Pulse sensor based on cascade grating using silica gel package

A pulse sensor based on cascaded grating is proposed. Cascaded gratings composed of two fiber Bragg gratings with the same parameters are implanted into the silicone wristband. One fiber Bragg grating is used as a sensing grating to sense the pulse signal, and the other grating is used as a matching grating for demodulation. Because the parameters of the two gratings are exactly the same, their reflection peaks overlap, and the reflection spectrum of the sensor shows a single reflection peak. The pulse signal modulates the strain state of the sensing grating under the action of stress, resulting in the shift of the central wavelength of the reflection peak of the sensing grating, which leads to the change of the reflected light intensity of the sensor. By monitoring the reflected light intensity of the sensor, the measurement and extraction of pulse are realized. In the experiment, the pulse of healthy young and old male subjects, and the same healthy male subjects at 8 am/pm are tested. The results show that the sensor can effectively extract the pulse feature points of different subjects, and the test results are in line with the pulse theory of traditional Chinese medicine. When the ambient temperature changes, the reflection peaks of the two gratings shift in the same direction at the same rate, and the reflected light intensity of the sensor remains stable, so the sensor is not affected by the ambient temperature. In addition, the sensor has the advantages of simple structure, convenient demodulation and low cost. There are potential applications in pulse measurement.