Capacitors are an important passif element in electronic components, which are used to store charge and convert electrical energy into other forms, such as magnetic, mechanical or thermal energy. Capacitive element belongs to the electric field element, because its basic principle is to use the electric field to attract and repel the charge, so each capacitor must have at least two electrodes, and there must be a certain dielectric isolation between the two electrodes. Capacitors are widely used in electronic circuits. They are used in a wide variety of power filters, couplers, tuned circuits, oscillators, filters, noise reduction filters, amplifiers, isolators, transformers, DC-DC converters and other applications. In RF circuits, capacitors are used to couple electromagnetic waves into conductors, segment and isolate circuits, and adjust the frequency response of circuits. There are many types of capacitors and they can be classified according to their properties such as structure, dielectric material, dielectric thickness, rated voltage and capacity. Common types of capacitors include electrolytic capacitors, ceramic capacitors, organic capacitors, polyimide capacitors, metallized polyimide capacitors, thin film capacitors, longitudinal electrolytic capacitors, ferroelectric capacitors, tubular capacitors, infiltrating capacitors, and independent capacitors. The basic principle of capacitance depends on the storage capacity of electric charge. The amount of charge stored by it is closely related to the electric field intensity and plate spacing between the two plates of the capacitor, and is proportional to the plate area. The capacity formula of the capacitor is C = εA/d, where C is the capacitance (unit is farad F), ε is the permittivity of the dielectric between the two plates of the capacitor (unit is F/m), A is the area of the two plates of the capacitor (unit is m²), and d is the distance between the two plates (unit is m). In practical applications, the capacity of capacitors is often expressed by micromethod (μF) or picomethod (pF). Specifically, one micromethod is equal to one million picomethods (1 μF= 1,000,000 pF) and one picomethod is equal to 10,000 micromethods (1 pF = 0.00001 μF). When using a capacitor in a circuit, it is necessary to pay attention to its polarity. Polar capacitors can distinguish between positive and negative electrodes and must be used forward, otherwise the potential difference between capacitor plates will be very large, which may cause short circuit or damage to the capacitor. Capacitors without polarity can be connected in any direction. When selecting a capacitor, it is necessary to consider its parameters, such as rated voltage, capacity, tolerance, etc. In addition, it is also necessary to consider factors such as the life of the capacitor and the use environment to ensure the normal operation and extend the service life of the capacitor.