AC erase head for cassette recorder

A 70 dB erase ratio, the minimum practical for metal tapes, was obtained with ac erase magnetic heads of audio compact cassette recorders. Prerequisites for obtaining this level were the prevention of a "re-recording effect" and the selection of a gap configuration that would generate a highly efficient erase field. The relation between the erase effect and gap length has been clarified by the use of the finite element method; the number, depth, and length of the gaps have been determined. A practical design method for erase heads is also described.