It's the interaction between particles that makes this reversal of polarity possible. Figure 2: The vortex diode, in which the direction of the net motion depends on the density of magnetic-flux ...

But if you reverse polarity, that oxide layer breaks down and current flows. To [Hales] this sounded like it could also act as a diode and so he went to work doing plenty of experiments and ...

You want to make sure that a battery plugged in the wrong way, or a polarity mistake with your bench PSU doesn’t damage that hardware. It’s easy enough to plop in a diode for protection ...