Volumetric haptic display

A volumetric haptic display (VHD) is similar to a (visual) volumetric display, but informs touch instead of vision. A VHD projects a touch-based representation of a surface onto a 3D volumetric space. Users can feel the projected surface(s), usually with their hands. The display is otherwise not detectable, and offers no visual feedback. There are no known instances of a fully operational VHD at this time.

Technological implementation
The University of Bristol has developed a method for haptic feedback that could be integrated into a volumetric display. The system uses focused ultrasound to create a haptic object in mid air.

Feedback
The following feedback can be provided to the user:
 * Surface contact
 * Surface texture
 * Vibration
 * Motion-based/topological changes of surface