I recall there being an article on how to build a levitation device using sound waves emitted by an array of Piezo transducers.
The thing I'm interested in is the standing wave phenomena created with sound waves. The standing waves have peaks and troughs where sound exists and doesn't exist. Kind of like stationary sound packets. It's probably the troughs where the levitation phenomena occurs.
I think this also ties into electromagnetic phenomena too. Bifilar coils with opposing currents don't exhibit this phenomena. The magnetic fields cancel. But I haven't investigated any effects using variable frequencies through the bifilar wires. And experimenters have noticed weird effects from caduceus coils. For instance I was measuring voltage drops across components in my HDR and discovered that the caduceus coil had no voltage drop at all.