Carbon nanotubes find new employment in pressure sensors

Posted by Rick C. Hodgin

Troy (NY) - Researchers at Rensselaer Polytechnic Institute have developed a novel approach toward utilizing one of the most essential elements on the face of the earth, Carbon.  Nanotubes built from carbon exhibit a unique property.  They have an ability to be nearly perfectly linearly flexible, and without losing any of their flexibility after repeated distortion cycles.  This ability translates into a very accurate tool for measuring pressure.

Researchers were able to take a 3mm long carbon nanotube and subject it to repeated squeezing.  They found that no matter how hard they squeezed, or how often they repeated the squeezing, it always equated the same amount of force applied to a constant change in electrical resistance.  They found that the carbon nanotube could be squeezed up to 65% of its maximum without any permanent deformation or breaking.  Beyond that point the material would break as the carbon chains were physically broken, and the material could only be squeezed in a particular orientation.

The carbon nanotubes can be bundled together into a block form for even greater force.  Since the carbon nanotubes exhibit a constant pressure when squeezing, they can be sized based on the workload.  This illustration shows how the carbon nanotubes work together an deform uniformly across the many strands.

The researchers used a very tiny vice for the experiments.  They applied a force which squeezed the nanotube while, at the same time, they measured the electrical resistance with electrodes.  They found that it is a perfectly linear relationship between resistance and pressure applied.  The more pressure, the lower the electrical resistance.  The researchers were quite surprised and happy to discover that the line was completely linear.

Two suggested immediate applications are an accurate pressure gauge to check the air pressure of automobile tires (while in use, constantly sending back wireless data), and a microelectromechanical pressure sensor that could be used in semiconductor manufacturing equipment.  Additional uses could be micro-changes in weight measurements as well as other change-sensing devices.  The research team is also looking at composite materials which will allow the breaking strength to exceed 65% of maximum, and to move in multiple directions with identical properties.

The Rensselaer Polytechnic Institute is the United States' oldest technical university, founded in 1824.  The funding for this project came from Focus Center New York for Interconnects.  Carbon nanotubes have had a host of proposed uses as their unique properties allow them to be suitable for heat transfer, structural members in nano-machines, electrical conductors and insulators based on doping agents, and several more uses.  Carbon nanotubes are presently very expensive to create, though there are several processes under development which could change that.