The impedance of magnetic recording heads at high frequencies is reduced by making the gap spacer of conducting material, because eddy currents in this conductor lower the permeance of the gap region. The traditional formulae for the complex permeability vs frequency of a conducting lamination (as used in transformer design) apply within the gap area. The formulae involve spacer initial permeability, resistivity and the gap depth which corresponds to the usually-used lamination thickness. Measurements of impedance vs frequency of a large -model- head verify the theory.
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