A pinchable aerial virtual sphere by acoustic ultrasound stationary wave

In this paper, we propose a system to generate aerial virtual spheres which invokes tactile sensation and is omni-directionally pinchable. The acoustic radiation force of ultrasound stationary waves is known in the field of non-contact micro manipulation. This force applied to a small object in the stationary wave is in proportion to the gradient of the square of the acoustic pressure and directing from anti-node to node. We demonstrate a prototype system consisting of 996 transducers which generates a focal anti-node point at the center of the workspace. We performed the acoustic pressure distribution analysis and subjective experiments. As a result, it is discovered that the virtual sphere was sensed as the same size as theoretically expected.