Development of Compact Load Cell Using Multiwall Carbon Nanotube/Cotton Composites and Its Application to Human Health and Activity Monitoring

Compact load cells have been developed using multiwall carbon nanotube/cotton (MWCNT/cotton) composites, whose performance has been optimized by varying the concentration of MWCNTs and the thickness of the composite. The sensitivity of the load cell, which is defined as the ratio of the change in the relative electric resistance to the change in applied pressure, is measured to be in the range of 180-0.20 kPa-1 for applied pressures of 8.84 Pa-884 kPa (F=1.0 mN-100 N). The load cells show a rapid response in situations with a frequently changing force, with response times τ1/2 of 4.5 and 5.0 ms for the application and release of load, respectively. The load cell demonstrates high reproducibility in tests involving more than 11,200 compression/relaxation cycles. It also has high reproducibility in different harsh environments and has a good electric-conductance recovery property. The load cell is successfully used to monitor the time-varying center of gravity of a human foot, which can be applied to the diagnosis of sick and healthy people. The MWCNT/cotton load cells can be used as wearable and flexible devices for monitoring human health.