Paradox of deep gap field and far field at high frequencies in a recording head

Recording heads made of complex permeability materials produce a deep gap field which may have an amplitude loss and a phase distortion with respect to the driving current. Simple Karlquist field equations indicate that the ratio of the far head field to the deep gap field is only a function of geometric dimensions. However, in the flux loop measurement of a ferrite VCR head, the far field does not follow the deep gap field at high frequencies. Analysis of head field equations shows that an equivalent surface current resulting from the complex head permeability can account for this paradox. The use of a flux loop to characterize the head transfer function in a magnetic recording channel is also discussed