Heater AC Voltage Induced Flying Height Modulations

For a thermal flying-height control (TFC) slider, its heater is usually provided with DC voltage. However, recently, both DC and AC voltages may be supplied to the heater. Unlike supplying AC voltage to the slider and disk in the past, the AC voltage to the heater will not only produce a thermal protrusion on the slider, but also leaves a part of the AC voltage on the slider/disk interface. The voltage acts as the electrostatic force and can be used for further control of the slider, even in the drive level. Simulations show that the flying height modulation is highly related to the AC frequency. By sweeping the AC frequencies while monitoring the flying height and pitch angle modulations, the first and second pitch modes of air bearing frequencies can be experimentally obtained without slider/disk contact. The roll mode frequency is also obtainable when the skew angle is not zero. The simulation results agree well with the experimental results obtained by a laser Doppler vibrometer (LDV). Therefore, the sweeping AC frequency method provides a practical scheme to obtain the air bearing frequencies without any slider/disk contact, even in the drive level.