Fig. 2: Design of the sensor part in the device for reliable SH and TEWL measurement.

a Exploded-view illustration of the sensor part: a cap, SH sensor, TEWL sensor, and a breathable chamber. b An optical image of the sensor part. c Cross-sectional and top view of the temperature distribution induced by the heaters on the skin for 2 s. d Transient temperature (∆T) response generated by different heating time on SH. e Illustration of the wet-cup method set up to generate different water vapor flux values for calibration of the TEWL sensor. f Graph of humidity change inside the chamber due to the closed breathable chamber. g Calculating of TEWL using the linear squares method. h Graph of ventilation time according to chamber height from semi-permeable membrane (n = 3). n represents the number of technical independent replicates. Data were expressed as mean ± SD. i Repeatability of measurements of the TEWL sensor. j TEWL measurement using reference data (wet-cup method), a commercial sensor and our sensor according to the number of semipermeable membrane layers (n = 5). n represents the number of technical independent replicates. Data were expressed as mean ± SD. k Illustration of the ventilation experiment. Change in the amount of water evaporation depending on the vertical (l) and horizontal distance (m) (n = 5). n represents the number of technical independent replicates. Data were expressed as mean ± SD. Evaporation simulation results for the unbreathable chamber (n) and breathable chamber (o).