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Cellulose, as a fully renewable, biodegradable, and biocompatible material, creates new possibilities for optical fiber (OF) sensor applications. Cellulose OFs are highly hygroscopic, exhibiting rapid wetting and drying properties with water and moisture, easily functionalized, and can be either made water-resistant or water-soluble. These fibers are not aimed towards replacing the existing glass or polymer OFs in telecommunication or in current sensing applications, rather cellulose OF sensors can open new application areas where the reactive materials are required. For example, compared to glass or polymer OFs, cellulose OFs are porous and allow liquid transport in and out of the fiber. Moreover, the cellulose waveguide material itself can be chemically functionalized. Such cellulose OFs fit well with human health monitoring where the new possibilities that cellulose offers can be utilized. Here we demonstrate a face mask that contains regenerated cellulose (RC) OF with a 1.8 dB/cm attenuation constant for respiratory rate monitoring. RC is a class of man-made cellulose materials that includes commonly materials like rayon textiles and cellophane films. The cellulose fiber inside the face mask rapidly absorbs moist and dries between each breath, which causes a periodic change in optical power transmitted through the fiber. A face mask does not prevent fast drying of the fiber. Such RC fiber fits well to respiratory rate monitoring because it exhibits good mechanical performance in both dry and wet states. Cellulose OF length was about 5 cm long with a loop-type sensor structure. Measured respiratory rates varied between 16-54 breaths per minute.
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