Air capacitors are capacitors which use air as their dielectric. The simplest air capacitors are made of two conductive plates separated by an air gap. Air capacitors can be made in a variable or fixed capacitance form. Fixed capacitance air capacitors are rarely used since there are many other types with superior. The dielectric constant value of a material is a measure of the amount of electrical energy stored in a material for a given voltage. Since capacitors. Variable air gap capacitors are usually made of two groups of semicircular metal plates. One group is fixed, while the other can be rotated using a. Applications for variable capacitors are mostly constrained to AC circuits. Most applications demand high frequency, high power and low loss.