ERASING
The field associated with ac biasing signal does not cause any residual magnetism in a tape passing through the field. If the tape is unmagnetised when the signal is applied, then it will be unmagnetised when it is passing through the field.
If the amplitude of the ac signal is sufficient to saturate the tape, then even if the tape is not unmagnetised originally, it will be so when it has travelled through the field. This fact is used in the erase heads of most magnetic recording equipment. The tape is drawn through a strong local magnetic field arising from a high-frequency alternating current in the erase head. As each point of the tape travels into the field, it is saturated, and as each point recedes, it is subjected to a field strength ...
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