Finding Human Thermal Comfort with a Watch-type Sweat Rate Sensor

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KAIST developed a watch-type sweat rate sensor. This subminiature device can detect human thermal comfort accurately and steadily by measuring an individual’s sweat rate.

It is natural to sweat more in the summer and less in the winter; however, an individual’s sweat rate may vary in a given environment. Therefore, sweat can be an excellent proxy for sensing core body temperature.

Conventional sweat rate sensors using natural ventilation require bulky external devices, such as pumps and ice condensers. They are usually for physiological experiments, hence they need a manual ventilation process or high power, bulky thermos-pneumatic actuators to lift sweat rate detection chambers above skin for continuous measurement. There is also a small sweat rate sensor, but it needs a long recovery period.

To overcome these problems, Professor Young-Ho Cho and his team from the Department of Bio and Brain Engineering developed a lightweight, watch-type sweat sensor. The team integrated miniaturized thermos-pneumatic actuators for automatic natural ventilation, which allows sweat to be measured continuously.

This watch-type sensor measures sweat rate with the humidity rising rate when the chamber is closed during skin contact. Since the team integrated thermos-pneumatic actuators, the chamber no longer needs to be separated manually from skin after each measurement in order for the chamber to ventilate the collected humidity.

Moreover, this sensor is wind-resistant enough to be used for portable and wearable devices. The team identified that the sensor operates steadily with air velocity ranging up to 1.5m/s, equivalent to the average human walking speed.

Although this subminiature sensor (35mm x 25mm) only weighs 30 grams, it operates continuously for more than four hours using the conventional wrist watch batteries. 

The team plans to utilize this technology for developing a new concept of cognitive air-conditioning systems recognizing Human thermal status directly; while the conventional air-conditioning systems measuring air temperature and humidity.

Professor Cho said, “Our sensor for human thermal comfort monitoring can be applied to customized or smart air conditioners. Furthermore, there will be more demands for both physical and mental healthcare, hence this technology will serve as a new platform for personalized emotional communion between humans and devices.”