A noncontact tactile stimulus can be presented by focusing airborne ultrasound on the human skin. Focused ultrasound has recently been reported to produce not only vibration but also static pressure sensation on the palm by modulating the sound pressure distribution at a low frequency. This finding expands the potential for tactile rendering in ultrasound haptics as static pressure sensation is perceived with a high spatial resolution. In this study, we verified that focused ultrasound can render a static pressure sensation associated with contact with a small convex surface on a finger pad. This static contact rendering enables noncontact tactile reproduction of a fine uneven surface using ultrasound. In the experiments, four ultrasound foci were simultaneously and circularly rotated on a finger pad at 5~Hz. When the orbit radius was 3~mm, vibration and focal movements were barely perceptible, and the stimulus was perceived as static pressure. Moreover, under the condition, the pressure sensation rendered a contact with a small convex surface with a radius of 2~mm. The perceived intensity of the static contact sensation was equivalent to a physical contact force of 0.24~N on average, which was 12 times the radiation force physically applied to the skin.

翻译：非接触式触觉刺激可通过将空中超声波聚焦于人体皮肤来实现。最近有研究报道，通过低频调制声压分布，聚焦超声不仅能在手掌上产生振动，还能产生静态压力感。这一发现拓展了超声触觉渲染的潜力，因为静态压力感的空间分辨率较高。本研究验证了聚焦超声可在指垫上渲染与小型凸面接触相关的静态压力感。这种静态接触渲染能够利用超声波无接触地再现精细的不均匀表面。实验中，四个超声焦点在指垫上以5赫兹的频率同时进行圆周旋转。当轨道半径为3毫米时，振动和焦点移动几乎不可察觉，刺激被感知为静态压力。此外，在该条件下，压力感渲染出与半径为2毫米的小型凸面的接触。静态接触感的感知强度在平均上等效于0.24牛顿的物理接触力，这是物理施加于皮肤的辐射力的12倍。