The development of haptic systems for telepresence, teleoperation, and virtual reality has long been focused on creating devices that enable users to interact with virtual three-dimensional (3D) items or surroundings floating in midair without any physical objects. By concentrating ultrasound output from phased arrays of transducers, emerging 3D holographic haptic displays can provide such tactile feedback in midair. The skin is deformed by nonlinear acoustic radiation pressures caused by incident ultrasound.

Shock wave creation produces a trailing wake pattern that extends beyond the intended focus point, reducing the spatial accuracy and clarity of tactile impressions. According to the researchers, if the concentrated sound beam represents a fast-moving boat on the water, the shock wave pattern represents a wake trailing the ship. Modern holographic haptic displays generate shock wave patterns in the skin that are so dispersed that the sensations seem highly diffuse.

Visell said, “Our study reveals how holographic haptic displays, which are a promising new technology for virtual reality and telepresence, require new knowledge in acoustics innovations in design. 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 enable us to augment our physical surroundings with a limitless variety of virtual objects, interactive animated characters, or graspable tools that can be not only seen but also touched and felt with the hands.”