Rubbing noise generated by acoustic vibrations in ferrite test heads

Rubbing noise (RN) is an effect whereby acoustic waves generated by the friction between the head and the recording tape cause flux changes to circulate through the head, inducing a noise voltage over the windings of the head. T. Kimura et al. (1980) have demonstrated the correlation between RN peak frequencies and sample dimensions in special test heads made predominantly from polycrystalline MnZn ferrite. The present authors have expanded on the experiments by investigating similar test heads of single crystal material and identifying several distinct acoustic vibrational modes and corresponding propagation velocities. The most important features of the spectra are: (1) strong peaks appear in the RN spectra at certain frequencies; (2) as the tape velocity is increased, the amplitude of the RN increases, but the frequency distribution is unaltered; (3) when the yoke height is reduced by lapping, the peaks in the frequency spectra shift systematically to higher frequencies; (4) one longitudinal and two transverse velocities are required to explain the observed frequency shifts for yoke heights >340 μm; (5) for smaller yoke heights, modes of lower propagation velocities are found