Ultrasound midair haptics (UMH) can present non-contact tactile stimuli using focused ultrasound without any wearables. Recently, UMH has been shown to present not only conventional vibration stimulus but also static pressure stimulus by locally rotating an ultrasound focus at several hertz. Current UMH can present three basic tactile stimuli: static pressure, 30 Hz vibration, and 150 Hz vibration. These primarily elicit responses from three distinct types of mechanoreceptors: SA-I, FA-I, and FA-II. As human texture perception relies on the combination of mechanoreceptor neural responses, this study proposes combining the three basic stimuli to render tactile texture in UMH. Experimental results demonstrate that the proposed method can render at least six discriminable textures with different roughness and friction sensations. Notably, through comparisons with real physical objects, we found that the pressure-only stimulus was perceived as slippery and smooth. The smoothness was similar to a glass marble. When vibration stimuli were synthesized, the perceived roughness and friction increased significantly. The roughness level reached that of a 100-grit sandpaper.

翻译：超声空中触觉技术（UMH）能够利用聚焦超声波呈现非接触式触觉刺激，无需任何可穿戴设备。近期研究表明，UMH不仅能够呈现传统的振动刺激，还能通过以数赫兹频率局部旋转超声焦点来呈现静态压力刺激。当前UMH可呈现三种基本触觉刺激：静态压力、30 Hz振动与150 Hz振动。这些刺激主要分别激发三类不同的机械感受器：SA-I型、FA-I型与FA-II型。鉴于人类的纹理感知依赖于机械感受器神经响应的组合，本研究提出通过组合这三种基本刺激来实现UMH中的触觉纹理渲染。实验结果表明，所提出的方法能够渲染至少六种可区分的纹理，这些纹理具有不同的粗糙度与摩擦感。值得注意的是，通过与真实物理对象的对比，我们发现仅使用压力刺激时，感知效果为滑腻而光滑，其光滑度类似于玻璃弹珠。当合成振动刺激时，感知到的粗糙度与摩擦力显著增加，其粗糙度水平可达100目砂纸的程度。