Abstract
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™ D4 and microbiology agar were characterized and tested using two types of optical sensors. First, optical fiber Fabry–Perot (FP) tips were made, which allow the dynamical measurement of the polymers’ 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.
Highlights
The real-time monitoring of relative humidity (RH) in scientific and industrial applications is of extreme importance, and many types of sensors were developed
The usage of hydrophilic polymers in optical fiber sensors (OFS) is a thoroughly explored field of research [1,2,3,4], with most of these works using them as a functionalization layer that responds to RH variations
While the increase of humidity leads to a decrease of signal amplitude in the case of the agar Fabry–Perot interferometers (FPI), the opposite is seen in the poly(ethylene glycol) (PEG), where the amplitude of the signal displays a clear increase with the increase of humidity
Summary
The real-time monitoring of relative humidity (RH) in scientific and industrial applications is of extreme importance, and many types of sensors were developed. The usage of hydrophilic polymers in optical fiber sensors (OFS) is a thoroughly explored field of research [1,2,3,4], with most of these works using them as a functionalization layer that responds to RH variations. A consistent, continuous measurement of the properties of four different polymers is reported These RH responding polymers are poly(vinyl alcohol) (PVA), poly(ethylene glycol) (PEG), HydromedTM D4, and microbiology Agar. The work here presented provides the characterization of the optical and expansion properties of these materials, which can be of extreme importance for fabrication and optimization of relative humidity optical sensors
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