Haptic design tutorial: Using the circle sensation

To be an effective and well-designed haptic feedback, the sensation does not have to be complex. Rather it must convey the key information required at the right time. The key here is understanding how the haptic parameters for each circle sensation are altered in response to user interaction.

Here, we discuss some of the basic parameters of a circle sensation and how they relate to haptic design in some of our use cases. These points are applicable, whether you are using the Sensation Editor, writing your own using our API, or using the Ultrahaptics Core Asset for Unity.

	Intensity   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.
	Circle Radius   The size of the circle felt on the hand. The SDK and the Ultrahaptics Core Asset (UCA) use metres as the units of the radius. A recommended radius of 0.02m will give a circle covering the average palm.
	Draw Frequency   This is the number of times the circle is drawn on the hand 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.
	Haptic Switching Duration   For a sequence of multiple haptic events, this is the duration (in seconds) between consecutive haptic events, during which no haptics are emitted. When switching between haptics leaving a delay in haptic playback of at least 0.02 seconds is advisable. This makes the recognition of the change in haptics more discernible. Use the timeline feature in the UCA to implement the haptic switching duration. You can read more about Haptic Switching Duration in our tutorial on Designing Effective Mid-Air Haptics.
	Playing Duration   This is the amount of time a haptic sensation is played for.

Mid-air push-button

Ultrahaptics technology can be used to extend control interfaces by providing the end-user with a sense of touch in mid-air. As an example, the circle sensation can be used to create a mid-air button. Ultrahaptics created its home controls application to demonstrate how touch-less, mid-air haptic feedback can be used in a smart home of the future. This can then be configured to control elements of the home such as lights, heating, etc.

Figure 1. An example of how the sense of touch in mid-air can extend control interfaces in a smart home context.

Interaction with the circle sensation

In our example, the circle sensation is fixed in space and represents a button that is pushed to turn the lights on and off.

1. While watching TV, the user places their hand over the array and feels the presence of the control box, while a visual representation appears on the screen.
2. They move their hand over the button and feel the button presence haptic, which controls the lights in the room.
3. They can move their hand over a slider to control hifi volume in the room.

During the operation of the button, the circle sensation’s parameters change, as described below:

Figure 2. Parameters of the circle sensation for the mid-air button.

1. User puts their hand over the array. The controls appear and the user feels a subtle ‘presence’ haptic sensation.
2. User moves their hand towards the location of the button and places their hand over the button, feeling a circle sensation with the parameters shown in the image.
3. User pushes their hand downwards.
4. The button is pushed fully. The user feels a stronger, impulsive burst of the Circle to mimic the real pushing down of a button. The gap in the haptic feedback is referred to as the haptic switching duration and the click of a button.
5. User moves their hand upwards and feels a second stronger, impulsive burst of the Circle to mimic the real feeling of releasing a button.

Mid-air video controls

Ultrahaptics technology can also be used to enhance feedback for virtual control scenarios. This example shows a virtual video-control interface, where the user can pause, play, fast-forward or rewind content.

Figure 3. An example of how the sense of touch in mid-air can extend control interfaces.

Interaction with the circle sensation

The user puts their hand over the array and feels a circle sensation, while seeing their hand position represented by a circle cursor. They move their hand over the fast-forward or rewind icons on the screen to change the video playing. They can also play or pause the video with a tapping gesture.

There are three key interactions which have two different circle haptic designs:

1. User puts their hand over the array and feels a circle sensation, their hand is represented by a circle cursor.
2. User pauses the video by using a tap gesture (Figure 4 below).

Figure 4. Tap gesture as shown in the Sensation Editor

3. User moves the hand to fast-forward or rewind icon: haptic is a tracked circle sensation, congruent in speed, size, rotation and shape (Figure 5). You can read more about congruency in our article on Designing effective mid-air haptics.

Figure 5. The haptic and the visual representation of the fast-forward button. Note congruency between haptic and visual. 

“Ultrabean” interactive advertising

The “Ultrabean” interactive advertising poster demonstrates how a brand can use haptic technology to encourage brand engagement, creating compelling interaction. Here, a consumer will see the poster in a public space and see a bean on the screen. They use their hands to “grind” a virtual coffee bean, feeling the sensation of grinding coffee as they move their hand through it. When they have completely finished grinding the bean, the coffee brand is revealed.

Figure 6. The user grinds a virtual coffee bean with the hand.

Interaction with the circle sensation

The circle sensation in this demo is emitted each time a piece of the fractured bean collides with the hand. Since multiple fragments of the fractured bean will collide with the hand very quickly, the sensation should feel like points that are felt for a very short amount of time on different parts of the hand.

Each time the piece of fractured bean collides with the hand, the user feels a circle with the following parameters:

Figure 7. The haptic parameters of the circle sensation representing fragments of the virtual coffee bean.

“Beyond Terra” interactive film poster

Beyond Terra, our interactive, Sci-Fi film poster concept, is another demonstration of the power of mid-air haptics to create compelling interaction and brand recognition. 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 8. Gameplay of Beyond Terra, the user’s hand becomes the space ship and warps from a static movie poster to an interactive experience.

Interaction with the circle sensation

An expanding circle sensation, sequenced with the hand-scan (based on a line sensation ) at the beginning of the experience, indicates warping into space and starting the game. The user places their hand over the array and feels the sensation on their palm whilst seeing the visuals warp into the space game.

Figure 9. The expanding circle sensation.

Figure 10. Parameters of the circle sensation.

You can read more about best practice for haptic design in our other articles in this series.