The original „donut“ loop antenna did not work seemingly due to a design issue. A scalpel, two tiny wires, and four solder joints rescued it.

This has made small antennas more popular, despite some limitations. [Tech Minds] reviews the GA-450 indoor active HF loop antenna and finds it better than expected. You can see the video review ...

Abstract: Control of objects using remotely generated magnetic fields has established itself as a viable ... subject to the limitations of Earnshaw's theorem, making stable, open-loop levitation ...