Characterisation of low-cost stretchable strain sensors for wearable devices

Abstract

This paper presents the characterisation of the three distinct materials considered to be used as a resistance-type strained-based sensor on a wearable device. Other performance parameters besides the usual linearity, sensitivity, working range, and hysteresis were also considered. These included the resistance variations caused by a changing temperature, the effects of moisture on the sensor's resistance, and the stress coefficient of resistance. These were necessitated by the nature of the operational environment of most wearable sensors, which may entail the heat introduced to the sensor due to its proximity to the human body, the moisture from perspiration and the limited amount of force that a feeble patient say, can be able to exercise on the sensor. The selected sensor had a high degree of linearity, as established using the linear regression model (R2 = 0.94), had a decent sensitivity (gauge factor = 1.7), a working range of at least 30% strain, and suffered insignificant hysteresis (6.3%). This sensor also had a moderate stress coefficient of resistance (0.11%/KPa) and was unaffected by the changes in temperature and moisture. And the best part is that it is also low-cost.