Carbon Nanotubes Used as Pressure Sensors

Researchers at Rochester Polytechnic Institute (RPI) recently discovered that when an electrically charged carbon nanotube (CNT) block is applied with a load, there is a linear relationship between the load mass and electrical resistance. The application has potential for use in pressure sensors.

RPI made the findings while conducting a study on the mechanical and electrical properties of carbon nanotubes. The block is fed an electric current that passes through with constant resistance. When a load is applied to the block, the electrical resistance changes linearly to the strain and affects the output voltage.

“What we find is as you keep increasing the load there is a change in resistance; that is how we measure if there is an increase in the voltage,” says Subbalakshmi Sreekala, a postdoctoral research assistant at RPI.

The CNT block RPI used for the study is 2.9 x 2.9x 3.4 mm and has a high level of resilience under strain. It can be compressed by as much as 45 percent of its original dimensions and still maintain linearity; not until 65 percent does it fail to have a linear relationship of strain to resistance. “For every load you apply there will be some change of dimension for the system, so we measure the change,” says Sreekala.

After this high level of pressure is applied, the block will reform to its original shape and size. “Other materials would break down by then; they might have mechanical failure,” she says.

The CNTs are grown into a block through traditional CVD methods and are a pure carbon structure without integrated polymers or composites. They have a very long life and would not need to be replaced regularly if used in a pressure sensing device.

Other potential uses of these CNT blocks include strain transducers, micro electronic machines (MEMs) and automobile tire pressure gauges. “You can use them anywhere where the system is very small,” says Sreekala.