Mica capacitors

When you were a child, you might have seen mica, a naturally occurring, transparent substance that flakes off in thin sheets. This material makes an excellent dielectric for capacitors.
Mica capacitors can be made by alternately stacking metal sheets and layers of mica, or by applying silver ink to the sheets of mica. The metal sheets are wired together into two meshed sets, forming the two terminals of the capacitor. This scheme is shown in Fig. 1.

Fig. 1: Meshing of plates to increase capacitance.

Mica capacitors have low loss; that is, they waste very little power as heat, provided their voltage rating is not exceeded. Voltage ratings can be up to several thousand volts if thick sheets of mica are used. But mica capacitors tend to be large physically in proportion to their capacitance. The main application for mica capacitors is in radio receivers and transmitters. Their capacitances are a little lower than those of paper capacitors, ranging from a few tens of picofarads up to about 0.05 μF.