Spatio-Temporal Modulation

A rendering technique used in mid-air ultrasound haptics in which a single focal point is moved rapidly along a closed trajectory (commonly circular) while its intensity is modulated over time. When the trajectory is swept fast enough (typically tens to hundreds of Hz), the skin integrates the moving point into a continuous shape or texture sensation. STM supports higher-fidelity rendering of surfaces, fur-like textures, and biological rhythms such as breathing, and is a core building block for using ultrasound haptics as an expressive non-visual output channel.