High-sensitivity humidity sensor based on strongly-coupled seven-core fiber for respiratory rate monitoring

Abstract

In this study, an all-fiber Mach-Zehnder interferometer (MZI) respiratory rate sensor based on strongly-coupled seven-core fiber (SC-SCF) is proposed detailly. The MZI, uniformly coated with a strain-induced humidity-sensitive film of agarose, exhibits a highly sensitive response to environmental humidity variations. Thus, it could effectively translate the humidity responses caused by respiratory into measurable optical signals, enabling accurate humidity detection. In experiment, the high humidity sensitivity of 1.076 nm/%RH in the relative humidity range from 25 %RH to 50 %RH has been obtained. Through investigations on bending and surrounding refractive index (SRI) sensing, the high bending sensitivity and low SRI sensitivity have been obtained proved. And it also proves the strain-induced humidity sensing mechanism of our sensor. Besides, the respiratory rate test performs the sensor can be used in different respiratory patterns. In one respiratory cycle of normal pattern, the response time and recovery time are 0.928 and 1.304 s, respectively. The ability of our sensor for the respiratory rate monitoring under different heart rates and long-term monitoring have been displayed in our work. Our sensor not only has high sensitivity and accuracy, but also enables non-contact respiratory monitoring, which has potential applications, especially in medical and healthcare fields such as respiratory monitoring and sleep studies.