Measurement of Fibre Humidity Using Spectroscopic Method

Sensors, 2017

A wide range of applications such as health, human comfort, agriculture, food processing and storage, and electronic manufacturing, among others, require fast and accurate measurement of humidity. Sensors based on optical fibers present several advantages over electronic sensors and great research efforts have been made in recent years in this field. The present paper reports the current trends of optical fiber humidity sensors. The evolution of optical structures developed towards humidity sensing, as well as the novel materials used for this purpose, will be analyzed. Well-known optical structures, such as long-period fiber gratings or fiber Bragg gratings, are still being studied towards an enhancement of their sensitivity. Sensors based on lossy mode resonances constitute a platform that combines high sensitivity with low complexity, both in terms of their fabrication process and the equipment required. Novel structures, such as resonators, are being studied in order to improve the resolution of humidity sensors. Moreover, recent research on polymer optical fibers suggests that the sensitivity of this kind of sensor has not yet reached its limit. Therefore, there is still room for improvement in terms of sensitivity and resolution.

Fourier transform infrared – attenuated total reflectance (FTIR-ATR) spectroscopy was applied to trace changes in chemical fiber properties during the production process of insulating fiber mats. In combination with cluster analysis, FTIR spectra were used to interpret the homogeneity of the products. Beech wood (Fagus sylvatica L.) was used as a novel sustainable material for fiberboard production. The insulating fiberboards were either processed without binder or with potato pulp or potato starch as renewable binders and dried in a dryer or a microwave. FTIR spectral analyses revealed chemical modifications at the O-H association band of carbohydrates that distinguished the two different drying methods. Additions of plant-based renewable binders diminished the absorbance of the resulting products at characteristic wavenumbers in the IR. These decreases were closely correlated with the amount of added binder and thus have the potential to quantify binder additions to the fiberboards. Cluster analysis grouped FTIR spectra of samples from different production steps or processes correctly and therefore is an effective and simple technique for quality control of insulating fiberboards from renewable resources.

An optical fiber humidity sensor was fabricated using a hydrophilic gel (agarose) deposited on the tapered plastic optical fiber (POF). The sensing element, agarose, can absorb and exude moisture from/to the ambience, thereby altering its refractive index and changing its ability to modulate the intensity of light that propagates through the fiber. Thus, the operating principle of the sensor is based on the intensity modulation technique, which utilizes a tapered POF probe coated with agarose that is sensitive to humidity. The POF, which was fabricated using an etching method, has a waist diameter of 0.45 mm and tapering length of 10 mm. As the relative humidity varies from 50% to 80%, the output voltage of the sensor with agarose gel of 0.5% weight content decreases linearly from 2.24 mV to 1.55 mV. The agarose-based sensor produces a sensitivity of 0.0228 mV/%, with a slope linearity of more than 98.36%. The tapered fiber with agarose gel of 1% weight content produces a sensitivity of 0.0103 mV/% with a slope linearity of more than 94.95% and a limit of detection of 2.635%, while the tapered fiber with agarose gel of 1.5% weight content produces a sensitivity of 0.0079 mV/% with a slope linearity of more than 98.53% and a limit of detection of 6.853%. The fiber with agarose gel of 0.5% weight content shows higher sensitivity compared to that of 1% and 1.5% due to the effect of pore size, which changes with concentration. The results demonstrate that agarose-based optical fiber sensors are both sensitive and efficient for economical and flexible measurements of humidity.

2007

Un ni iv ve er rs si it tá á d di i B Br re es sc ci ia a, , I It ta aly Abstract: A comparative study of two biopolymer based fiber optic humidity sensors is presented in this paper. Sensing elements Agarose and Chitosan swells in the presence of water vapour and undergoes changes in refractive index and modulates the intensity of light propagating through a fiber with Agarose or Chitosan as cladding.

Photonics Letters of Poland, 2020

The article presents an inexpensive and simple method of fiber optic interference relative humidity (RH) sensors based on silk fibroin (SF) films. The sensors were made on standard multimode telecommunications optical fibers using dip-coating method and examined using broadband light sources. The measuring stand at which the basic sensor parameters were measured and the measured parameters were presented. Full Text: PDF ReferencesY.-G. Han, "Relative Humidity Sensors Based on Microfiber Knot Resonators—A Review", Sensors, 19(23), 5196 (2019) CrossRef L.D. Koh, Y. Cheng, C. P. Teng, Y. W. Khin, X. J. Loh, S. Y. Tee, et al., "Structures, mechanical properties and applications of silk fibroin materials", Prog. Polim. Sci. 46, 86-110 (2015) CrossRef H. Tao, D. L. Kaplan, F. G. Omenetto, "Silk Materials – A Road to Sustainable High Technology", Adv. Mater., 24, 2824-2837 (2012), CrossRef Q. Li, N. Qi, Y. Peng, Y. Zhang, L. Shi, X. Zhang, et al., "Sub-mi...

Optics Letters, 2004

Testing the light scattering in the porous sol-gel silica coating.. 3.3 Testing the response of the sol gel silica coated bent fiber probe to moisture…………………………………………… 3.3.1 Testing the sol gel silica coating EWS for moisture sensing…………………………………………………. 3.3.2 Testing the sol gel silica coating EWS and absorption for monitoring low level moisture content .

Heritage

This paper presents the limitations and potential of ATR-FTIR spectroscopy applied to the study of cellulosic textile collections. The technique helps to differentiate natural fibres according to the content of lignin, pectin, hemicellulose, and wax, although some problematic issues should be considered. The spectral differences derived from the environmental humidity uptake and the plant composition are reviewed and discussed in the light of new experimental data. Diagnostic bands are proposed that can discriminate between different fibres from different plants. The contribution of ageing is also considered, demonstrating that sometimes aged fibres cannot be reliably recognised. In contrast, the potential of ATR-FTIR spectroscopy to discriminate between natural and modified fibres is discussed and proven. The best results were obtained when microinvasive ATR-FTIR spectroscopy was coupled with SEM observations. The proposed protocol was tested on microsamples of various cellulosic m...

Optical Review, 2008

Humidity induced change in the refractive index and thickness of the polyethylene glycol (PEG) coatings are in situ investigated for a range from 10 to 95%, using an optical waveguide spectroscopic technique. It is experimentally demonstrated that, upon humidity change, the optical and swelling characteristics of the PEG coatings can be employed to build a plastic fibre optic humidity sensor. The sensing mechanism is based on the humidity induced change in the refractive index of the PEG film, which is directly coated onto a polished segment of a plastic optical fibre with dipcoating method. It is observed that PEG, which is a highly hydrophilic material, shows no monotonic linear response to humidity but gives different characteristics for various ranges of humidity levels both in index of refraction and in thickness. It undergoes a physical phase change from a semi-crystalline structure to a gel one at around 80% relative humidity. At this phase change point, a drastic decrease occurs in the index of refraction as well as a drastic increase in the swelling of the PEG film. In addition, PEG coatings are hydrogenated in a vacuum chamber. It is observed that the hydrogen has a preventing effect on the humidity induced phase change in PEG coatings. Finally, the possibility of using PEG coatings in construction of a real plastic fibre optic humidity sensor is discussed.

The main focus of this thesis is on the design and development of novel fiber optic devices for relative humidity (RH) sensing with emphasis on high sensitivity, a wide humidity range, low temperature dependence, fast response time and good stability.

Indian Journal of Fibre & Textile Research, 2002

Digital control of ambient relative humidity for measurement of electrical resistance of cashmere fibre E E kht iya ri " T ex tile Eng ineering De partme nt. Yazd Univers ity .Y azd 89195-741 , Iran M J ohari Tex til e Eng in eerin g De partme nt. Ailli rkab ir Uni vers it y o r Tec hn o logy, Tehran 159 14 , Ira n and M Abe di El ec trical En g in eeri ng De partme nt , Amirkabi r Uni versity of Techno logy , Te hra n 15914, Iran Receivcd 3 1 Ju lr 200U: rCl'i.l'l'd recei" ed alld accepled 18 Oc/obe r 2001 The dy nami c equatiun s o r tes ting labo rato ry ha ve bee n stud ied to dete rmine th e el ectrical prope rties o f cash mere fibres in con stant and de finit e relati ve humi dit y accord ing to the princ iple of co ntrol des ig n. It is o bserved that the tr,lIls po rt time (dead time) has a ma jor effec t o n the s tability lim it at iun than th e sam plin g time. Us in g these limitat ions, th e eq uati o n uf propo rtional integ ra l dillere nti a l contro l has bee n obtained. T he va riation in re lati ve humidity is found to be less tha n 0.5%. The e lectri ca l resistance of th e fine unde rcoat cas hm e re fibre s is co ns ide rabl y g reater than that of the coarse ouie rcoa t cashm ere fibres. The differe nce depends on th e breeds. With the in c rea se in re lative humidity. the diffe rence in the e lectri cal resistance o f rine unde rcoat and coarse oute rcoa t cashm ere ribres dec reases.