Instead, the coil is pulled through the external magnetic field, which induces a voltage across it.

ECONOMIST: Weighing a kilogram

The coil is suspended in an external magnetic field and the current running through it adjusted so that the attraction between the two magnets balances the gravitational force on the suspended mass.

ECONOMIST: Weighing a kilogram

That is because the transmitter uses a large flat coil, placed over the heart, to generate the magnetic field that powers the receiver.

ECONOMIST: Case history