Carbon-Nanotube-Based Optical Fiber Sensor With Rapid Response for Human Breath Monitoring and Voiceprint Recognition

This letter describes the development of a simple and novel optical fiber relative humidity (RH) sensor to be used for breath monitoring and voice recognition. The proposed sensor utilizes an intensity modulation phenomenon via evanescent wave (EW) absorption. The optical fiber sensor (OFS) employs a chemically synthesized nanostructured sensing film composed of multiwalled-carbon-nanotube-doped chitosan coated over a 5-cm length of a centrally decladded, straight, and uniform plastic cladding silica (PCS) fiber. A comprehensive experimental investigation is carried out to analyze the response characteristics of the proposed sensor. A linear response over the dynamic range of ∼70–97% RH with a sensitivity of 0.3041 dB/% RH is observed for the developed sensor. Furthermore, the resolution of the developed RH sensor is observed to be ±0.13% RH. An average response and recovery times of 100 and 150 ms are recorded during the humidification and dehumidification process. In addition, the proposed sensor demonstrates a high degree of repeatability, reversibility, and stability. Moreover, the developed sensor has the ability to detect RH fluctuations within exhaled air during both breathing and speaking.