When designing interactive experiences with Ultrahaptics, an important area to consider is the design of the mid-air haptic sensation. Whilst mid-air haptics is relatively new in the field of interface design, this series aims to make the process easier by explaining some haptic parameters and how they can be used. This article focuses on a simple line sensation and how it can be changed to generate distinctly different sensations for different applications.
Here are some basic parameters of a line sensation:
Related to the strength of the sensation felt.
This parameter varies from 0 to 1. Note that this control is non-linear: aim for 1 as much as possible. Varying the intensity can convey the feeling of resistance.
The size of the line drawn on the hand.
The SDK and the Ultrahaptics Core Asset (UCA) use metres as the units. A typical line length could be 10 cm, or the width of the hand. This will depend on your application.
This is the number of times the line is drawn per second. Time Point Streaming (TPS) only.
User studies have found that a low draw frequency, such as around 20 Hz can suggest bumps and roughness, whereas a high draw frequency, around 100 Hz, can feel smoother.
The “Forcefield” demonstrates how our haptic technology can be used to create a virtual forcefield or boundary. As the hand moves through the vertical plane of the forcefield, a sensation is felt across the fingers and palms.
Figure 1. The forcefield in use.
This sensation can be used to represent haptic boundaries and is therefore widely applicable. For example, when the hand passes a boundary between a haptic object such as a cube. It can also be applied in control scenarios where the user moves their hand through the forcefield (in either the x or y-axis), controlling some other component in the application.
Figure 2. The forcefield sensation representing the haptic boundaries of a 3D object.
Interaction with the line sensation to make the Forcefield
The Forcefield sensation is formed by calculating the line segment intersection of the hand (modelled as a plane) and a “forcefield beam” (shown here as a vertical plane). When the user’s hand passes through the forcefield beam, the line haptic segment is positioned in the region of intersection, giving the experience of interacting with a virtual forcefield.
Figure 3. Parameters of the line sensation
By making the line movement dynamic, so that it dances around the hand, we can create the sensation of magic powers and electrical energy. We call this the “Lightning” sensation. At Ultrahaptics, we have used this sensation for two different use-cases:
“The Sorcerer” is an interactive movie poster concept, where users interact with the magic powers of the Sorcerer by placing their hands in a crystal ball. Adding the sense of touch when interacting with the character boosts brand engagement when compared to the same, non-tactile experience.
The Lightning sensation is also used in our “Magic Spells” VR experience. While guided by the spells book, the user places their hand in the orb and conjures spells, each time feeling the “magic” energy enter and then emit from their fingertips (Figure 5). This sensation, combined with the auditory and visual cues adds to the feeling of presence and and reality.
Figure 5. “Lightning” sensation as used in the Ultrahaptics Magic Spells VR experience.
Interaction with the line sensation to make Lightning
In The Sorcerer interactive poster, the user places a hand in the interaction zone and instantly feels a tingling, buzzing sensation, emulating the Sorcerer’s powers (Figure 4).
In the Magic Spells VR game, the user clasps both of their hands around an orb and feels the Lightning sensation, absorbing the magical energy as the orb shrinks (Figure 5a). The user then points their hand at objects, releasing their newly gained magic power, feeling sensation traveling through their hands and out of their fingertips (Figure 5b).
To create the Lightning haptic, a line sensation is projected between the centre of the palm and to the tips of each finger, dwelling for a short period before jumping to the next random finger (Figure 6).
Figure 6. Parameters of the line sensation.
The line length is defined by points on the hand. The movement of the line is defined by the Jump Period, which sets the amount of time spent on each finger. You can experiment with this parameter for different sensations and applications. The Sorcerer and Magic Spells use a period of 0.1s, giving a jump frequency of 10 times a second.
The hand-scan is designed to convey the sensation of being scanned by a biometric scanning device. It can be used in applications in gaming or real-world interface. It is effective at confirming that an action has been completed in a control interface.
We use the hand-scan sensation in our interactive, Sci-fi movie poster “Beyond Terra”. When the user places their hand in the interaction zone, the scene warps from movie poster to shoot-em-up style arcade game. The user takes control of the spacecraft, firing lasers and dodging alien spacecraft and asteroids.
Figure 7. The gameplay and interaction of the Beyond Terra interactive poster – the hand controls a space ship and the user must avoid being hit by enemy fire and asteroids.
Interaction with the line sensation to make the Hand-scan
The hand-scan is used in the ‘space warp’ sequence at the start of the experience as the static poster changes to the interactive game. A line is projected horizontally across the hand, then travelling from the wrist to the finger tips (Figure 8).
Figure 8. Parameters of the line sensation.
We define Scan duration as the time it takes for the line to travel from the wrist to the fingertips. In Beyond Terra this is approximately one second. A lower scan duration results in faster scanning speed. For your application, you may wish to repeat the scanning sensation, even varying the scanning duration.
In our Sci-fi poster, once the hand-scan completes the haptic changes to an expanding circle, enhancing the feeling of warping into space. A haptic switching duration, in which a detectable gap is felt, is used when changing between haptic sensations. This switching duration ensures that the second haptic sensation is discernible.
You can read more about best practice for haptic design in our other articles in this series.