Development of an improved wearable device for core body temperature monitoring based on the dual heat flux principle

Objective: In this paper, a miniaturized wearable core body temperature (CBT) monitoring system based on the dual heat flux (DHF) principle was developed. Approach: By interspersing calcium carbonate powder in PolyDimethylsiloxane (PDMS), a reformative heat transfer medium was produced to reduce the thermal equilibrium time. Besides, a least mean square (LMS) algorithm based active noise cancellation (ANC) method was adopted to diminish the impact of ambient temperature fluctuations. Theoretical analyses, finite element simulation, experiments on a hot plate and human volunteers were performed. Main results: The results showed that the proposed system had the advantages of small size, reduced initial time (similar to 23.5 min), and good immunity to fluctuations of the air temperature. For the range of 37- 41 degrees C on the hot plate, the error compared with a Fluke high accuracy thermometer was 0.08 +/- 0.20 degrees C. In the human experiments, the measured temperature in the rest trial (34 subjects) had a difference of 0.13 +/- 0.22 degrees C compared with sublingual temperature, while a significant increase of 1.36 +/- 0.44 degrees C from rest to jogging was found in the exercise trial (30 subjects). Significance: This system has the potential for reliable continuous CBT measurement in rest and can reflect CBT variations during exercise.