Vacuum variable capacitor

A vacuum variable capacitor is a variable capacitor which uses a high vacuum as the dielectric instead of air or other insulating material. This allows for a higher voltage rating using a smaller total volume. There are several different designs in vacuum variables. The most common form is inter-meshed concentric cylinders, which are contained within a glass or ceramic vacuum envelope, similar to an electron tube. A metal bellows is used to maintain a vacuum seal while allowing positional control for the moving parts of the capacitor.