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Circuits to Measure in Situ Head/Disk Surface Potential Differences and the Effect on a Slider Debris Accumulation

IP.com Disclosure Number: IPCOM000036528D
Original Publication Date: 1989-Oct-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 2 page(s) / 30K

Publishing Venue

IBM

Related People

Galwey, RK: AUTHOR [+3]

Abstract

Disclosed is a circuit to be used to measure the potential difference between the surface of a slider bearing and the surface of a magnetic recording disk, provided one is conductive. Changes in this potential offer a sensitive measure of material changes. The circuit nulls out the field between these surfaces. Thus, any harmful effects of this field, as for example, debris collection on the slider enhanced by electrostatic forces, are eliminated.

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Circuits to Measure in Situ Head/Disk Surface Potential Differences and the Effect on a Slider Debris Accumulation

Disclosed is a circuit to be used to measure the potential difference between the surface of a slider bearing and the surface of a magnetic recording disk, provided one is conductive. Changes in this potential offer a sensitive measure of material changes. The circuit nulls out the field between these surfaces. Thus, any harmful effects of this field, as for example, debris collection on the slider enhanced by electrostatic forces, are eliminated.

Typically, different materials are used for sliders and disks. There are often work function differences between those surfaces. Thus, any relative motion induces a displacement charge of q(t)= Cv= (eAV)/h(t), as shown in the figure.

The total charge Q measured with an additional bias voltage V and additional charge due to contact charging (triboelectricity) QT is Q= C(v + V) + QT. By using an independent measurement of the capacitance C and filtering Q and C appropriately, the circuit synchronously detects the component of the total charge synchronous with C. This signal is proportional to (v + V) and provides an error to servo the bias voltage V so as to null out the synchronous charge and the potential difference (v) is easily determined.

The circuit effectively nulls out the electrostatic potential between the head and disk surface. Experiments using low flying sliders flying on specially prepared disks...