A number of experimental measurements of the Casimir force have observed a logarithmic distance variation of the voltage that minimizes electrostatic force between the plates in a sphere-plane geometry. We show that this variation can be simply under
stood from a geometric averaging of surface potential patches together with the Proximity Force Approximation.
The imperfect termination of static electric fields at semiconducting surfaces has been long known in solid state and transistor physics. We show that the imperfect shielding leads to an offset in the distance between two surfaces as determined by el
ectrostatic force measurements. The effect exists even in the case of good conductors (metals) albeit much reduced.
A new systematic correction for Casimir force measurements is proposed and applied to the results of an experiment that was performed more than a decade ago. This correction brings the experimental results into good agreement with the Drude model of
the metallic plates permittivity. The systematic is due to time-dependent fluctuations in the distance between the plates caused by mechanical vibrations or tilt, or position measurement uncertainty, and is similar to the correction for plate roughness.
