{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,10]],"date-time":"2026-03-10T23:03:47Z","timestamp":1773183827498,"version":"3.50.1"},"reference-count":46,"publisher":"MDPI AG","issue":"3","license":[{"start":{"date-parts":[[2022,1,22]],"date-time":"2022-01-22T00:00:00Z","timestamp":1642809600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100001871","name":"Funda\u00e7\u00e3o para a Ci\u00eancia e Tecnologia","doi-asserted-by":"publisher","award":["POCI-01-0145-FEDER-031220"],"award-info":[{"award-number":["POCI-01-0145-FEDER-031220"]}],"id":[{"id":"10.13039\/501100001871","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100001871","name":"Funda\u00e7\u00e3o para a Ci\u00eancia e Tecnologia","doi-asserted-by":"publisher","award":["CEECIND\/00471\/2017"],"award-info":[{"award-number":["CEECIND\/00471\/2017"]}],"id":[{"id":"10.13039\/501100001871","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Polymers"],"abstract":"<jats:p>Relative humidity (RH) monitorization is of extreme importance on scientific and industrial applications, and optical fiber sensors (OFS) may provide adequate solutions. Typically, these kinds of sensors depend on the usage of humidity responsive polymers, thus creating the need for the characterization of the optical and expansion properties of these materials. Four different polymers, namely poly(vinyl alcohol), poly(ethylene glycol), Hydromed\u2122 D4 and microbiology agar were characterized and tested using two types of optical sensors. First, optical fiber Fabry\u2013Perot (FP) tips were made, which allow the dynamical measurement of the polymers\u2019 response to RH variations, in particular of refractive index, film thickness, and critical deliquescence RH. Using both FP tips and Long-Period fiber gratings, the polymers were then tested as RH sensors, allowing a comparison between the different polymers and the different OFS. For the case of the FP sensors, the PEG tips displayed excellent sensitivity above 80%RH, outperforming the other polymers. In the case of LPFGs, the 10% (wt\/wt) PVA one displayed excellent sensitivity in a larger working range (60 to 100%RH), showing a valid alternative to lower RH environment sensing.<\/jats:p>","DOI":"10.3390\/polym14030439","type":"journal-article","created":{"date-parts":[[2022,1,23]],"date-time":"2022-01-23T20:34:40Z","timestamp":1642970080000},"page":"439","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":21,"title":["Analysis of the Relative Humidity Response of Hydrophilic Polymers for Optical Fiber Sensing"],"prefix":"10.3390","volume":"14","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-3952-2311","authenticated-orcid":false,"given":"Bernardo","family":"Dias","sequence":"first","affiliation":[{"name":"INESC TEC\u2014Institute for Systems and Computer Engineering, Technology and Science, and Faculty of Sciences, University of Porto, 4169-007 Porto, Portugal"},{"name":"Department of Physics and Astronomy, Faculty of Sciences, University of Porto, 4169-007 Porto, Portugal"}]},{"given":"Jo\u00e3o","family":"Carvalho","sequence":"additional","affiliation":[{"name":"INESC TEC\u2014Institute for Systems and Computer Engineering, Technology and Science, and Faculty of Sciences, University of Porto, 4169-007 Porto, Portugal"},{"name":"Department of Physics and Astronomy, Faculty of Sciences, University of Porto, 4169-007 Porto, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-1031-9261","authenticated-orcid":false,"given":"Jo\u00e3o P.","family":"Mendes","sequence":"additional","affiliation":[{"name":"INESC TEC\u2014Institute for Systems and Computer Engineering, Technology and Science, and Faculty of Sciences, University of Porto, 4169-007 Porto, Portugal"},{"name":"Chemistry Research Unit, Faculty of Sciences, University of Porto, 4169-007 Porto, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3810-5943","authenticated-orcid":false,"given":"Jos\u00e9 M. M. M.","family":"Almeida","sequence":"additional","affiliation":[{"name":"INESC TEC\u2014Institute for Systems and Computer Engineering, Technology and Science, and Faculty of Sciences, University of Porto, 4169-007 Porto, Portugal"},{"name":"Department of Physics, School of Science and Technology, University of Tr\u00e1s-os-Montes e Alto Douro, 5001-801 Vila Real, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6205-9479","authenticated-orcid":false,"given":"Lu\u00eds C. C.","family":"Coelho","sequence":"additional","affiliation":[{"name":"INESC TEC\u2014Institute for Systems and Computer Engineering, Technology and Science, and Faculty of Sciences, University of Porto, 4169-007 Porto, Portugal"},{"name":"Department of Physics and Astronomy, Faculty of Sciences, University of Porto, 4169-007 Porto, Portugal"}]}],"member":"1968","published-online":{"date-parts":[[2022,1,22]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"967","DOI":"10.1364\/OL.14.000967","article-title":"Fiber-optic sensor for humidity","volume":"14","author":"Mitschke","year":"1989","journal-title":"Opt. Lett."},{"key":"ref_2","doi-asserted-by":"crossref","unstructured":"Wang, B., Zhang, F., Pang, F., and Wang, T. (2011, January 13\u201316). An optical fiber humidity sensor based on optical absorption. Proceedings of the Asia Communications and Photonics Conference and Exhibition. 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