This story was originally published in UCSB’s The Current.
Haptic holography promises to bring virtual reality to life, but a new study reveals a surprising physical obstacle that needs to be overcome.
A research team at UC Santa Barbara has discovered a new phenomenon underlying emerging holographic haptic displays that could lead to the creation of more compelling virtual reality experiences. The team’s findings are published in the journal Science Advances.
Yon Visell | Credit: Courtesy
Holographic haptic displays use phased arrays of ultrasonic emitters to focus ultrasound in the air, allowing users to touch, feel, and manipulate three-dimensional virtual objects in the air with their bare hands, without the need for a physical device or interface. While these displays show promise for use in various application areas, including augmented reality, virtual reality, and telepresence, the tactile sensations they currently convey are diffuse and faint, feeling like a “breeze” or “puff of air.”
“Our new research explains why such holograms feel much more diffuse or indistinct than expected,” said Yon Visell, an associate professor in UCSB’s College of Engineering, whose research focuses on interactive technologies with a focus on haptics, robotics and electronics.
The study, led by Visell and Gregory Reardon, a doctoral researcher, used high-resolution optical imaging, simulations and perceptual experiments to study ultrasound-excited waves excited in the skin during haptic holography. They discovered that holographic displays excite widespread vibration patterns – shear shock waves – in the skin.
The formation of shock waves creates a trailing wake pattern | Credit: Gregory Reardon
In haptic holography, Visell explained, shock waves are created when ultrasonic waves are focused and scanned in air, causing vibrations in the skin. These vibrations can interfere with each other in such a way that their strength is amplified in some places, a phenomenon known as constructive interference. The formation of shock waves creates a wake pattern that extends beyond the intended focus, reducing the spatial precision and clarity of tactile sensations. As an analogy, the researchers said, if the focused beam of sound is a fast-moving boat on the water, the shockwave pattern is a wake following the boat. Current holographic haptic displays stimulate shockwave patterns distributed in the skin in such a way that the sensations feel very diffuse.
“Our study shows how holographic haptic displays, which are a promising new technology for virtual reality and telepresence, require new knowledge about acoustic innovations in design,” said Visell. “By understanding the underlying physics of ultrasound-generated shear shock waves in the skin, we hope to improve the design of haptic holographic displays and make them more realistic and immersive for users. Such haptic displays could allow us to augment our physical environment with an infinite variety of virtual objects, interactive animated characters, or tangible tools that can not only be seen, but also touched and felt.”
The team’s discovery of the previously unknown shock wave phenomenon underlying haptic holography represents an important step forward in the development of haptic holographic displays that could allow users to interact more realistically and immersively with the future metaverse.
