Theoretical study of the overwrite spectra due to hard-transition effects [magnetic recording]

The impacts of the hard-transition position-shift effect and the hard-transition shape-change effect on the readback signal spectra in overwrite environment were studied theoretically. Starting from first principles, it is shown that in a typical overwrite situation, where a lower frequency CW (continuous wave) background pattern is overwritten by a higher frequency CW data pattern, the hard-transition effects produce sidebands that are centered around the even harmonics of the data frequency. The distances from the peaks of a sideband to the center of the sideband are given by the odd harmonics of the background frequency. It is shown that the amplitudes of the peaks in these sidebands are given by simple analytical expressions. The results of the theoretical work are verified by comparison with numerical simulations of the hard-transition shift effect and with experimental data. In both cases, good agreement is obtained