Influence of surface roughness on the capacitive measurement of film thickness in elastohydrodynamic contacts

Film thickness is elastohydrodynamic lubrication is often measured by determining the capacitance between the mating surfaces and then calculating the film thickness from the measurements. Although this method gives a very high degree of accuracy if smooth surfaces are involved, it can lead to large errors for surfaces having a roughness which is approaching the mean film thickness. In this paper a simple model was constructed to qualitatively estimate the discrepancy.