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Research Papers: Magnetic Storage

Heater AC Voltage Induced Flying Height Modulations

[+] Author and Article Information
Kyaw Sett Myo

Data Storage Institute,
(A*STAR) Agency for Science, Technology and
Research,
Singapore 117608

Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received March 22, 2013; final manuscript received September 6, 2013; published online November 18, 2013. Assoc. Editor: Frank Talke.

J. Tribol 136(1), 011901 (Nov 18, 2013) (7 pages) Paper No: TRIB-13-1069; doi: 10.1115/1.4025603 History: Received March 22, 2013; Revised September 06, 2013

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.

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Figures

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Fig. 1

The capacitances and voltages of the slider/disk system. When both the DC and AC are supplied to the heater, a part of the AC will appear between the slider and the disk. Here, V0 is the tribo-voltage between the slider and the disk.

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Fig. 2

Pemto slider for the simulation and experiment. The red dot at the bottom left represents the laser beam cast position.

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Fig. 3

The air bearing pressure profile of the slider when the thermal protrusion is 29 nm. The simulation is based on the unstructured triangular mesh. (a) Isometric view of the air bearing pressure and (b) top view of the air bearing pressure.

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Fig. 4

The 2D disk waviness used for the simulation

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Fig. 5

The slider flying attitude when no AC is on the slider/disk interface. (a) Head flying height versus time, (b) pitch angle versus time, and (c) roll angle versus time.

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Fig. 6

The slider flying attitude when the AC frequency is 100 KHz. (a) Head flying height versus time, (b) pitch angle versus time, and (c) roll angle versus time.

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Fig. 7

The slider flying attitude when the AC frequency is 280 KHz. (a) Head flying height versus time, (b) pitch angle versus time, and (c) roll angle versus time.

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Fig. 8

The SDs of the flying attitude versus the AC frequency at a radius of 25 mm and a skew angle of 0 deg. (a) Head flying height SD, (b) pitch angle SD, and (c) roll angle SD.

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Fig. 9

FFT of the pitch angle versus time for different AC frequencies. (a) When no AC is supplied, (b) when the AC frequency is 100 KHz, and (c) when the AC frequency is 280 KHz.

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Fig. 10

The FFT on the roll angle response after the slider is excited. The excitation conditions are: slider vertical speed = −5 mm/s (toward disk), pitch angle speed = 5 rad/s, and roll angle speed = 5 rad/s.

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Fig. 11

FFT power spectrum of slider vibration measured by LDV. Different electric power is supplied to the heater such that the slider can fly at three different states: just before contact, mild contact, and heavy contact.

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Fig. 12

The SDs of the flying attitude versus the AC frequency at a radius of 33 mm and a skew angle of 15 deg. (a) Head flying height SD, (b) pitch angle SD, and (c) roll angle SD.

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