Can We Increase the Perceived Intensity of Mid-Air Haptic Shapes Rendered With Dynamic Tactile Pointers?

Abstract

Ultrasound mid-air haptic (UMH) devices use an array of ultrasonic transducers to emit phase-offset acoustic waves in such a way as to focus them at precise locations above the device, referred to as focal points, generating localized vibrotactile stimuli when they encounter a user’s skin. Rendering mid-air vibrotactile shapes is a fundamental building block in many applications of ultrasound mid-air haptics. Recently, Hajas et al. introduced Dynamic Tactile Pointers (DTP) as an effective method for conveying clear shape information. By moving an amplitudemodulated (AM) focal point relatively slowly along a shape contour and marking pauses at vertices to highlight them, this method yields the best recorded shape identification performances for UMH to date. In particular, DTP renders much clearer shapes than the other standard approach to UMH shape rendering, Spatio-Temporal Modulation (STM). In this method, an unmodulated focal point is rapidly moved between neighboring positions. By controlling the frequency at which the focal point cyclically returns to any given position (the draw frequency), STM locally amplitude-modulates the pressure signal at each location along a traced contour, giving the sensation of a singular vibrotactile shape on the skin which is significantly more intense than shapes produced with AM. Adisadvantage of STMis that it produces rather blurry shapes which negatively impacts shape identification performances. Despite its benefits relative to STM, shapes rendered with DTP rely on amplitude modulation, causing them to feel much weaker than STM shapes. In this work, we propose to investigate Spatio-temporallymodulated Tactile Pointers (STP), a novel approach for reproducing the behavior of DTP using spatio-temporal instead of amplitude modulation, with the aim of improving the perceived intensity of tactile pointers.

Publication
IEEE World Haptics Conference (Work-in-Progress paper)