Dr Post's system uses magnets made of an alloy of neodymium (a rarish metal), iron and boron.

ECONOMIST: Maglev trains

Because some users turn the crank-handle faster and harder than others, a nifty three-stage gearbox and a dynamo based on powerful neodymium-iron-boron magnets is used to ensure that efficiency is largely independent of the torque applied.

ECONOMIST: MONITOR