Ultrasound can produce a felt sensation in mid-air
Aliases: ultrasonic haptics · mid-air haptics · acoustic radiation pressure
What it is
Ultrasonic haptics focus sound waves to exert pressure on the skin, letting a hand feel a "point" without touching anything. It moves feedback into the air so gesture and touchless interaction can also receive a tactile response.
Why it happens
Transducers focus acoustic waves at a point in space, and acoustic radiation pressure at the focus varies with the modulation signal, felt by skin as faint vibration. Moving the focus quickly while modulating amplitude lets the system trace virtual shapes or emit pulses. Feasibility rests on two conditions: enough energy density at the focus, and a hand positioned within it. Those conditions also create the limits—outside the focus there is almost no perceptible strength, and different hand postures present differently oriented skin, changing the sensation.
Studying it
Map the perceptible field: sample a spatial grid around the focus and record where users detect vibration and how strongly, yielding the effective working volume. Variables include focus position, modulation frequency, array parameters, and hand posture. Outcomes include detection threshold, intensity rating, and localization accuracy. Report distance and angle, since perceived strength is highly sensitive to both.
Where it stops holding
Current perceptible strength is far below contact-based feedback, so mid-air haptics suit light taps, contours, and cues, not force or resistance. The effective workspace is small and the hand must stay inside it or feedback disappears. Ambient noise, power draw, and the safety envelope for prolonged high-intensity ultrasound are all practical constraints.
Applying it
- Use mid-air haptics for light cues and contour tracing, not for force or resistance.
- Indicate the effective region so users know where the hand must stay.
- Prepare a fallback for leaving the region, such as an on-screen cue, rather than failing silently.
- Verification: measure the perceptible region and intensity distribution within the device's working volume, confirm feedback exists for common hand postures, and mark the boundaries that need indicating.
Related
- Within the group: D3.06.2 Perceptible strength is far below contact-based feedback · D3.06.3 Coverage is tightly coupled to hand posture
- Adjacent: C4.06.1 Mid-air gestures lack tactile feedback · N2.04 Missing feedback in spatial interaction
- Search terms:
ultrasonic haptics·mid-air haptics·acoustic radiation pressure