Use of magnetic forces to control distance in a surface force apparatus

Abstract

A simple system that permits the surface separation to be varied smoothly and accurately in a surface force apparatus is described. It is based on the deflection of the force-measuring spring in a magnetic field gradient created by a current passing through two coils. The resulting displacement of the surface is highly linear with applied current and free of hysteresis over separations of 10 mu m or more. This allows the accurate measurement of the force between two surfaces by monitoring the difference between expected and observed spring deflection (using, for example, multiple-beam interferometry).