Research Article GelatinUsedasaTransductorinanOpticalHygrometerBasedona Fabry-Perot Interferometer Sergio Calixto Centro De Investigaciones En Optica, Loma Del osque 115, Leon, Gto C.P. 37150, Mexico Correspondence should be addressed to Sergio Calixto; scalixto@cio.mx Received 22 September 2022; Revised 1 November 2022; Accepted 3 November 2022; Published 23 November 2022 Academic Editor: Zhigang Zang Copyright © 2022 Sergio Calixto. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Te quantities that are usually measured are time, pressure, temperature, and relative humidity to mention but a few. Te word humidity is used when we are dealing with water vapor which is a gas. Te instrument used to measure the humidity is the hygrometer that can be based on electronics, optics, mechanics, chemicals, and others. Te measurement of humidity shows its importance in applications such as food processing, meteorological, semiconductor, building and construction, medical, and automotivetomentionbutafew.Tispapershowstheadaptationofanopticalinterferometer,theFabry•Perot(F•P),tomeasure the relative humidity. Te transductors that have been probed are gelatin•thin flms that are inserted between the mirrors of the FP. When water molecules are absorbed (desorbed) by the gelatin flm, its refractive index and thickness change giving a movement of the rings in the interference pattern. Te calibration plot comprises the ring displacement as a function of the relative humidity. 1. Introduction Itisunderstoodthatthetermhumidityreferstothepresence of water in gaseous form. Relative humidity is defned [1] as the ratio of the amount of water vapor present in the at• mospheretothemaximumamounttheatmospherecanhold and is expressed as a percentage. To monitor humidity, several techniques have been employed. Tere are diferent sensors based on electronics [2](miniaturizedelectronicsensors),masschange(basedon the principle of resonant frequency), mechanical (using synthetic fbers and human hair), and optical (like chilled mirror hygrometer), for example. Electronic sensors [2] can be classifed by the transduction scheme that they use to convert water vapor concentration into an electrical signal: capacitive [3, 4], resistive (DC resistance or AC impedance) [3, 4], and advanced resistive (piezoresistive). Each sensor hasadvantagesanddisadvantagesyetnoneofthemcanfulfl the majority of the requirements; thus, each one is used in a diferent case. Te key component in the RH sensors is the transductor that interacts with the water molecules. Te ideal sensing flm material will have characteristics such as high sensitivity to water molecules, linear response from 0% to 100% RH, short response time, and long•term stability to mention but a few. Te optical RH sensors are the ones based on optical fbers[5]andonholographicdevices[6–8], forexample.Te fber optics sensors use the techniques such as direct spectroscopic, evanescent wave, in•fber grating, and in• terferometric methods. Regarding the holographic sensors, there is one that uses a refection hologram for visual in• dication of environmental humidity. Te material that is used to fabricate the hologram is a photopolymer. Once the hologram is made, white light is sent to it and the refected light is analyzed. If the atmosphere humidity surrounding the hologram changes, the refected light will change color. When the humidity returns to the original frst value, the color refected by the hologram will return to his original value. Tat means it is reversible. Te range of color change, reversibility, and the response time of the hologram have been studied in a controlled humidity environment. Ho• lograms with response times from few seconds to tens of minutes have been designed. Another sensor based on color changes is mentioned in reference [9]. Hindawi Advances in Materials Science and Engineering Volume 2022, Article ID 5709126, 8 pages https://doi.org/10.1155/2022/5709126