• Midair Haptics by Airborne Ultrasound Tactile Display (AUTD)
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  • Midair Haptics by Airborne Ultrasound Tactile Display (AUTD)

AUTD_960_600 The hardware and software of the device used in our laboratory are available at the following sites.
– Hardware: Currently available only in Japan. See Japanese page.
– Software (Open source)
– Q&A
– Paper about AUTD (IEEE Trans. on Haptics)
*If you have any questions on the software, please refer to the above Q&A. Please do not directly contact our laboratory or the above manufacturers.

The Airborne Ultrasound Tactile Display (AUTD) produces tactile sensation remotely on a human skin surface. The AUTD does not require users to wear any devices on them.

Ultrasound transducers arrayed on the AUTD surface generate a ultrasound focus at an arbitrary position in the air. At the focal point with high energy density, static pressure called “acoustic radiation pressure” is produced, and it can push the skin surface. The focal position can be electrically controlled based on the phase array technique. In addition to creating a focus, you can produce a more general complex pressure pattern by solving an inverse problem in real-time.

The current limitations of the technology are that the maximum pressure is about 50 mN per square centimeter and that the spatial resolution is comparable to the sound wave length 8.5 mm for 40 kHz ultrasound.  But under these constraints, radiation pressure pattern are controlled freely by a computer, which create various tactile sensations on the skin.

Haptics using such non-contact haptic feedback is called “midair haptics.” The initial studies of ultrasonic midair haptics were conducted by Hiroyuki Shinoda’s group from 2008 at the University of Tokyo. The research group demonstrated the basic technologies and haptic effects in the first half of the 2010s. Currently, the field is growing and many universities and companies in the world are moving forward with development.


World-first demonstrations by Univ. of Tokyo

Airborne Ultrasound Tactile Display (AUTD)  (youtube video SIGGRAPH 2008 E-tech)

The world first study of midair haptics (haptic feedback using ultrasound).

Touchable Holography (youtube video SIGGRAPH 2009 E-tech)

The first demo of midair haptic feedback synchronized with visual floating images.

Tactile Projector  (youtube video IEEE WHC 2013)fireworks_hand

Projecting visual image on the skin with midair haptic stimulation. A large aperture AUTD synchronizing multiple AUTD-units enabled this system.  

Haptomime, Mid-Air Haptic Touch Panel  (youtube video)

Floating touch-panel with midair haptic feedback.

3D Haptic Hologram (youtube video SIGGRAPH 2014 E-tech,  WHC 2015)

— Computational design of 3D acoustic energy-density field. 
The world first demo of static 3D haptic images. They could touch and perceive a static 3D shape haptically by their fingers and hands.

— Advanced scheme of acoustic hologram and application to levitation. Boundary hologram provides acoustic field that produces proper restoring force to any minute displacement and rotation of the object.
The algorithm enabled the world first ultrasonic levitation of a macroscopic non-spherical object significantly larger than the wavelength. It is applicable to arbitrary-shape objects considering the diffraction and reflection by the object.

Haptoclone (Haptic & Optical Clone) (Special page, youtube video SIGGRAPH 2015 E-tech)

Symmetric mutual telexistence by 3D haptic & optical field reconstruction. A pair of people can touch the realistic 3D image of each other with haptic sensation. 

Recent important results by Univ. of Tokyo

Producing Static Pressure Sensation

The generated ultrasonic radiation pressure is not very high. If a time-invariant pressure (static pressure) is applied to the skin, the stimulus does not exceed the tactile threshold and cannot be felt by humans. Therefore, the conventional aerial tactile presentation uses time-varying vibrotactile stimuli. However, it is felt as “vibration,” which is different from the sensation of touching an object in a usual way.
However, recent research by Morisaki et al. has revealed that a dynamic pressure distribution can create a sensation similar to static pressure. This finding has shown that a versatile tactile presentation is possible under a certain limitation on the spatial resolution and the maximum force.

Cooling SensationDisplaying cooling spot

Temperature is an important factor in tactile perception. However, non-contact presentation of temperature, especially cold sensation, has been considered difficult. However, Nakajima et al. recently confirmed that the skin temperature rapidly decreases due to the heat of vaporization when ultrasound waves are focused on the skin in a room-temperature mist of water. A temperature drop of 3 K was observed within 0.5 s immediately after ultrasound irradiation, comparable to cooling using standard Peltier devices. They also confirmed the movement of the cooling spot could be perceived.

Visualization of Ultrasound

A problem with midair haptics was the measurement of the sound field distribution. The virtually only practical way to measure the distribution was to scan a microphone with an automatic stage or robot arm. In 2021, Onishi et al. discovered a new practical method to measure the details of the sound field of intense ultrasonic waves. Using a thermo-camera, the sound pressure distribution on an arbitrary two-dimensional plane in a 3D space can be measured. The measurement is real-time and with high spatial resolution. For example, a thermal image of a mesh screen inserted in an ultrasonic wave can visualize the two-dimensional ultrasonic field distribution on the mesh in real-time. It is easy to obtain the 3D distribution by moving the screen. It is also possible to visualize the sound field distribution on a skin surface.

Other main results by Univ. of Tokyo

Lateral Modulation: A Method to Intensify Haptic Sensation by Ultrasound

Reciprocating motion of a focus along the skin surface (Lateral modulation, LM) can generate stronger sensation than Amplitude Modulation (AM) where the radiation pressure changes vibrationally at a spatially fixed point. The threshold of the radiation force of LM is 10 dB less than that of AM in the displayed maximum force, and LM can create haptic sensation on a hairy skin as well as a glabrous skin. 

Reducing Unnecessary SoundNoise

Quick phase change (as seen in LM) causes unexpected amplitude change. The amplitude change produces unexpected tactile perception and sound noises. The following shows a practical effective method to reduce it. (The sound generation and amplitude change by phase shift was first pointed out by Hoshi in 2016.)

3D Object Manipulation by Fingers

We are clarifying what information is essential to make the user feel the substance of a virtual object. Connected AUTDs surrounding fingers can generate a 5 mm diameter force spot, and create fine pressure distribution on the fingers. The distribution is controlled in real-time reflecting the contact state between the fingers and the virtual object. We have examined experimentally if the fingers can handle an object blindly. 

Motion Guidance

Haptic Pursuit
In human vision, smooth pursuit eye movement is the basic ability to visually follow a moving object by keeping it at the sight center. In this study, we validated that a human hand has a similar ability to track a midair haptic stimulus, i.e., a human palm exposed to a point vibration by AUTD can follow the continuous movement of the stimulation point. The ability of motion tracking by hand can be applied to haptic guidance.

Virtual Handrail
There is another strategy where the user find and follow the designated path actively. Consider a situation the path, from start to finish (the ‘goal’), is presented by scanning ultrasound focal points along the path. The scanned focal point produces vibrotactile stimuli on the hand, and users perceive the local path-direction easily. Then user can follow the path without strong concentration.

— Guidance along a palm

— Guidance perpendicular to a palm