Using a conductive capacitor that is integrated as part of the pen, it connects to an electromagnetic field generated by an excitation coil in the digitizer.

ENGADGET: N-trig's Digital Pencil plays pen and fingertip roles, claims mastery of both

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