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December 16, 2016

Ultrasonic vibrations cause fingers to bounce on touchscreens

Researchers at Northwestern University have discovered why applying ultrasonic vibrations to a flat, featureless glass plate makes it feel slippery. In this image, warmer colors indicate areas where the vibration-induced air cushion is stronger.

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Haptics researchers have long known that applying ultrasonic vibrations to a flat, featureless glass plate makes it feel slippery. But they have also long debated why this occurs.

Now, J. Edward Colgate, a professor of mechanical engineering and the Allen K. and Johnnie Cordell Breed Senior Professor in Design, and his team at Northwestern University have discovered that the vibrations reduce friction by causing the fingertip to bounce on pockets of trapped air.

Colgate, a haptics technology pioneer, says understanding this underlying reason is extremely useful and will help researchers engineer more sophisticated devices that not only vary friction but do other things, such as exert forces on the finger.

The research was supported by the National Science Foundation (grant IIS 13-02422).

To learn more about this research, see the Northwestern University news story Mystery solved: The case of the slipping finger. (Date image taken: May 2016; date originally posted to NSF Multimedia Gallery: Dec. 16, 2016)

Credit: M. Wiertlewski/Center for High-rate Nanomanufacturing

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