On the bandwidth of magnetic record/Reproduce heads

The frequency dependent efficiency of a head is of vital importance in both the record and playback processes. The bandwidth of a head is defined as the frequency at which the efficiency has dropped by 3 dB. Based on measured permeability spectra incorporated into a boundary-integral-equation head model, it can be shown that bandwidth is a strong function of head geometry. Heads with geometries designed for improved d.c. efficiency also have much higher bandwidths. Bandwidth is also a strong function of the permeability spectrum of the head material. It appears that high frequency efficiency depends little upon d.c. permeability but mainly (through the gyromagnetic constant) upon the saturation magnetization of the head material.