Expressive, Scalable, Mid-air Haptics with Synthetic Jets

Most haptic technologies require direct contact with a user's body, such that an actuator can deliver energy to the skin (e.g., vibration from a motor, heat from a peltier junction). The most successful commercial uses of haptics have been when actuators can be integrated into commonplace devices, such as smartwatches, phones, and gaming controllers. When special-purpose haptic devices are required to instrument the user, there are often aesthetic, social, setup time, and ergonomic costs. For this reason, haptic gloves, exoskeletons, vests, and similar worn accessories have seen comparatively little consumer uptake. 

"Mid-air" haptic technologies aim to lessen this burden by avoiding user instrumentation. Instead, haptic effects are rendered onto a user's body in a non-contact manner, most often using air as the energy-transmitting medium. All electronics and actuators are instead built into a host appliance, such as a public kiosk, automobile, or medical device. Mid-air haptic approaches are also particularly valuable in cases where the hands are dirty (e.g., cooking) or where germ transmission is especially problematic (e.g., surgery). For these reasons, mid-air haptics is an active area of research in human-computer interaction. However, at present, there are only a handful of mid-air actuation approaches in the literature, with varying strengths and weaknesses. Thus, it is desirable to continue to expand the set of technologies and approaches to better explore and unlock the potential of mid-air haptics.

In this vein, we explore an emerging haptic approach built around synthetic jets (or "synjets") – simple devices capable of generating a zero-net-mass-flux jet of air. These types of jets were recently proposed and initially characterized for haptic feedback applications by Shultz and Harrison. We expand on this prior work by demonstrating new device functionality, providing three new quantitative and qualitative evaluations, and showcasing how synthetic jet-based devices can create expressive haptic computing interfaces.

We have found that haptic synjets have numerous attractive properties. First and foremost, their output is highly controllable, allowing for rich haptic expressivity. Not only can we modify basic parameters such as windspeed, peak pressure, and jet diameter, but the air flows can also be dynamically modulated and steered to create temporal and spatial effects. Second, range and impact forces of synjets can be large, offering more salient haptics when compared to similar techniques. Third, synjets are highly scalable, from centimeter-scale to meter-scale devices; to demonstrate, we created a series of example devices across this size spectrum, with jet diameters ranging from 1.5mm to 125mm. In the case of our smallest synjets, power consumption is similarly diminutive (172mW), opening the door for inclusion in battery-powered devices such as VR headsets. And finally, synjets are relatively inexpensive – the actuators used in our demo devices range in cost between $2 and $89 USD, and would cost much less with economies of scale. 

Research Team: Vivian Shen, Chris Harrison, and Craig Shultz

Citation

Vivian Shen, Chris Harrison, and Craig Shultz. 2024. Expressive, Scalable, Mid-air Haptics with Synthetic Jets. ACM Trans. Comput.-Hum. Interact. 31, 2, Article 14 (April 2024), 28 pages. https://doi.org/10.1145/3635150