What is a mica capacitor?

December 17, 2010 | tags | views
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Mica, a mineral, is one of the oldest dielectric materials used in capacitor construction. There are several kinds of mica, with differing properties, but mica is in general very stable electrically, mechanically, and chemically. It has a dielectric constant in the range 5–7. Mica has the interesting property that its crystalline structure is asymmetrical. The binding forces in one plane are quite strong, while the binding forces along the perpendicular plane are very weak. Because of this, it has a distinct layered structure, and it is possible to split or cleave mica into very thin, optically flat, sheets. For capacitors, mica sheets in the range 0.025–0.125 mm or even thinner are used.

Mica capacitors are available with values that range from 1–4700 pF and even up to 1 μF, but they are generally thought of as low value capacitors. Rated voltages are in the range 100–1000 V for standard dipped mica capacitors. Rated voltages for RF transmitting capacitors are up to 10 kV. Given the excellent electrical performance of mica capacitors in general, manufacturers typically market them with close tolerances (1% or better).

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