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Carbon Nanotubes Can be Used for Creating Extremely Sensitive Pressure SensorsScientists reveal new properties of carbon nanotubes |
By Gabriel Gache, Science News Editor
26th of October 2007, 12:35 GMT
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A recent study reveals the nanotubes can be used to create powerful pressure sensors. Researchers at Rensselaer Polytechnic Institute have discovered unique electrical and mechanical properties, during an experiment, while trying to repeatedly squeeze a 3-millimeter nanotube block and found that it was highly suitable for a potential application as a pressure sensor. The nanotube block has a linear relationship between electrical resistance and the force applied. "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 and author of the study.
The potential applications of the nanotube pressure gauge are vast, such as measuring air pressure in automobile tires, and a microelectromechanical pressure sensor that could be used in semiconductor manufacturing equipment.
Nanotube structures have been studied for a few years now, as an alternative to semiconductors, but this is the first time the material's strain-resistance relationship has been uncovered. The paper, entitled "Effects of compressive strains on electrical conductivities of a macroscale carbon nanotube block", was published in a recent issue of Applied Physics
Letters.
The experimental carbon nanotube block has been tested, while it was in a vice-like machine that applied different levels of pressure, the stress applied was measured and corresponded with the strain put on the nanotube block. As it was being squeezed, the researchers also sent an electrical charge through the block and measured its resistance, or how easily the charge moved from one end of the block to the other.
During the experiment, it was noticed that the strain they applied to the block had a linear relationship with the block's electrical resistance. The more they squeezed the block, the more the resistance decreased. The reliability and predictability of this relationship makes the carbon nanotubes block an ideal material for creating a highly sensitive pressure sensor.
The nanotube block has a function similar to the weight scale. By applying an object's own weight onto a nanotube block, it would be squeezed and its electrical resistance would decrease. By knowing the exact relationship between the electrical resistance of the carbon nanotube block, and the amount of pressure applied, the exact weight of the object can be easily calculated.
Senior researcher Victor Pushparaj showed in a study published this year, that carbon nanotubes can withstand repeated stress, yet retain their structural and mechanical integrity. Electrical resistance decreases as the block is squeezed, and the charged electrons have more pathways to move from one end of the block to the other.
Though the nanotubes' electrical resistance has a perfect linearity with the stress applied, it has been shown that this relation brakes down when the nanotube is squeezed to 65 percent of its original height.
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.
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