Design Of Vital Sign Monitoring Sensor Based On Modal Interference

In recent years,optical fiber sensors have occupied a place in the field of sensing due to strong anti-electromagnetic interference,high sensitivity,large dynamic range,light weight and so on.The emergence of optical fiber sensors based on modal interference has further promoted the development of optical fiber sensors.It breaks the bondage of traditional interferometric optical fiber sensors and uses the interference between modes to realize sensing.In this paper,we firstly study the theories of mode excitation in Dual-mode Fiber(DMF)and Multi-mode Fiber(MMF),and then use the theories of mode excitation to fabricate vital sign monitoring sensor based on DMF and MMF.Finally,the monitoring results show that both sensors can achieve simultaneous monitoring of respiratory signals and heartbeat signals.Two kinds of sensors are fabricated by core-offset fusion,i.e.core-offset fusion of a section of DMF or a section of MMF in two sections of Single-mode Fiber(SMF).In order to ensure the best sensing performances of two kinds of sensors,we select the manufacturing parameters of two kinds of sensors by combining theories with experiments.Firstly,the mode excitation theories in DMF and MMF are studied,and the numerical simulations are carried out according to the mode excitation theories to find the optimal core-offset fusion parameters,which then are verified by experiments.Then,the optimal lengths of sensing fibers and the appropriate layouts of sensing fibers are selected through experiments.Finally,the sensor cushions are made according to the above parameters,and the respiratory signals and heartbeat signals of different volunteers are monitored.The real-time comparisons with the medical reference sensors are made to analyze the accuracy of the proposed sensors.The two kinds of vital sign monitoring sensors designed in this paper are the first time to realize simultaneous monitoring of respiratory signals and heartbeat signals using the principle of modal interference.Compared with the medical reference sensors,the correlations of respiratory signals exceed 0.9,and the correlations of heartbeat signals exceed 0.82.It can be seen that the two sensors have good monitoring effect.In addition,the two vital sign monitoring sensors belong to non-wearable monitoring,which greatly improves the comfort of the monitoring process.