Since yesterday was optical sensor day, today can be acoustic sensor day. It's also a neat idea, though at the moment I think optical sensors are in the lead, since there are already optical systems that can track an arbitrary number of points, and it sounds like acoustic sensors haven't reached that point yet. Hopefully the acoustic sensors can catch up in that respect. It sounds like acoustic sensors could be used on a much wider range of materials than optical sensors. Ultimately, I don't really care whether it's optical or acoustic, as long as I can get a large multi-touch panel someday soon.
http://www.newscientisttech.com/ar…http://www.taichi.cf.ac.uk/files/S…http://www.taichi.cf.ac.uk/files/P…http://www.taichi.cf.ac.uk/files/d…"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."