Contactless Measurement of Dielectric Thickness
Original Publication Date: 1979-Jun-01
Included in the Prior Art Database: 2005-Feb-20
If the dielectric permittivity of a sheet of dielectric material is sufficiently constant, over the surface of interest, the thickness of the sheet may be accurately determined by perturbing the capacitance of a pair of air capacitor plates with the dielectric sheet, e.g., by using a Blumlein Ratio Bridge technique. The technique is capable of measuring very small capacitive changes, approximately 10/-6/ pF, and is very insensitive to the effects of stray capacitance to ground. Using the design of Fig. 1, it is possible to observe variations in thickness of less than 1% in dielectric material. For example, 3 mil MYLAR* sheet, 14 inches wide, was measured, without touching, over the whole surface, with 0.3 inch x 0.3 inch area resolution.