Wearable FBG Sensor System for Respiratory Strain Measurement during Daily Activities

This study developed a wearable fiber Bragg grating (FBG) sensor system and explored the measurement of respiratory rate during daily activities of life such as standing, walking, and running. The measurement system used was a wearable FBG interrogator that we developed ourselves. An FBG sensor, which is an optical fiber type strain sensor, was installed on the inner surface of the belt, and this belt was wrapped around the body. The respiratory cycle calculated from the respiratory strain signal measured by the FBG sensor was almost identical to the reference respiratory cycle measured by the temperature sensor. Initially, the pressure applied by the belt was found to cause discomfort over prolonged use. This issue was resolved by further re-fining the belt shape. Respiratory strain was almost accurately measured with the improved belt even when the following daily activities occurred: standing, walking at 4 km/h, and running at 10 km/h. Additionally, it provided a high S/N ratio respiratory strain signal even when participants were asked to walk in a hallway and up and down stairs. The sensor system developed in this study can help measure respiratory rate in daily life without interference.