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New sensors could lead to artificial skin.

Even the best touch-sensitive robots with soft, forgiving mechanical hands have trouble with this task because they use large discrete sensors that only supply feedback from small areas of the gripper. That makes their touch-only movements slow and awkward at best.

That may be about to change. A new type of transistor uses piezoelectric nanowires to convert changes in pressure directly into electrical currents that control sensory feedback.

A team led by Zhong Lin Wang, a Regents' professor at Georgia Institute of Technology's School of Materials Science and Engineering, has demonstrated large area sensor arrays with enough resolution to mimic human skin.

The key to the technology lies in a unique type of transistor developed by Wang. Most transistors consist of two terminals, one positive and the other negative, and a gate activated by electric current that controls the flow of electrons between the terminals. In most transistors, the gate current comes from an external power source.

Wang's insight was to use piezoelectric materials, which convert mechanical energy into electrical current, to activate the gate. Each transistor uses approximately 1,500 individual nanowires to sense pressure. Rising pressure strains the nanowires and increases the amount of electrical current flowing into the gate.

Wang calls these touch-sensitive transistors taxels (a play on pixels) and each one of them is a fully functional sensor. Their strength, however, is that they are relatively easy to integrate into a large area array without complex control circuits.

To demonstrate the technology, Wang produced a 1 square centimeter array of 8,464 taxels. The array achieves better than 100 micron resolution, and senses pressure changes down to 10 kilopascals. This is 300 to 1000 times denser than similar systems reported by other researchers, and according to Wang, it has the sensitivity of a human fingertip.

Robots are only one application for the new sensor technology. It could be used to verify identity by matching the speed and pressure of a signature, provide better feedback for surgical instruments and other haptic devices, and perhaps create prosthetics to a sense of touch.

A NEW TYPE OF TACTILE sensor that is nearly as sensitive as human skin may one day enable robots to do something humans take for granted-casually wrap their fingers around a cup of coffee without looking.

GLOBAL CONCENTRATIONS OF CARBON DIOXIDE IN THE ATMOSPHERE ARE SOON EXPECTED to reach 400 parts per million-higher than any time in the past million years. One bit of good news is that U.S. greenhouse gas emissions fell in 2011 to the equivalent of 6,702 million metric tons of carbon dioxide, about what they were in 1996, according to the U.S. Environmental Protection Agency. About half the drop can be accounted for by the reduced burning of fossil fuels in the electricity sector, where cheap natural gas has replaced some coal-fired generation. Global emissions, however, continue to rise.

6.9% DROP IN ANNUAL U.S. GREENHOUSE GAS EMISSIONS SINCE 2005

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Title Annotation:TECH BUZZ
Comment:New sensors could lead to artificial skin.(TECH BUZZ)
Author:Brown, Alan S.
Publication:Mechanical Engineering-CIME
Geographic Code:1USA
Date:Jun 1, 2013
Words:492
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