My work on the Levitate project includes an investigation of levitating particle displays, a novel type of display where content is composed from several levitating objects. A common vision for these displays is to create point-cloud representations of complex objects. Whilst these displays have a lot of interesting characteristics and have great potential for interaction (see this page for an overview), they do have some limitations.
I’ve been looking at alternative ways of using levitating particles to create interactive content. One way is to use levitating particles to turn static objects into interactive displays. The aim is to use the particles as actuated display elements, enabling the otherwise static objects to present dynamic and interactive content. The following video shows an example of this: a single levitating particle is animated to show an ascent of a range of mountains. My paper at Pervasive Displays 2019  explores the potential applications of this novel display concept.
Combining Levitation with Physical Objects
One challenging aspect of this concept is how to use acoustic levitation in the space surrounding other physical objects. We explore several possibilities and their technical challenges in our paper. One method I want to highlight here is the use of acoustically transparent materials. These are materials that sound waves can pass through, including steel mesh and acrylic felt.
We’ve used these materials to create a variety of physical objects that are compatible with acoustic levitation, including the models shown on this page. These models use steel mesh for support structures and acrylic felt for appearance. Because they are partially transparent to ultrasound, the models can be placed inside, or on top of, an acoustic levitation device. Polystyrene beads can then be levitated around them and used as actuated display elements.
Particles as Annotations
Levitating particles can be used as dynamic cursors for annotating an object: e.g., to highlight points of interest, to draw a user’s attention to a particular feature, or to add context to other sensory information. The particles annotate the object without affecting its appearance and without directly manipulating it. The annotation could be automated (e.g., a programmed series of movements to different locations) or interactive, responding to a user’s input.
Particles as User Representations
Levitating particles can be used as the active user representation in an interactive system: e.g., as a cursor directly controlled by the user or as a display element that gives feedback about the user’s actions (e.g., Point-and-Shake). The particle turns a static object into an interactive display, by providing an effective way of representing the user and the effects of their interactions with the system.
Particles as Animated Display Elements
Levitating particles can be used to animate static objects, by providing a dynamic visual element to the content. This could be used to enhance the appearance of an object to create a more engaging experience, or to illustrate events or behaviours that are difficult to convey statically.
In our Pervasive Displays 2019 paper , we explored the use of acoustic levitation to create dynamic displays from static physical objects. We presented three ways of using actuated particles to create new interactive experiences with these static objects: by annotating and drawing attention to their features; by adding an active user representation for interactivity; and by creating dynamic display components that enhance their appearance.
Whilst the particles are simple in appearance, their proximity to the other object and its features allow them to communicate rich information through their motions. Expressiveness is enhanced when these motions are linked to a user’s actions.
This research has received funding from the 🇪🇺 European Union’s Horizon 2020 research and innovation programme under grant agreement #737087. This work is supported by the University of Bristol and Universidad Publica de Navarra.
 Enhancing Physical Objects with Actuated Levitating Particles
E. Freeman, A. Marzo, P. B. Kourtelos, J. R. Williamson, and S. Brewster.
In Proceedings of the 8th ACM International Symposium on Pervasive Displays – PerDis ’19, Paper 24. 2019.