Magnetic fields surrounding recording wires

THERE are certain applications for magnetic recording that require the storage of information in the form of coded pulses in magnetic media such as wire or tape. To conserve space, it is necessary to record the greatest number of pulses in each linear inch of the medium that is possible without the pulses losing distinctness or objectionably blending with the preceding or succeeding pulses. Studies of the magnetizing current, pulse width, and frequency as related to this blending have been made, using wire as the recording medium. During the studies it became evident that useful information could be obtained if the size of the pulses as recorded on the wire could be directly determined. A wire retaining magnetically recorded pulses is similar to a succession of short cylindrical magnets laid in a line and connected end to end by a permeable medium. Therefore, if the magnetic field surrounding these minute magnets could be mapped and the pattern photographed, the distance between the magnetic poles could be determined easily. As is well known from elementary physics, iron filings when scattered about a magnet are not only attracted to the magnet but also arrange themselves in definite lines that apparently begin and end at the so-called poles of the magnet. These lines of iron filings are said to “map” the magnetic field. In a similar way, the magnetic field of extremely small magnets can be mapped if the iron particles are sufficiently small and proper techniques are used in producing the patterns.