Abstract: A process and apparatus for the non-destructive measurement of the thickness of sheets or hollow bodies made of dielectric materials, such as plactis, makes use of a microwave frequency signal which is fed to an elongated microwave strip line which is placed either close to, or in contact with, the material to be measured, whereby the change in the propagation time of the signal represents the thickness, or the filling factor of the measured material. In the case of hollow bodies the strength of the signal is insufficient to be affected by the wall of the body remote from the conductor, and an advantage of the system is that it can be used to measure plastic materials while in a plastic state while in the process of extrusion.

Abstract: The invention concerns a method for measuring the thickness of very thin, electrically conducting films of the order of 1 to 1000 nanometers and measuring apparatus for performing the method. The thickness of the electrically conducting films is measured by means of high-frequency electromagnetic waves in the microwave range by use of the surface resistance and consideration of the conductivity of the film as a measure of the film thickness. The thickness determination makes use of the reflection factor and/or the transmission factor of the microwave on the conductive film. This can be done with the aid of two antennas in free space in the far field of these antenna arrangements or, if the antennas are designed as waveguide flanges, it can also be done in the near field, in which case the waveguide flanges are arranged opposite each other at a very small distance.