Silver mica capacitors have been widely used as high-performance capacitors over the years. Mica is a group of natural minerals. Silver mica capacitors are capacitors which use mica as the dielectric. These are high precision, stable and reliable capacitors. They are available in small values and are mostly used at high frequencies and in cases where low losses (high Q) and low capacitor change over the time is desired. Although silver mica capacitors are not as widely used, these days, nevertheless they are still available and used in a variety of applications where their particular properties are needed.
Two main reason for the decline in the use of silver mica capacitors is their size, resulting from the materials used and their construction. The cost of silver mica capacitors is higher than many other types that can often be used these days. There are two types of mica capacitors: clamped mica capacitors and silver mica capacitors.
There are 2 distinct types of mica capacitor.
- Clamped Mica capacitors
These had even worse tolerance and stability than other clamped capacitors since the mica surface is not perfectly flat & smooth. References to mica capacitors from the 1920s always refers to this type.
- Silvered mica capacitors
Silvered mica capacitors are one of the less popularly used types due to their high cost. They are sometimes informally referred to as mica capacitors.
Silver mica capacitor applications
Silver mica capacitors are able to provide very high levels of accuracy, stability and low loss. As a result silver mica capacitors found many uses in particular for radio frequency applications:
RF oscillators: Silver mica capacitors can fund uses within RF oscillators. In these applications, their low loss levels enable the Q of the tuned circuit to be improved. This yields improved stability and lower phase noise levels. Also, their low-temperature coefficient enables even free running oscillators to achieve good stability levels and low drift.
Filters: The close tolerance levels of the silver mica capacitor enables the exact performance to be calculated and predicted. Also, the low loss levels of the silver mica capacitor enable high Q filters to be realized.
Coupling and decoupling: The cost of silver mica capacitors generally means that they are not used for coupling and decoupling, but they can withstand high voltages and this may have meant they have been sued in these applications occasionally.
Silver mica capacitors are not as widely used these days. Size and cost, along with improvements in other types of capacitors have meant they are not widely used. They are also not seen in surface mount formats.
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