Mica Capacitors
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Mica is a naturally occurring mineral that can be split into very thin, electrically insulating sheets. In modern silvered-mica capacitors, conductive silver is deposited onto mica layers to form the electrodes. The result is a stable, low-loss capacitor that performs very well at radio frequencies.
Why mica is useful
- Very good capacitance stability.
- Low dielectric loss.
- High Q in RF circuits.
- Low temperature coefficient in appropriate designs.
- Good high-voltage capability for their capacitance range.
Typical applications
Mica capacitors appear in tuned circuits, oscillators, RF filters, transmitters, instrumentation, and other places where capacitance must remain stable while signal frequency is high. They are less common for bulk energy storage because their capacitance values are usually much smaller than electrolytic values and their cost per farad is higher.
Q and dielectric loss
A high-Q capacitor loses relatively little energy each cycle. That is valuable in resonant circuits because excessive capacitor loss lowers circuit Q, broadens the resonance, and wastes signal energy as heat.
Mica versus ceramic
Modern C0G/NP0 ceramic capacitors can also provide excellent stability and low loss in small values. Mica remains useful when its combination of RF performance, voltage capability, stability, package style, or proven behavior fits the design better.
Selection checklist
- Capacitance and tolerance.
- Working voltage.
- Temperature coefficient and stability.
- RF current and loss requirements.
- Physical lead length and mounting, which affect high-frequency behavior.