Screenshot by Michelle Starr/CNET

There are lots of potential uses for mid-air haptics; gaming immediately springs to mind -- imagine if you could feel a physical ball while playing with the Kinect for instance. User interfaces for a variety of technologies would be another -- particularly if it was combined with holographic visuals, Iron Man-style. And there are some pretty interesting potential uses for medical technology -- such as being able to feel around inside a 3D model of a CT scan to touch a tumour, for example.

A new method of haptic feedback has been invented by a team of researchers at the University of Bristol's Department of Computer Science. Rather than puffs of air -- as developed by Disney Research -- it uses a technology usually used for imaging, for visualising the unseen: ultrasound.

Ultrasound produces an effect known as acoustic radiation force, which produces a physical effect -- the scattering and absorption of the acoustic wave. By observing how sound behaves when it hits an object, we can extrapolate the shape of that object.

It's also possible to focus complex patterns of ultrasound in such a way as to cause air disturbance. It is this property of ultrasound that the researchers have tapped to create 3D haptic shapes in mid-air -- users can feel those air disturbances on the skin. Moreover, those patterns can be formed into 3D shapes.

"This approach applies the principles of acoustic radiation force, whereby the non-linear effects of sound produce forces on the skin which are strong enough to generate tactile sensations. This mid-air haptic feedback eliminates the need for any attachment of actuators or contact with physical devices," the paper's abstract reads. "The user perceives a discernible haptic shape when the corresponding acoustic interference pattern is generated above a precisely controlled two-dimensional phased array of ultrasound transducers."

What this means is that an array of ultrasound generators creates a variety of shapes -- such as cubes and spheres -- which the user can feel when they place their hand above the array. By itself, of course, it can't be seen -- but the team has used a container of oil to show how the shapes work. In the video below, you can see the array directed at the oil, creating a variety of shapes. This is what the team means when they say the haptics can be "seen".

It wouldn't, of course, exist by itself, either: the team envisions its use in concert with a display, such as a holographic display -- if or when that technology arrives.

"Touchable holograms, immersive virtual reality that you can feel and complex touchable controls in free space, are all possible ways of using this system," said study leader Dr Ben Long.

"In the future, people could feel holograms of objects that would not otherwise be touchable, such as feeling the differences between materials in a CT scan or understanding the shapes of artefacts in a museum."

The full study, "Rendering volumetric haptic shapes in mid-air using ultrasound", can be found online in the journal ACM Transactions on Graphics.