Wouldn't it be more accurate to call this an acoustic suspension beam? Calling it a tractor beam implies that it can be mounted on the ceiling and pull an object off the floor. Hence the name (at)tractor beam.
Well yes and no, traction is the act of "tirer" in French, that is the act of pulling. So a farm tractor is named as such because it pulls some (usually plowing) equipment behind it, and a tractor beam because it pulls some stuff at a distance.
Also reminds me of an interesting lesson we had in flying school, where our CFI was explaining that the "propeller" on an airplane should really be called a "tractor" because it is technically pulling the aircraft along, whereas an actual "propeller" would push the aircraft along (much as a ship's propeller does at the stern).
Sometimes talking about cars someone brings that up the other way around - rear wheels 'propel', the commonly used 'traction' is about the front wheels pulling the car ...
Whenever you see "tractor beam" in this context, it most likely refers to "tractor beams" from Star Trek, which are all about pulling stuff towards you.
I've only read the posted article, but it seems theoretically possible to move objects, perhaps needing more speakers. For that, shift to a different modulation that sets the trap slightly to the side, at each small step.
Analogous to a stepper motor.
I think the idea here is that suspension is easy (fans are enough for that), and the tricky part is pulling from "backwards", which this system does as indicated by the last few seconds of video.
