But how to shut it off?

Researchers in Japan and Germany have converted energy from soundwaves into electromagnetic energy, trapping a magnetic “spin current” between metal layers. In the experiment, when sound waves are directed at an interface between the thin metal layer and magnetic material, electrical signals are generated at a pair of electrodes attached above. When the soundwaves reach the magnetic material, this creates a spin current that gets picked up by three layers of metal. This is where the exercise class-sounding reverse spin Hall effect kicks in, transforming it into an electrical voltage