Pulse asymmetries and write nonlinearities in the write equalization process for magnetic tape recording

In this paper, we compare experimental measurements of magnetic tape recording signals with the results of simulation. Specifically, nonlinearities associated with the write equalization process are examined. It is found that the depth dependent vector Preisach model (VPM) of the magnetic recording process is able to semi-quantitatively reproduce nonlinearities that are seen in the readback from real heads and media. The failure of standard linear superposition models even qualitatively to capture these effects is demonstrated. Furthermore, the VPM shows, through the recorded magnetisation distribution, that demagnetizing effects from the data transitions can distort the write equalization pulses, if the pulses follow the data transitions too closely. This leads to a directional asymmetry in the writing process, such that symmetrically placed write equalization pulses do not lead to the most symmetrical waveforms.