  We developed a new aerial push-button with tactile feedback using focused
airborne ultrasound. This study has two significant novelties compared to past
related studies: 1) ultrasound emitters are equipped behind the user's finger
and reflected ultrasound emission that is focused just above the solid plane
placed under the finger presents tactile feedback to a finger pad, and 2)
tactile feedback is presented at two stages during pressing motion; at the time
of pushing the button and withdrawing the finger from it. The former has a
significant advantage in apparatus implementation in that the input surface of
the device can be composed of a generic thin plane including touch panels,
potentially capable of presenting input touch feedback only when the user
touches objects on the screen. We experimentally found that the two-stage
tactile presentation is much more effective in strengthening perceived tactile
stimulation and feeling of input completion when compared with a conventional
single-stage method. This study proposes a composition of an aerial push-button
in much more practical use than ever. The proposed system composition is
expected to be one of the simplest frameworks in the airborne ultrasound
tactile interface.
