Tai-Chi (Tangible Acoustic Interfaces for Computer-Human Interaction), is a system developed by researchers from Switzerland, Italy, Germany, France and the UK that can turn just about anything into a control surface.

“We have made a system that can give any object, even a 3D one, a sense of touch,” says Ming Yang, an engineer at Cardiff University, UK, who is coordinating the project.

Two or more acoustic sensors are attached around the edges of the surface. These pinpoint the position of a finger, or another touching object, by tracking minute vibrations. This allows them to create a virtual touchpad, or keyboard, on any table or wall.

This video (WMV) shows the technology being used as a musical instrument control surface.

Tai-Chi uses tiny piezoelectric sensors to sense surface vibrations. The sensors are connected to a desktop computer loaded with software developed by the team and the system can track up to two objects at once, in one of two ways.

One method involves measuring differences in the amount of time vibrations take to arrive at two or three different sensors – a similar approach to sonar. Using this method any surface can be made touch sensitive simply by attaching the sensors.

The other method requires just one sensor and can actually be more accurate – to within just a few millimetres. But this method requires the calibration of the system beforehand, so that it recognises the vibrations caused by contact at different points on the surface. It then uses a database of vibration “fingerprints” to identify the point of contact.

“For little cost you can have a much larger touch-sensitive area,” says Yang. “The whole surface of your desk could become your keyboard and mouse-pad.”