Sensors made from carbon nanotubes could offer a superior alternative to current activity tracking technology. Devices developed at the University of California, San Diego, are flexible enough to bend within layers of fabric, and can track specific types of motion as well as recording vital signs such as temperature and heart rate. These developments are promising for real-time monitoring of patients living at home, through telemedicine and those working in extreme environments, like astronauts in space.
PhD student Long Wang and Professor Kenneth J Loh, researchers in the UCSD’s department of structural engineering, produced the flexible sensors using carbon nanotubes (CNTs) and fabric with an ingenious, cost-effective manufacturing process (Smart Mater. Struct. 26 055018). An ink consisting of CNTs and latex is mixed together and sprayed onto glass, where it is then annealed to produce a freestanding thin-film network of nanotubes. Once two electrodes have been attached, the film is then sandwiched between two layers of fabric and ironed together to produce a flexible fabric sensor.
These multipurpose sensors not only record heart rate, but they can also accurately track motion in a finger and even monitor respiration. When attached to a finger, the flexible nature of the thin film allows the sensor to bend and flex as the finger moves. This change in shape alters the electrical resistance across the film, which makes it possible to determine the bending angle.
Similarly, if strapped around the torso, the film changes in shape as the chest expands during inhalation, subsequently changing the resistance. When the person breathes out, the film returns to its original shape and the resistance drops again.
The sensor can also be used to monitor skin temperature. As the film is heated, there is again a change in the electrical resistance. These changes can be calibrated using measurements taken with a thermocouple, which allows the resistance change to be converted to the temperature of the skin.
Sensors like this are useful beyond the realms of logging the stats of your run or cycle ride. It’s still early days, but Wang and Loh have successfully combined an easy fabrication route with the versatility needed to take a number of important measurements. Their results show that the technology is on track to be used extensively for easy, non-invasive, real-time monitoring of individuals in a variety of environments.
