For years now, scientists across the globe have strived to find a method that gives robots an accurate sense of touch, and with good reason. A robot with an improved ability to feel would be better equipped to identify objects, judge its movements with greater care, and perform more tasks overall. In the latest step towards that goal, researchers at Georgia Tech have crafted a new type of touch-reactive material that's sensitive enough to read fingerprints and could provide robots with a sense of touch that resembles our own.

The heightened tactility of the material comes from thousands of piezotronic transistors, each containing about 1,500 nanowires that are between 500 and 600 nanometers in diameter. Unlike most touch screens that measure changes in resistance or capacitance to detect where your finger is, these transistors sense changes in their own polarity when pressure is applied. This is due to the nanowires' zinc oxide composition, which simultaneously gives them piezoelectric and semiconducting properties.

Over a period of almost three years, the research team of Zhong Lin Wang, Wenzhuo Wu, and Xiaonan Wen were able to chemically grow hundreds of arrays measuring 92 x 92 transistors, all of which were arranged vertically to form "taxels" that produce individual electronic signals when touched. The taxels were sandwiched between layers of indium tin oxide and gold to link them together, then coated with a polymer that blocks moisture and corrosion known as Parylene. The resulting arrays have a density of 234 pixels per inch and can register pressures starting at 10 kilopascals (1.5 psi). According to the developers this makes them almost as sensitive as a human fingertip.

The arrays are transparent, flexible, and quite durable – even remaining operational after being submerged in saline and distilled water for 24 hours – which opens them up to a wide range of applications, particularly for touchscreens and artificial skin.

The research team foresees the material being used for advanced touchscreens that can read fingerprints or even register the exact pressure used at different points of a signature to enhance security. The advanced tactile sensors could also help in creating prosthetic skin with a greater sense of touch for both robots and prosthetic limbs, which could in turn lead to life-like features, such as hair follicles that react more realistically.

The project is undergoing further development with support from the Defense Advanced Research Projects Agency (DARPA), the National Science Foundation (NSF), the U.S. Air Force (USAF), the U.S. Department of Energy (DOE), and the Knowledge Innovation Program of the Chinese Academy of Sciences. In the future, the team says it could increase the material's sensitivity even further by reducing the number of nanowires in the taxel arrays from several hundred to just one.

Source: Georgia Tech

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