Tractor beams are real, and you can make one at home
While the term “tractor beam” is most commonly associated with films featuring aliens lifting cows out of fields, they really exist, and you can make one out of common electronics for under $75 (R1 022).
More specifically, you can make an “acoustic tractor beam”. These machines use sound waves to attract a small object and hold it in place. The tractor beam seen here uses an array of speakers controlled by an Arduino Nano.
The speakers output a 40 kHz frequency that can hold a small object, usually demonstrated with a circular ball of piece of candy a few millimetres apart. This works as the speakers are constructed to create a “quiet region” in the middle of the device. All around this region the speakers generate noise. If the ball or piece of candy tries to leave the quiet region, it is pushed back by this distortion in the air.
If you have a head for research papers, you can read the one behind this invention. Even better is the fact that one of the researchers on the project, Asier Marzo from Bristol University, will show you how to make one.
You can find the full written tutorial on Instructables; it includes a shopping list of all the common parts as well as links to buy them, proving that there’s no expensive, bespoke tech hidden in there somewhere. It also includes the code needed for the Arduino to run the speakers correctly, which is obviously an important part of the project.
You can see more of the tractor beam in action below by professor Bruce Drinkwater, also from Bristol University. The professor explains the principles behind the device as well as dashing some of our hopes. Firstly, it could be scaled up to lift a person, but they would be deafened by the noise and probably cooked by the resulting heat. In addition: no speakers exist that could produce a sound loud enough to pull it off.