page_title: Aluminum electrolytic capacitor
section_title: Impedance
hierarchical_section_title: Aluminum electrolytic capacitor / Electrical parameters / Impedance
caption_attribution_description: Impedanzkurven verschiedener Kapazitätswerte aus unterschiedlichen Kondensatorfamilien
context_page_description: Aluminium electrolytic capacitors are polarized electrolytic capacitors whose anode electrode is made of a pure aluminum foil with an etched surface. The aluminum forms a very thin insulating layer of aluminium oxide by anodization that acts as the dielectric of the capacitor. A non-solid electrolyte covers the rough surface of the oxide layer, serving in principle as the second electrode of the capacitor. A second aluminum foil called “cathode foil” contacts the electrolyte and serves as the electrical connection to the negative terminal of the capacitor.
  Aluminum electrolytic capacitors are divided into three subfamilies by the type of electrolyte:
  non-solid aluminum electrolytic capacitors,
  solid manganese dioxide aluminum electrolytic capacitors, and
  solid polymer aluminium electrolytic capacitors.
  Aluminum electrolytic capacitors with non-solid electrolyte are the most inexpensive type and also those with widest range of sizes, capacitance and voltage values. They are made with capacitance values from 0.1 µF up to 2,700,000 µF, and rated voltages values from 4 V up to 630 V. The liquid electrolyte provides oxygen for re-forming or self-healing of the dielectric oxide layer.
context_section_description: In general, a capacitor is seen as a storage component for electric energy. But this is only one capacitor function. A capacitor can also act as an AC resistor. Especially aluminum electrolytic capacitors are used in many applications as a decoupling capacitors to filter or bypass undesired biased AC frequencies to the ground or for capacitive coupling of audio AC signals. Then the dielectric is used only for blocking DC. For such applications the AC resistance, the impedance is as important as the capacitance value.
  The impedance is the vector sum of reactance and resistance; it describes the phase difference and the ratio of amplitudes between sinusoidally varying voltage and sinusoidally varying current at a given frequency in an AC circuit. In this sense impedance can be used like Ohm's law
  In other words, impedance is a frequency-dependent AC resistance and possesses both magnitude and phase at a particular frequency. 
  In capacitor data sheets, only the impedance magnitude |Z| is specified, and simply written as "Z". In this sense the impedance is a measure of the capacitor's ability to pass alternating currents.
  Impedance can be calculated using the idealized components of a capacitor's series-equivalent circuit, including an ideal capacitor ,  a resistor ,  and an inductance .  In this case the impedance at the angular frequency   is therefore given by the geometric (complex) addition of ESR, by a capacitive reactance (Capacitance)
  and by an inductive reactance (Inductance)
  .
  Then  is given by
  .
  In the special case of resonance, in which the both reactive resistances  and  have the same value (), then the impedance is only determined by .
  The impedance specified in the data sheets of various capacitors often shows typical curves for different capacitance values. The impedance at the resonant frequency defines the best working point for coupling or decoupling circuits. The higher the capacitance the lower the operable frequency range. Due to their large capacitance values, aluminum electrolytic capacitors have relatively good decoupling properties in the lower frequency range up to about 1 MHz or a little more. This and the relatively low price is often the reason for using electrolytic capacitors in 50/60 Hz standard or switched-mode power supplies.
caption: Typical impedance curves for different capacitance values as a function of frequency showing the typical form with decreasing impedance values below resonance and increasing values above resonance. The higher the capacitance, the lower the resonance frequency.
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