Here’s a cool project by Ivan Poupyrev, an interactive 3D surface called Lumen. Unlike a regular 3D display, which uses optical tricks to make the image appear to extend out from the screen, in this display the pixels actually move.
I’ve been wanting to make something like this for a long time, but couldn’t come up with a viable actuator to move the pixels. Solenoids would draw way too much current, and a robotic arm to push each one in turn would be too slow. Ivan’s solution, though, seems just right. Each pixel is activated by a wire made of shape memory alloy, which deforms when heated and returns to it’s original shape when cool. Aha!