Beams of ultrasonic sound waves project a force field in front of screens, making it feel as though a user is touching an invisible 3D surface.
Imagine waving your hand in front of a map on your computer screen and feeling a force push back against you. The strength of the force could be proportional to the population or crime rate, say, of each city you pass over.
Tom Carter and his colleagues at the University of Bristol, UK, will demonstrate just such a system this week at the User Interface Systems and Technology conference in St Andrews, UK.
Called UltraHaptics, it uses an array of 320 ultrasound speakers set behind a touchscreen to generate beams of high-frequency sound waves. The waves are linked to the software running the displayed content and interact to create hotspots that give different sensations as people move their hands.
"What you feel is a vibration. The ultrasound exerts a force on your skin, slightly displacing it. We then turn this on and off at a frequency suited to the receptors in your hand so that you feel the vibration," says Carter.
"A 4-hertz vibration feels like heavy raindrops on your hand," he says. "At around 125 Hz it feels like you are touching foam and at 250 Hz you get a strong buzz."
UltraHaptics could be used to make invisible sliders for in-car entertainment systems, Carter says, so drivers could feel their way to the desired volume. And people whose hands are often dirty, like chefs or mechanics, could use invisible haptics to flip through manuals or recipes.
"This ultrasound approach is great in that it tackles a hard problem in producing the sensation of a directed force in mid air," says Patrick Baudisch, who works on novel interactive technology at the University of Potsdam in Germany.
One problem remains, however: the sounds can be heard by dogs, which could cause all sorts of issues. Pooch owners should be able to rest easy though. "We can increase the frequency to take it out of that range," says Carter.