Stanford University researchers have used carbon nanotubes and silicone to build sensors that can stretch and deform, always returning back to its original shape.
Two layers of silicone, coated by single-walled carbon nanotubes, are separated by another silicone layer. Silicone can store electrical charge, and pressure on the layers alters how much charge it can store.
The carbon nanotubes, which have positive and negative terminals, pick up changes in the amount of charge in the silicone. The change in the amount of charge relates to the amount of pressure being put on the silicone. That helps detect tension. Altogether, the pattern of pressure provides a picture of what the sensor is experiencing. Just like skin, the material can sense whether it's being pressed or pinched.
One reason the material seems to have these odd properties is the behavior of the nanotubes. When the nanotubes are sprayed onto the silicone, they are oriented randomly. Stretch the silicone, and the tiny clumps of nanotubes get pulled into alignment along the direction of the stretch. Once released, the silicone bounces back into shape and the nanotubes make little spring-like structures, which can be stretched again. After some pre-stretching, the combination silicone-nanotube material will always return to its former shape.
The obvious use for this material is in prosthetic limbs, where one of the big problems is giving the limb a sense of “feeling” to go along with motion. While there are artificial limbs being developed that can be controlled by thought, it continues to be a challenge to generate feedback that varies with pressure. This material may be one step toward solving that problem.
Image: Stanford University