By using phased arrays of ultrasonic transducers, it is possible to levitate a small 1mm foam ball and move it around at speeds greater than 1m/s.  By moving the ball very quickly and leveraging the persistance of vision effect, this project can draw images in mid-air in a volume of 100x100x140mm.  RGB LEDs are used to illuminate the foam ball at various points in its path to create multi-color images.  4 FPGAs are used to convert a position into the phased signals needed to drive the transducers.  The FPGA can also rotate, translate and scale the images.  You can even create animations - see a video for an animation of a butterfly flapping its wings.  Kicad schematics and PCB layouts, FPGA code and simulator code are provided as well.
 
https://github.com/danfoisy/vdatp