Use of readback signal modulation to measure head/disk spacing variations in magnetic disk files

-A new method is developed for measuring the dynamics of the head/disk interface in magnetic disk files. This method utilizes the modulation of a sinusoidal readback signal that results from head/ disk spacing variation. Measurements of slider dynamics using this readback signal modulation (RSM) technique are compared with measurements made with the laser-Doppler vibrometer (LDV) for transient slider motions that are introduced by several different means of slider disturbance. The RSM measurements are calibrated experimentally by use of the LDV together with the functional form provided by the Wallace equation, which expresses the dependence of the readback voltage on various recording parameters including the head/disk spacing. The RSM technique for head/disk spacing measurement variation has a resolution of 50 nm without correction, and this can be improved to 5 nm by removal of the systematic error that is associated with the recorded signal. A frequency range of 20 Hz to 100 kHz is achievable. Since the read/write head of the disk file is used as the measurement transducer without modification, and relatively simple and inexpensive additional instrumentation is required for the implementation of the RSM technique, it is expected that this method may become a useful tool in the research and development of magnetic disk files.