What is a Mica Capacitor? Types and Applications

What is a mica capacitor?

The mica capacitor is an electrode plate made of metal foil or sprayed with silver layer on the mica sheet. The plate and mica are superimposed layer by layer, and then die-cast in glue powder or sealed in epoxy resin. It is characterized by small dielectric loss, large insulation resistance and small temperature coefficient, which is suitable for high-frequency circuits.

The earlier mica capacitors were composed of electrodes made of metal foil or silver sprayed on the surface of the mica sheet, and then laminated them according to the required capacity and then laminated in the rubber wood shell. At present, most of them are covered with a layer of silver electrode on the mica medium, and the core structure is stacked, and then packed into the shell to form a capacitor. The shell has Taojia shell, metal shell and plastic shell, which is commonly used as plastic shell.

Working principle of mica capacitor

The working principle of mica capacitors is to use the metal plates on both sides of mica to store the charge in the dielectric to form an electric field. In the process of charge storage, the dielectric constant of mica plays a key role. By controlling the thickness and area of mica, the capacity of the capacitor can be adjusted to achieve fine control of the charge.

When the capacitor is connected to the circuit, the electron flow will flow into the capacitor from the positive plate and out of the negative plate, which will form an electric field between the two plates of the capacitor. According to Coullen's law, the capacity between the two-pole plates of the capacitor is proportional to the distance between the electrodes and inversely proportional to the dielectric constant of the dielectric.


The role of mica capacitors in the circuit
1. Used for filtering circuits
In the circuit, the mica capacitor can be used as a capacitor in the filter circuit and used for high-frequency noise and clutter signals in the filter circuit, making the signal in the circuit more pure and stable.
2. Used for coupling circuits
Mica capacitors can also be used in coupling circuits. Coupling circuit is a method used to transmit signals from one circuit to another. The mica capacitor can be used in the coupling circuit to transmit the signal in the circuit, so as to realize the connection between different circuits.
3. Used for resonant circuits
Mica capacitors can also be used in resonant circuits. Resonant circuit is a circuit used to adjust the frequency in the circuit. The mica capacitor can be used in the resonant circuit and to adjust the frequency in the circuit, so as to realize the resonance of the circuit.

What are the two types of mica capacitor?

Mica capacitors can be divided into foil type and silver type. It is very direct to electroplate silver on mica sheets by vacuum evaporation or sintering. Due to the elimination of the air gap, the temperature coefficient is greatly reduced, and the capacitance stability is higher than that of the foil type.

In addition to the above two, capacitors with different structures depending on different methods of mica sheet fixation.
1. Zip-type pressed mica capacitor

The upper and lower layers of the core group are protective sheets, and the middle is the silver mica sheet and the lead-out foil staggered between each layer of mica pieces. The overlaided core group leads out the foil by bending, wraps and fixes the core group, and then installs the clamp outer leads at both ends, that is, the two electrodes of the capacitor, and finally seals the plywood shell.

2. Heart-shaped mica capacitor

There are kinds of heart-shaped mica capacitors such as button type, button monolithic type and so on. The electrode is drawn from the center and the outer circle, and finally a protective layer is added outside the core group.

3. Monolithic mica capacitor
The asymmetric electrode printed on both sides of the silver mica sheet is extended to the end surface, and the two end surfaces of the core group stack are led out by silver welding.

What are the advantages of mica capacitors?

1. High stability: Because the insulation performance of the mica film is very good, the mica capacitor has high stability. At high temperature, high voltage and high frequency, its capacitance value will hardly change.

2. High reliability: The structure of mica capacitors is simple and there is no electrolyte, so it is more reliable than electrolytic capacitors. The service life of mica capacitors is very long, which can reach more than several decades.

3. Low loss performance: The mica capacitor has a very low dielectric loss, which can ensure the transmission quality and stability of the signal. It is especially suitable for high-frequency circuits and microwave circuits.

4. High-temperature resistance: Mica capacitors have good high-temperature resistance and can work in high-temperature environments without melting or thermal decomposition. They are suitable for high-temperature circuits, aerospace circuits, etc.

5. Voltage resistance: Mica capacitors have high voltage resistance and can withstand high voltages. They are suitable for high-voltage circuits and high-voltage power supplies.

6. Cost control: The production cost of mica capacitors is relatively low and the processing process is simple, so that mica capacitors have a wide range of application prospects and can meet the needs of different fields.

7. Large capacity: The capacitance value of the mica capacitor can be very large, usually between a few nanometers and hundreds of micro methods. Compared with electrolytic capacitors, mica capacitors have a larger capacity.

What are the disadvantages of mica capacitors?

1. Large volume: Compared with some other capacitors, the device volume of the same capacitor is relatively large. This may limit its use in applications with limited space.

2. Relatively large weight: Due to the structure of the mica capacitor, its weight may be larger than some applications with high lightweight requirements.

3. Not suitable for high-frequency applications: the performance of mica capacitors in high-frequency applications is relatively poor, because its internal and dielectric characteristics may lead to high-frequency loss.

4. It is not easy to manufacture devices with high capacitance value: It is relatively complicated to manufacture mica capacitors with high capacitance value, so it may not be very practical in applications that require high capacitance values.

5. The price is relatively high.

What is equivalent to a mica capacitor?

Alternatives to mica capacitors include ceramic capacitors, paper dielectric capacitors, metalized paper dielectric capacitors, glass glaze capacitors, sealed capacitors, etc.

Ceramic capacitors: When the capacity and voltage resistance are the same and the volume is not limited, ceramic capacitors can replace mica capacitors.

Paper dielectric capacitors: under the condition that the capacity and voltage resistance are the same and the volume is not limited, the paper dielectric capacitor can replace the mica capacitor.

Metalized paper dielectric capacitors: under the same price and unlimited capacity, metalized paper dielectric capacitors can replace mica capacitors. In addition, metalized paper dielectric capacitors with equal voltage and equal capacity can also replace mica capacitors without considering the insulation resistance value and working frequency.

Glass glaze capacitors: metalized paper dielectric capacitors with the same capacity and pressure resistance can replace glass glaze capacitors without considering the influence of frequency.

Sealed capacitors: When the moisture-proof performance is not high, non-sealed capacitors with the same capacity and pressure can replace sealed capacitors.
The choice of these alternatives is mainly based on their physical characteristics, price and the needs of the application environment.

Do mica capacitors have polarity?

The mica capacitor is not polar. As a non-polar capacitor, it has great advantages compared with the general non-polar capacitor, which can be said to be the best of the non-polar capacitor.

Because mica capacitors are non-polar capacitors, unlike polar capacitors, they need to connect their positive and negative poles correctly. In mica capacitors, two metal foils play the same role in the electric field, so they can be regarded as the same polarity.

How do you read old mica capacitors?

The following are specific reading and measurement methods.
1. Using the bridge method to measure mica capacitance

Measuring mica capacitance by bridge method is a relatively common method. This method uses the principle of AC bridge to measure the capacitance by adjusting the size of the proportional resistance and adjusting the delay of the capacitor. Due to the characteristics of mica capacitors, this method can obtain relatively accurate measurement results.

2. Direct measurement of mica capacitance
The method of measuring mica capacitance by direct method is relatively simple. You only need to use capacitance metre or LCR metre. Although this method is simple and easy to practice, its measurement error is large, and you need to pay attention to the accuracy of calibrating capacitance metre or LCR metre.

The precautions for the measurement and reading of mica capacitors are as follows:
1. The mica capacitor needs to ensure the accuracy and stability of the test instrument when measuring.
2. It is necessary to pay attention to the polarity of the mica capacitor. This capacitor is divided into positive and negative poles. If the reverse polarisation is connected, the measurement results will be meaningless.
3. When measuring mica capacitors, it needs to be classified. The capacitance value and accuracy of mica capacitors produced by different models and different manufacturers will vary. Therefore, it is very important to choose the appropriate measurement range and the appropriate measurement method.
4. Before measurement, it is necessary to ensure that the test environment is static and vibration-free. When measuring, it is necessary to avoid hand-held measuring instruments or unstable operation, which will also affect the accuracy of measurement results.

Where are mica capacitors used?

Mica capacitors have been widely used in many fields due to their unique performance. The following are common application areas of mica capacitors:

Electronic equipment
Mica capacitors are widely used in various electronic equipment, such as computers, communication equipment, TV, audio equipment, etc. Its high-temperature stability and low loss make the mica capacitor perform well in high-frequency circuits and signal processing.

Automotive electronics

Mica capacitors play an important role in automotive electronic systems, such as engine control units (ECUs), electric drive systems, lighting and entertainment equipment, etc. Because mica capacitors have high-temperature stability and reliability, they can adapt to extreme conditions such as high temperature and vibration in the automotive environment.

Power electronics

In the field of power electronics, mica capacitors are often used in DC filters, frequency converters, circuit breakers, power supplies and other equipment. Its low loss, high voltage and high temperature stability make mica capacitors an ideal choice in the field of power electronics.

Military spaceflight

Due to its excellent insulation performance and high temperature stability, mica capacitors are also widely used in military and aerospace fields. Mica capacitors are used in key military and aerospace equipment such as radar, navigation systems, satellite communications and aircraft to ensure the reliable operation of the system.

New energy field
With the development of new energy technology, mica capacitors have been applied in the fields of solar panels, wind power generation systems and electric vehicle charging piles. Mica capacitors can provide efficient and stable energy storage and transmission, supporting the reliability and efficiency of new energy equipment.

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