2-18 Theory of Operation
Writing Data
To write data to the magnetic material on a card, it is necessary to create a
magnetic field near the stripe. This aligns all of the magnetic particles nearby in
the same orientation (polarity). The Magnetic Write Head contains a small coil of
wire wrapped around a semicircular iron core
4
. (The head coil and iron core are
used to focus and concentrate the magnetic field.) When electrical current passes
through the head coil, a small but concentrated magnetic field is generated across
the open ends of the core. The magnetic stripe on the card is magnetized with the
opposite magnetic polarity from the head. This is shown in the image below.
To change the polarity of the magnetic stripe under the magnetic head, the
polarity of the current in the head coil is reversed. This reverses the magnetic
polarity of the iron core, which in turn reverses the polarity of the magnetic
stripe.
4 Other materials may also be used for magnetic cores.
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