MWCNTs/PDMS composite enabled printed flexible omnidirectional strain sensors for wearable electronics

Conductive composites have been used for flexible strain sensors due to their tunable and traceable resistance changes when applying strain. To-date, most flexible strain sensors were simple straight strips for sensing ability studies. In this paper, formulated MWCNTs/PDMS composite ink was screen printed to form patterned flexible strain sensors to address variety needs in strain measurements: sensors with longitudinal serpentine lines for unidirectional and bidirectional strains, sensors with circular designs for omnidirectional strains, and strain gage rosette to determine primary strain and its direction. The printed flexible sensors had high gage factor of 1.55 with good linearity up to 100% deformation. Good sensing stability, repeatability, and fast dynamic response were demonstrated by more than 4000 strain cycles without degradation. The printed composite-based sensors had good long-time usability and environmental stability according to the results of 85 °C/85% RH temperature/relative humidity acceleration tests. With all above unique properties and good performances, the printed strain sensors were used as wearable electronics for motion detection, sport and rehab training, and structure health monitoring. The composite materials and additive screen-printing process can be scaled-up readily for further application development and product integration.