The Magnetic Configuration of Stylus Recording

A cylindrical magnetic stylus driven by a coil can be used to transfer bits of information onto a magnetic surface. These bits are recorded as round spots and combinations of these spots can form a desired pattern, e.g., numbers or letters. A mathematical model corresponding to the magnetic properties of a recorded spot is proposed and analyzed. The major considerations in the analysis are the field pattern existing about the spot, the self-demagnetization of the spot, and interference resulting from crowding the spots. Field mappings, obtained with a miniature Hall probe, were used to experimentally verify the proposed model. The experimental results show that the analytic model can predict the magnetic configuration of the spot at distances away from the recording surface that are considerably greater than the surface thickness. An alternate model is proposed for studying spot properties in regions quite close to the recording surface.