Brainwave-Controlled Zen Garden
makezine.com
makezine.com
All that is needed is just a plate of metal with a frame to stop the sand from spilling over and a sound wave generator that generates sounds based on your EEG.
The big bonus is that you can HEAR your own brain this way and by adding your own heartbeat as background music, you will instantly have an much better feeling and maybe even have an out of body experience. (It's shown in studies that the own heartbeat can help induce that)
That meta-material allows sound to pass through, which is perfect to reduce a loss of sensitivity in the visualization. Also you could use something other than sand, that reacts much more intense to any kind of resonance frequency. My idea would be to create lots of fullerenes, each containing elements with different resonance frequencies, mix them up and put them into a closed cage made out of that meta-material. Should be amazing to watch the material form shapes out of your brain waves.
(stumbled over this article, while researching for the material http://www.technologyreview.com/view/421285/mass-can-be-crea... maybe of interest)
If the plate is a circle, the vibrational nodes that you will see will 100% be circular and "totally boring". If, however, the shape is a rounded rectangle, you might see "something interesting", but that's cheating, because the the interesting shapes have to do with the fact that your plate is a rounded rectangle and not to do with the actual components of the sound that you're putting in.