Nanotube pressure sensor

Blocks of carbon nanotubes can be used to create effective and powerful pressure sensors, according to researchers at Rensselaer Polytechnic Institute.

Taking advantage of the material’s unique electrical and mechanical properties, researchers repeatedly squeezed a 3mm nanotube block and discovered it was highly suitable for potential applications as a pressure sensor. No matter how many times or how hard they squeezed the block, it exhibited a constant, linear relationship between how much force was applied and electrical resistance.

’Because of the linear relationship between load and stress, it can be a very good pressure sensor,’ said Subbalakshmi Sreekala, a postdoctoral researcher at Rensselaer.

A sensor incorporating the carbon nanotube block would be able to detect very slight weight changes and would be beneficial in any number of practical and industrial applications, Sreekala said. Two potential applications are a pressure gauge to check the air pressure of automobile tyres, and a microelectromechanical pressure sensor that could be used in semiconductor manufacturing equipment.

Despite extensive research over the past decade into the mechanical properties of carbon nanotube structures, Sreekala and his team are the first to explore and document the material’s strain-resistance relationship.

In the laboratory, the researchers placed the carbon nanotube block in a vice-like machine and applied different levels of stress. They took note of the stress applied and measured the corresponding strain put on the nanotube block. As it was being squeezed, they also sent an electrical current through the block and measured its resistance.

The research team discovered that the strain they applied to the block had a linear relationship with the block’s electrical resistance. The linear strain-resistance relationship holds true until the block is squeezed to 65 per cent of its original height. Beyond that, the block’s mechanical properties begin to fail and the linear relationship breaks down.

The team is currently thinking of ways to boost the nanotubes’ strength by mixing them with polymer composites to make a new material with a longer-lived strain-resistance relationship.

’The challenge will be to choose the correct polymer so we don’t lose efficiency, but retain the same response in all directions,’ Sreekala said.