modulation frequencies, can also realize frequency-division multiplexing detection for QEPAS sensors under low pressure despite the ultra-narrow bandwidth of the QTF.<\/jats:p>","DOI":"10.3390\/s22114030","type":"journal-article","created":{"date-parts":[[2022,5,31]],"date-time":"2022-05-31T02:30:06Z","timestamp":1653964206000},"page":"4030","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":9,"title":["Frequency-Domain Detection for Frequency-Division Multiplexing QEPAS"],"prefix":"10.3390","volume":"22","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-1201-463X","authenticated-orcid":false,"given":"Xiang","family":"Chen","sequence":"first","affiliation":[{"name":"Jinlin Institute of Technology, Nanjing 211169, China"},{"name":"Hefei Institute of Physical Science, Chinese Academy of Sciences, Hefei 230031, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Hao","family":"Liu","sequence":"additional","affiliation":[{"name":"Hefei Institute of Physical Science, Chinese Academy of Sciences, Hefei 230031, China"},{"name":"University of Science and Technology of China, Hefei 230026, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Mai","family":"Hu","sequence":"additional","affiliation":[{"name":"Hefei Institute of Physical Science, Chinese Academy of Sciences, Hefei 230031, China"},{"name":"University of Science and Technology of China, Hefei 230026, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Lu","family":"Yao","sequence":"additional","affiliation":[{"name":"Hefei Institute of Physical Science, Chinese Academy of Sciences, Hefei 230031, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Zhenyu","family":"Xu","sequence":"additional","affiliation":[{"name":"Hefei Institute of Physical Science, Chinese Academy of Sciences, Hefei 230031, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Hao","family":"Deng","sequence":"additional","affiliation":[{"name":"Hefei Institute of Physical Science, Chinese Academy of Sciences, Hefei 230031, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Ruifeng","family":"Kan","sequence":"additional","affiliation":[{"name":"Hefei Institute of Physical Science, Chinese Academy of Sciences, Hefei 230031, China"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2022,5,26]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"55","DOI":"10.1364\/AO.415236","article-title":"QEPAS sensor in a butterfly package and its application","volume":"60","author":"Milde","year":"2021","journal-title":"Appl. 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