DIY tractor beam

[Xlucine]

As said on tin:
http://www.instructables.com/id/Acoustic-Tractor-Beam/
It's a good excuse to get yourself an oscilloscope

[Peter Parker]

Two-in-one sonic levitator and high-powered dog whistle! Amaze your friends with the ability to make small plastic beads hover whilst summoning every dog within 10 miles!