Brian Kappus –
Ben Long –
Ultrahaptics Ltd.
The West Wing, Glass Wharf
Bristol, BS2 0EL, United Kingdom

Popular version of paper 3aEAa4 “Spatiotemporal modulation for mid-air haptic feedback from an ultrasonic phased array” presented Wednesday morning, May 9, 2017, 9 AM, Greenway D 175th ASA Meeting, Minneapolis

ultrasonic wavesHaptic feedback is the use of the sense of touch in computing and interface design to communicate with a user. The average person most often experiences haptic feedback when interfacing with modern mobile devices. These uses are relatively basic: a buzz to alert the user to an incoming call or a vibration when using a touchscreen keyboard.

Interfaces enabled by gesture recognition and virtual/augmented reality, however, typically lack haptic feedback. In this paper, we present “virtual touch” technology developed at Ultrahaptics. It enables the generation of haptic feedback in mid-air, on a user’s bare hands, by the efficient creation and manipulation of ultrasonic waves (i.e. frequencies beyond the range of human hearing).

There are a variety of mechanical receptors present on the hand that are sensitive to different types of sensation including temperature, static pressure, and vibration [1]. Receptors sensitive to vibration can be stimulated through focused acoustic pressure. Ultrahaptics’ technology uses ultrasonic transducers coupled with phase delays so that the resulting interference patterns create focused acoustic pressure at focal points. The pressure is sufficient to create tactile sensations without generating audible sound.

Because the vibration-sensitive receptors on the hand are not capable of perceiving ultrasonic frequencies, to create tactile sensations the acoustic pressure then needs to be switched off and back on again (modulated) at lower frequencies – around the range of 40-400Hz.

Previous versions of this technology have been limited to discrete points of acoustic pressure which are turned on and off at the necessary frequencies to create a tactile effect [2] [3] [4]. However, another way to create the tactile effect is to move the focal point back and forth, its movement away and back again providing the modulation at a frequency perceptible by the receptors. While it is away, pressure at the starting point is low. It then returns to the starting (high) pressure when it returns. From the perspective of this starting point, the acoustic pressure varies in amplitude. This creates tactile sensations.

The technique is called spatiotemporal modulation and using it a closed curve can be repeated almost continuously, forming a robust area of stimulation instead of discrete points. Advantages of spatiotemporal modulation include the ability to render an infinite variety of curves and volumes.

Previously, spatiotemporal modulation was impractical due to the hardware computing requirements. In this paper, we present algorithms developed at Ultrahaptics that realize the required acoustic fields with a fraction of the computing power. This enables fast update rates on reasonable hardware and opens up a new class of haptics.

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Caption: Oil-bath visualization of spatiotemporal modulation creating 3 simultaneous shapes. Acoustic pressure is able to deform the surface of a liquid and is used to visualize the acoustic field using edge lightning. In this example, 3 shapes are traced 200 times per second to create continuous lines of pressure.

[1] S. J. Lederman and R. L. Klatzky, “Haptic perception: A tutorial,” Attention Perception & Psychophysics, vol. 71, no. 7, pp. 1439-1459, 2009.
[2] T. Iwamoto, M. Tatezono and H. Shinoda, “Non-contact Method for Producing Tactile Sensation Using Airborne Ultrasound,” EuroHaptics, LNCS 5024, 504-513, 2008.
[3] T. Carter, S.A. Seah, B.Long, B. Drinkwater, S. Subramanian, UltraHaptics: Multi-PointMid-AirHaptic Feedback for Touch Surfaces, Proceedings of the 26th annual ACM symposium on User interface software and technology. (UIST ’13), New York, NY, USA, 8–11 October (2013).
[4] B. Long, S. A. Seah, T. Carter and S. Subramanian, “Rendering Volumetric Haptic Shapes in Mid-Air Using Ultrasound,” Transactions on Graphics (Proceedings of SIGGRAPH Asia) 33 (6) 181 (2014).

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