The Real Area of Contact in Polymeric Magnetic Media—I: Critical Assessment of Experimental Techniques

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Abstract
A critical assessment of techniques used to measure the real area of contact has been conducted. The techniques that are found to be suitable to measure contact area between a polymeric magnetic medium and a mating hard surface are: electrical-contact resistance and two-beam optical interference. The limitation of the electrical-contact resistance is that both surfaces must be electrically conductive. This technique only provides semiquantitative information. The two-beam optical interference technique provides complete distribution of the asperity-contact areas. Limitations of this technique are that the mating member must be optically transparent and both surfaces must be smooth. A monochromatic light of wavelength 706 nm (red) and a glass slide of high refractive index (1.93) were found to be suitable for magnetic tapes under study. All measurement techniques suffer from overestimation of the real area of contact, especially in the case of smooth magnetic tapes. Calculations for overestimation of the real area of contact for typical magnetic tapes are presented.

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