People who are blind can read Braille in mid-air using their hands thanks to a grid of speakers that emit ultrasound waves. The device creates points in the air that are similar to the dots that form Braille characters.
“On the skin this feels like a gentle breeze of air,” says Viktorija Paneva at the University of Bayreuth in Germany. The mid-air dots are perceptible on a person’s palm when they about 20 centimetres from the device, which consists of a 16 x 16 grid of ultrasound speakers, each with a diameter of one centimetre.
These speakers emit ultrasound waves towards a point in mid-air. At this focus point, all the waves are in phase with each other. “That’s why we have this strong acoustic force,” says Paneva.
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A single Braille character consists of a combination of six dots in a 2 x 3 grid arrangement. Paneva and her colleagues devised three different methods of presenting Braille characters and asked 11 blind participants to test the device.
In one method, the dots that make up a Braille character were presented simultaneously. In another, each dot was presented sequentially, dot by dot, for 200 milliseconds at a time. In the third method, the dots were presented one row at a time. In each case, the dots were spaced about 3 centimetres apart from each other.
The dot-by-dot method had the highest average accuracy, with 88 per cent of characters being correctly identified. The accuracy was limited by participants’ ability to distinguish the different points hitting their palm, says Paneva. To mitigate this, the team used slightly different ultrasound wave frequencies for the six dots that make up each Braille character, to make it easier to distinguish the different dots.
The team says that could help people with read sensitive information while in public – for example, privately accessing their bank account balance at a cash machine.
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