Tactile feedback in mid-air ultrasound haptics with adjustable spatial resolution

초록

This research presents a novel beamforming method for mid-air ultrasound haptic devices, targeting a key limitation in existing technologies-the inability to dynamically adjust the size of the acoustic focal area. This constraint directly impacts spatial resolution and limits the design flexibility of haptic feedback. As interest in human-machine interaction grows, mid-air ultrasound haptics has emerged as a promising solution; however, conventional approaches such as delay-and-sum (DAS) beamforming offer minimal adaptability without hardware changes. To address this challenge, we propose a beamforming algorithm based on the energy difference method (EDM), which enables software-controlled modulation of the focal area by optimizing the phase and amplitude of individual transducer channels. The proposed method was validated through both acoustic simulations using an analytical model and experimental measurements using a custom-built 8-by-8, 40-kHz ultrasonic array with transducer-level phase compensation. Results demonstrated that the focal area could be adjusted by approximately 25-30% across various focal positions, showing strong agreement between simulations and experiments. Furthermore, the modulated acoustic radiation force was visualized using a thin (20 mu m) polymer film, confirming the spatial resolution adjustability. This capability enables either precise tactile localization or stronger radiation force, significantly enhancing the versatility and application potential of mid-air haptic systems in next-generation human-machine interfaces.

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