UltraBoard: Always-available Wearable Ultrasonic Mid-air Haptic Interface for Responsive and Robust VR Inputs

Free-hand interaction in VR is intuitive and easy to learn, making it applicable to fundamental interactions such as VR typing. However, the absence of haptic feedback reduces spatial awareness and immersion while performing the input, impacting accuracy and increasing fatigue. While previous works embedded haptic feedback, they either require constant contact with the skin or a desktop installation with a fixed distance. We propose Ultraboard, a novel wearable haptic interface providing ultrasonic mid-air haptic feedback for all hand regions, including fingertips. We adaptively control the phased array's position in accordance with the hand movement and location to support consistent haptic feedback for real-time VR typing input. With simulation and experiment, we designed and validated the customized ultrasound phased array to support hand input. We propose guidelines for the development of a finger-level wearable ultrasonic mid-air haptics interface and system through this process. A follow-up user study showed significant improvements in typing confidence and usability with Ultraboard. Notably, the mid-air tactile typo alert enabled with our interface enhances user experience during VR typing. Our results showed a promising approach to utilizing a mid-air haptic interface to promote confidence in VR typing.