It is very exciting to see something floating in the air or free space that is exactly what an anti-gravity project is about. The object (basically a small piece of paper or thermocol) is placed between two ultrasonic transducers which generate acoustic sound waves. The object floats in the air because of these waves which seem to be of anti-gravity. This is not only a cool looking Arduino levitation project, but it also has many practical applications.
[original story: Circuit Digest]