Tunable Spatial Resolution for Mid-Air Haptic Feedback via Energy-Based Focal Control

초록

This study presents a novel method for achieving controllable spatial resolution in mid-air ultrasonic haptic systems. Mid-air haptics have attracted increasing attention as an innovative human-machine interaction technology, as they enable tactile sensations in free space without physical media. However, in conventional array transducers, the focal area is primarily dictated by the operating frequency, leaving little flexibility for adaptation without hardware modification. Research on controllable spatial resolution through algorithmic approaches has been rarely found. To overcome this limitation, we investigate an energy-based beamforming algorithm, Energy-Difference-Maximization (EDM), that dynamically adjusts the focal area by optimizing source filter coefficients to maximize the acoustic energy difference between target and off-target regions. A custom 8×8 ultrasonic array (40 kHz) was developed in-house to validate the method. Experimental results confirmed that EDM enables tunable focal areas with approximately ±30% variation compared to the conventional Delay-and-Sum (DAS) method, while still maintaining sufficient acoustic pressure for tactile perception. This capability of algorithm-driven spatial resolution control offers new opportunities for mid-air haptic interfaces. By flexibly switching between sharp, localized tactile sensations and enhanced radiation force, EDM provides a versatile platform for adaptive and user-centered haptic feedback, broadening the applicability of ultrasonic haptics in interactive technologies. © 2025 IEEE.

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