Mica is a mineral that can be readily sliced into thin chips, makes an excellent dielectric and is used in capacitance incorporated in circuits requiring stable and accurate capacitors with low losses and high leakage resistance. Mica sheets are brittle and cannot be rolled up like a paper dielectric. The capacitor consists either of alternate layers of metallic foils, with mica forming a stack which is then hermetically sealed in some hard plastic or alternatively the mica can be silvered stacked and enclosed in a plastic moulding. The main characteristics of this type of capacitor are low power factor, high voltage operation and long term stability at room temperature. Precision mica capacitors, used as sub-standards Can be adjusted to better than 0.01 percent stability for values over 1μf. They are sealed in cases to protect against moisture. The silvered mica plate capacitor has a better temperature coefficient when compared to the stacked plate type. Both types exhibit slight non-cyclic capacitance shifts during temperature variation yielding a nonlinear temperature capacitance characteristics.

Specifications

Capacitance range                                    1pf to few micro farad

Ratings                                                    up to 2000V

Temperature                                             55⁰C to 125⁰C

Dielectric constant                                     8

Power factor                                             approx 0.0003 at 1 MHz

Applications: They are used in filter circuits and tuning circuits.