Development of flexible and wide-range polymer-based temperature sensor for human bodies

In this paper, we propose a thin, flexible, polymer PTC sensor with a wide temperature measurement range. A polymer PTC sensor consists of several polymers and conductive filler and its resistivity changes with an increase in temperature. Conventionally, it has been proposed as a flexible temperature sensor. However, no research has yet achieved enough flexibility and a wide temperature measurement range that is sufficient for measuring the human body temperature; furthermore, polymer PTC sensors have not yet been put to practical use. In this research, by using two specific monomers as the raw materials of the polymers and by using several of such polymers for fabricating one sensor, we succeeded in making a new polymer PTC sensor which has not only a wide temperature measurement range (25°C to 45°C) but also enough flexibility to function with a very small thickness (33 μm). Resistivity of the proposed polymer PTC changes by 4 orders in accord with an increase in the temperature from 25°C to 45°C. These characteristics are more suitable for the wearable temperature sensors and medical devices than those of conventional polymer PTC. Wide temperature measurement range helps us to measure temperature at several body parts in different environments, and flexibility increases the adhesiveness of the sensor to the human body. Moreover, high sensitivity makes readout circuits simple and it is easy to calculate temperature from the resistivity of the sensor.