As discussed in our introduction to how Ultrahaptics works, Ultrahaptics uses focused ultrasound to transmit sensation to the surface of the skin. These focused points are referred to as Control Points. Since the surface of the skin is not particularly sensitive to a fixed control point it must be modulated, either by changing its position or intensity in a way the skin is sensitive to.
When the control point position is moved fast enough to stimulate the skin surface, we use the term Spatiotemporal Modulation. You can see the concept in the diagram below.
When changing its intensity, we are amplitude modulating the control point (a).
When changing its position we are using Spatiotemporal Modulation (b).
What is Spatiotemporal Modulation?
The main idea is simple: instead of turning the ultrasound on and off, the focal point moves across the hand fast enough to stimulate the sensitive mechanoreceptors in the skin. The term Spatiotemporal Modulation (or STM) tells us that the ultrasonic waves are modulated both in space and time.
Unlike with our Amplitude Modulation API, mid-air haptic technology using Spatiotemporal Modulation is not limited to discrete focal points. Instead, lines and curves can be repeated almost continuously. These can then be used as a basis to render virtual objects and shapes, enabling a whole new spectrum of high fidelity applications in augmented reality (AR) and virtual reality (VR).
Projecting ultrasound onto an oil bath allows you to ‘see’ the shapes created by Ultrahaptics’ haptic technology and the difference between Amplitude Modulation and Spatiotemporal Modulation.
Here you can see the discrete focal points created by Amplitude Modulation:
Here you can see how Spatiotemporal Modulation enables you to render shapes:
What is Time Point Streaming?
Time Point Streaming (TPS) is an advanced mode of operation, available on the STRATOS platform and the Evaluation Kit (UHEV1).
With the Time Point Streaming API, Spatiotemporal Modulation is possible. Both the position and intensity can be continuously changed at a much higher rate than with our Amplitude Modulation API. Haptics are updated using a high-frequency callback function, streaming sensation at up to 40 kHz to the array.
Time Point Streaming offers advantages over our first-generation Amplitude Modulation API:
- Intensity modulation with multiple, individual frequencies and full control of transitions
- High-frequency updates, lower latency
- Smoother and quieter movement
- Generate sensation with less energy
- Complex sensations, shapes and surfaces for AR and VR applications.
You can read more about the Time Point Streaming API, and full details can be found in the documentation included in Ultrahaptics SDK.
NB: Spatiotemporal Modulation is not supported by the TOUCH Development Kit (UHDK5).