Basic concepts and structural principles of film capacitors and electrolytic capacitors
Film capacitors are capacitors made by using polymer films (such as polyester, polypropylene, etc.) as dielectrics and forming electrodes on the film surface through vacuum evaporation or metallization processes. Its basic structure consists of alternating layers of dielectric films and metal electrodes, and can be divided into many types according to different film materials and processes. The working principle of film capacitors is based on dielectric polarization. When voltage is applied, the dipoles in the dielectric are oriented to form an electric field, thereby storing electrical energy.
Electrolytic capacitors use metal oxides as dielectrics, anodized films of valve metals (aluminum, tantalum, etc.) as insulating layers, and cathodes are provided by electrolytes or conductive polymers. Its core structure includes anode foil, dielectric oxide layer, electrolyte, and cathode foil. The working principle of electrolytic capacitors depends on electrochemical processes, and the extremely thin oxide film (nanometer thickness) formed by anodization enables it to achieve extremely high unit area capacity.
From the perspective of the dielectric material system, the polymer materials used in film capacitors have stable chemical properties and uniform dielectric properties, while the oxide film dielectric of electrolytic capacitors exhibits nonlinear dielectric properties. This fundamental material difference determines the significant difference between the two in performance and application areas.