Reference-Free Calibration for Wearable Core Body Temperature Sensor Based on Single-Heat-Flux Method

Core body temperature (CBT) is one of the useful physiological indicators that are linked to physiological changes. Wearable sensors are expected to be developed to monitor CBT easily during activities. A single-heat-flux method is one of the noninvasive techniques that estimate CBT by measuring heat flow changes near the skin with temperature sensors. The method requires calibrating parameters for estimating CBT in advance by comparing them with reference values obtained through another method. The invasive measurement method is generally used to obtain the reference values, which poses a challenge in terms of measurement burden. Here, we propose a new calibration method that does not require acquiring reference values. This method identifies calibration parameters based on the temperature history after the measurement probe is attached. It has been numerically and experimentally confirmed that the estimation accuracy by the method is equivalent to that of a general-purpose electronic thermometer. This outcome decreases the measurement workload in CBT measurement using the single-heat-flux method and significantly enhances its usability.