High-precision, stretchable kirigami-capacitive sensor with ultra-low cross-sensitivity for body temperature monitoring

Wearable temperature sensors meeting the resolution of medical-grade thermometers are needed to continuously monitor skin temperature variations indicative of diseases and sports performance. Herein, we present a new technique for creating stretchable capacitive sensors with a temperature resolution of 0.14 °C and minimum cross-sensitivity to mechanical stretch. Two complementary strategies were employed to minimize the stretch-sensitivity and achieve high temperature resolution: (a) increasing the temperature sensitivity by using a dielectric core material of positive temperature coefficients of permittivity and thermal expansion, and (b) reducing the cross-interference of mechanical deformation by optimizing the kirigami pattern. The optimized kirigami-capacitive wearable temperature sensors with a thermoplastic polyurethane core sandwiched between electrodes made of silver nanowires exhibit a high temperature sensitivity of 0.007 °C-1 with an excellent linearity of 0.998. Computational modeling of kirigami geometry effects on strain and temperature sensitivities of capacitive sensors reveals that the optimized kirigami design can reduce the strain cross-sensitivity by a factor of 3125, which enables capacitive temperature sensors to achieve the resolution of point-of-care medical devices. The combined characteristics of high sensitivity, linearity, breathability, and stretchability make the new capacitive sensors a promising candidate for medical-grade wearable temperature sensors.