page_title: Electrolytic capacitor
section_title: History
hierarchical_section_title: Electrolytic capacitor / History
caption_attribution_description: English: An early electrolytic capacitor from 1914. It consists of two sheets of foil about 3 cm square separated by a fabric sheet, immersed in an electrolyte solution, sealed inside a glass tube, with electrodes attached to the foils at either end. It had a capacitance on the order of 2 microfarads. It was used as a decoupling condenser in a crystal radio.
context_page_description: An electrolytic capacitor is a polarized capacitor whose anode or positive plate is made of a metal that forms an insulating oxide layer through anodization. This oxide layer acts as the dielectric of the capacitor. A solid, liquid, or gel electrolyte covers the surface of this oxide layer, serving as the cathode or negative plate of the capacitor. Due to their very thin dielectric oxide layer and enlarged anode surface, electrolytic capacitors have a much higher capacitance-voltage product per unit volume than ceramic capacitors or film capacitors, and so can have large capacitance values. There are three families of electrolytic capacitor: aluminum electrolytic capacitors, tantalum electrolytic capacitors, and niobium electrolytic capacitors.
  The large capacitance of electrolytic capacitors makes them particularly suitable for passing or bypassing low-frequency signals, and for storing large amounts of energy. They are widely used for decoupling or noise filtering in power supplies and DC link circuits for variable-frequency drives, for coupling signals between amplifier stages, and storing energy as in a flashlamp.
caption: Early small electrolytic capacitor from 1914. It had a capacitance of around 2 microfarads.
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