Plastic Optical Fiber Tapered Sensor for Breathing Sensing

Vital signs monitoring of the human body is an important factor of diagnosing health conditions. In this paper, a high-precision plastic sensor used to monitor respiration is designed and demonstrated. The sensing system based on a tapered plastic optical fiber (POF) uses the flashlight of the mobile phone as the light source. In the experiment, a paper cup is used as the reaction area for respiration and the POF is tapered to improve the sensitivity. Before measuring respiratory rate, a manual press method is used to obtain the output waveform of the sensor via applying a fixed press-times. Then, the data of the sensor is calibrated and fitting lined using the press times and the fundamental frequency of the obtained waveform. Through the calibration curve, it can be found that the proposed sensor has a high linearity with a R2 of 0.999. During the experiments, it is indicated that the actual respiration frequencies agree well with the fitted curves of the data calibration. It has been proved that the tapered POF sensor has extremely high accuracy. Moreover, the high repeatability of the sensing system has been proved. Compared with traditional breathing sensor, the proposed POF sensor possesses the characteristics of low-cost, simple operation and high accuracy.