Variable Friction

A surface haptics technique that dynamically adjusts the friction between a user's fingertip and a touchscreen surface to create the sensation of different textures. Typically achieved through ultrasonic vibration that creates a thin cushion of air beneath the fingertip, reducing friction and producing a slippery feeling. By rapidly switching between high and low friction states as a finger moves across the screen, the system can simulate edges, bumps, and textures. For accessibility, variable friction enables blind and low-vision users to feel the boundaries and identities of interface elements without relying on audio feedback.