Effects of Air Compression Between Parallel Plates in Interferometric and Capacitive Displacement Transducers

Abstract

When one of two adjacent surfaces of a displacement transducer, such as a parallel plate capacitor or an optical interferometer, is moved towards the other the compression of air between the surfaces alters the dielectric constant and the refractive index of the air during the motion. In making a precise measurement of a transient displacement with one or other transducer not in vacuo, a correction to the measured value of capacitance or path difference may be necessary.