Capacitor types (wiki)
By dielectric material
* Vacuum : Two metal, usually copper, electrodes are separated by a vacuum. The insulating envelope is usually glass or ceramic. Typically of low capacitance - 10 - 1000 pF and high voltage, up to tens of kilovolts, they are most often used in radio transmitters and other high voltage power devices. Both fixed and variable types are available. Vacuum variable capacitors can have a minimum to maximum capacitance ratio of up to 100, allowing any tuned circuit to cover a full decade of frequency. Vacuum is the most perfect of dielectrics with a zero loss tangent. This allows very high powers to be transmitted without significant loss and consequent heating.
* Air : Air dielectric capacitors consist of metal plates separated by an air gap. The metal plates, of which there may be many interleaved, are most often made of aluminium or silver-plated brass. Nearly all air dielectric capacitors are variable and are used in radio tuning circuits.
* Plastic film: Made from high quality polymer film (usually polycarbonate, polystyrene, polypropylene, polyester (Mylar), and for high quality capacitors polysulfone), and metal foil or a layer of metal deposited on surface of the plastic film in a the metalized film type. They have good quality and stability, and are suitable for timer circuits. Their inductance limits use at high frequencies.
* Mica: Similar to glass. Often high voltage. Suitable for high frequencies. Expensive. Excellent tolerance & stability.
* Paper: Used for relatively high voltages. Known for long term failures.
* Glass: Used for high voltages. Expensive. Stable temperature coefficient in a wide range of temperatures.
* Ceramic: Chips of alternating layers of metal and ceramic, or disks of ceramic with metal on both sides of the disk. Characteristics vary widely depending on the type of ceramic dielectric. The dielectrics are broadly categorized as Class 1 or Class 2. Class 2 ceramic capacitors have strong variation of capacitance with temperature, high dissipation factor, high frequency coefficient of dissipation, and their capacitance depends on applied voltage and changes with aging. However they find massive use in common low-precision coupling and filtering applications. Suitable for high frequencies.
* Aluminum electrolytic: Polarized. One electrode made of aluminum foil, etched aluminium to acquire much larger surface area. The dielectric is oxide grown on the etched aluminum plate, and the second electrode is a liquid electrolyte. They can achieve high capacitance but suffer from poor tolerances, high instability, gradual loss of capacitance especially when subjected to heat, and high leakage current. The conductivity of the electrolyte drops at low temperatures, increasing equivalent series resistance. Bad frequency characteristics make them unsuited for high-frequency applications. Special types with low equivalent series resistance are available.
* Tantalum electrolytic: Similar to the aluminum electrolytic capacitor but with better frequency and temperature characteristics. High dielectric absorption and high leakage [4]. Although they share many of the disadvantages of aluminum electrolytics, they perform better on most attributes; for example, they have much better performance at low temperatures.
* OS-CON (or OC-CON) capacitors are a polymerized organic semiconductor solid-electrolyte type that offer longer life at higher cost than standard electrolytics.
* Supercapacitors: Made from carbon aerogel, carbon nanotubes, or highly porous electrode materials. Extremely high capacity. Can be used in some applications instead of rechargeable batteries.
* Varactors or varicap capacitors are specialized, reverse-biased diodes whose capacitance varies with voltage. Used in phase-locked loops, amongst other applications.
* AC capacitors are capacitors specifically designed to work on line (mains) voltage ac power circuits. These are commonly used electric motor circuits. They are often designed to handle large currents so they tend to be physically large. They are usually ruggedly packaged, often in metal cases that can be easily grounded/earthed. They also tend to have rather high DC breakdown voltages;
By construction
* Axial capacitors
* Feedthrough capacitors for RF decoupling usage
* Gimmick capacitors, made from two insulated wires that have been twisted together[citation needed]
* Radial capacitors
* Surface mount (leadless) capacitors
* Trimmer capacitors
o Beehive types
o Compression types
* Tuning capacitor (air spaced)
* Discoidal capacitors