Stress Loading Detection Method Using the FBG Sensor for Smart Textile

In this paper, we propose a physiological stress measurement method that uses a fiber Bragg grating (FBG) sensor. There are several points on the surface of the human body at which the pulse wave can be measured, and when an FBG sensor can be positioned at any of these points, to measure the pulse wave signal. When a person is under stress, their pulse rate increases and the peak interval in the measured pulse wave signal becomes shorter. This peak interval change can be measured using the FBG sensor and analyzed using a Poincaré plot; the stress load can then be detected based on the shift in the plot position. The points on the Poincaré plot shift toward the lower left direction because of the stress loading. Depending on the amount of applied stress, the length by which the plot shifts changes. When the proposed measurement method is used, it is possible to continuously monitor a subject for stress by simply installing the optical fiber at a pulsation point. When optical fibers are woven into textile products, it becomes possible to detect stress load by wearing a modified garment. Therefore, this measurement method can be applied as a wearable stress sensor in smart textiles.