Flexible multi-modal sensors based on CNT hollow spheres/PDMS composites for human motion recognition and colloid concentration detection

Because flexible sensors with multi-modal responses are essential for applications in the complex environment of wearable products, a unique carbon nanotube (CNT) hollow-sphere scaffold is fabricated using self-assembling of microspheres and microwave irradiation to achieve flexible strain, pressure, and laser sensors. The CNT hollow-sphere scaffold comprising intertwined CNTs is featured with a sophisticated conductive network, large tensile and compressive deformability, intrinsic photothermoelectric nature, and good accommodation for poly-dimethylsiloxane (PDMS) matrix. Thus, the fabricated CNT hollow spheres/PDMS composite sensors showed good responses to the applied strain (a high gauge factor exceeding 55000 in the strain region of 95-107%, 27 ms response time, and over 20000 cycles durability at 40% strain), pressure (a gauge factor of 0.07-3.15 kPa-1 with a wide sensing range (up to 248 kPa pressure), and laser irradiation (0.066 s-1 at 5 s of 532 nm laser irradiation). Moreover, their uses in body movement detection, healthcare, tactile perception, and colloid concentration detection are demonstrated. It is believed that the CNT hollow spheres/PDMS composite sensors will pave the way for practical applications for future wearable electronic devices, which could recognize human motion as well as sense air quality and disease diagnosis.