Many important engineering structures are often coated in a protective paint layer of some kind. This is not simply to improve the appearance of the structure but also to prevent corrosion and damage. There is some interest from industry to be able to track the solidification or drying of the paint layer as it happens to ensure correct thickness and material properties. One way to do this would be to measure the changing values of the permittivity of the paint layer as it dried.

An engineer initially decides to set up an experiment to try this idea out. He decides to use a large metal plate or substrate as one electrode, then paint it and then place another electrode (with a smaller area) directly on top of the paint layer. (The parallel plate equation is still a good approximation using the smallest value for A).

1) Describe how a dielectric material responds to an alternating electric field.

2) Describe how the permittivity might change with time for a polymer material like the paint as it dries and explain how this measurement could be used to find when the paint was totally dry.

3) Describe two flaws with this initial experimental set-up.

4) Briefly (half a page max) describe a commercial system of measuring permittivity including all appropriate references.