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A chemical engineer at Stanford University has developed a pressure sensor based on a pair of transparent films of single-walled carbon nanotubes. The nanotubes act as springs, letting the sensor accurately measure forces on it as it is being pulled like taffy or squeezed like a sponge.
The nanotube layer is created by suspending hollow nanotubes in a liquid, then spraying the liquid onto a thin layer of silicone which is then stretched. The stretching aligns some of the randomly oriented clumps of nanotubes into lines in the direction of stretching. When the silicone is released and snaps back to its original shape, the nanotubes buckle and form structures resembling nanoscale springs. The material, along with the lines of nanotubes, can then be repeatedly stretched in any direction without permanently changing the shape of the silicone.
The sensors consist of two thin sheets of nanotube-coated silicone oriented so that the coatings face each other, with another layer of more-easily deformed silicone sandwiched between them. This middle layer stores electrical charge, much like a battery. Pulling or squeezing the sensor changes the amount of electricity this layer can store. This change is detected by the two nanotube films, which act like positive and negative terminals on a battery.
So far, the Stanford researcher has built sensors that can detect pressures ranging from 20 mg to 30,000 lb. She is trying to make the sensor more sensitive and develop algorithms that will let users determine if the sensor is being stretched or compressed. This sensor technology could lead to touch-sensitive prosthetics and robots, as well as improved computer touchscreens.