Ultrasound midair haptics (UMH) can present non-contact tactile stimuli using focused ultrasound without restricting the user's movement. Recently, UMH has been shown to present not only conventional vibrotactile sensations but also static pressure sensations by locally rotating an ultrasound focus at several hertz. With these pressure and vibration sensations, UMH covers three mechanoreceptors on which tactile perception relies: SA-I, FA-I, and FA-II. This study proposes a texture rendering method in UMH based on these receptor characteristics. Three basic ultrasonic stimuli corresponding to each mechanoreceptor are designed, and tactile textures are rendered through their combinations. For SA-I, a pressure stimuli were employed. For FA-I and FA-II, vibration stimuli at 30 Hz and 150 Hz, respectively, are employed. 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. Its 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：超声空中触觉技术能够利用聚焦超声波呈现非接触式触觉刺激，且不限制用户运动。近期研究表明，该技术不仅能够呈现传统的振动触觉，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感。凭借这些压力与振动感觉，该技术覆盖了触觉感知所依赖的三种机械感受器：SA-I、FA-I和FA-II。本研究提出一种基于这些感受器特性的超声空中触觉纹理渲染方法。设计了分别对应三种机械感受器的基本超声刺激，并通过其组合实现触觉纹理渲染。针对SA-I感受器采用压力刺激，针对FA-I和FA-II感受器则分别采用30赫兹与150赫兹的振动刺激。实验结果表明，所提方法能够渲染至少六种具有不同粗糙度与摩擦感的可区分纹理。值得注意的是，通过与真实物理对象的对比，我们发现仅含压力的刺激被感知为滑腻而光滑，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，粗糙度水平可达100目砂纸程度。