http://en.wikipedia.org/wiki/Electrolytic_capacitor
Aluminum electrolytic capacitor: compact but lossy, these are available in the range of <1 µF to 1 F with working voltages up to several hundred volts DC. The dielectric is a thin layer of aluminum oxide. They contain corrosive liquid and can burst if the device is connected backwards. The oxide insulating layer will tend to deteriorate in the absence of a sufficient rejuvenating voltage, and eventually the capacitor will lose its ability to withstand voltage if voltage is not applied. A capacitor to which this has happened can often be "reformed" by connecting it to a voltage source through a resistor and allowing the resulting current to slowly restore the oxide layer.[8] Bipolar electrolytics (also called Non-Polarised or NP capacitors) contain two capacitors connected in series opposition and are used when one electrode can be either positive or negative relative to the other at different instants. Bad frequency and temperature characteristics make them unsuited for high-frequency applications. Typical ESL values are a few nanohenries.[9]
Tantalum: compact, low-voltage devices up to several hundred µF, these have a lower energy density and are produced to tighter tolerances than aluminum electrolytics. Tantalum capacitors are also polarized because of their dissimilar electrodes. The cathode electrode is formed of sintered tantalum grains, with the dielectric electrochemically formed as a thin layer of oxide. The thin layer of oxide and high surface area of the porous sintered material gives this type a very high capacitance per unit volume. The cathode electrode is formed either of a liquid electrolyte connecting the outer can or of a chemically deposited semi-conductive layer of manganese dioxide, which is then connected to an external wire lead. A development of this type replaces the manganese dioxide with a conductive plastic polymer (polypyrrole) that reduces internal resistance and eliminates a self-ignition failure.[
Aluminum, and to a lesser extent tantalum, electrolytics have worse noise, leakage, drift with temperature and ageing, dielectric absorption, and inductance than other types of capacitor. Additionally, low temperature is a problem for most aluminum capacitors: for most types, capacitance falls off rapidly below room temperature while dissipation factor can be ten times higher at −25 °C than at 25 °C. Most limitations can be traced to the electrolyte. At high temperature, the water can be lost to evaporation, and the capacitor (especially the small sizes) may leak outright. At low temperatures, the conductance of the salts declines, raising the ESR, and the increase in the electrolyte's surface tension can cause reduced contact with the dielectric. The conductance of electrolytes generally has a very high temperature coefficient, +2%/°C is typical, depending on size. The electrolyte, particularly if degraded, is implicated in various reliability issues as well.
Polymer capacitors do not contain electrolyte. Wet Electrolytic capacitors contain a paper between the anode and cathode foil that is soaked with liquid electrolyte. Polymer capacitors use a paper which is impregnated with organic semiconductor crystal. It looks like carbon paper really although it is not.
Polymer capacitors are characterised by lower ESR and ability to handle higher ripple current than their wet electrolytic counterparts. They are also characterised by not changing their ESR when their operating temperature changes and also having a much longer life. Sanyo quotes a 10 times increase in lifetime for a 20degC reduction in operating temperature for their OS-CON polymer capacitors whist a wet electrolytic capacitor in comparison would increase lifetime by 4 times.
Chokes used in radio circuits are divided into two classes those designed to be used with audio frequencies, and the others to be used with radio frequencies. Audio frequency coils, usually called A.F. chokes, can have ferromagnetic iron cores to increase their inductance. Chokes for higher frequencies often have iron powder or ferrite cores (see Ferrite bead). Chokes for even higher frequencies have non-magnetic cores and low inductance simulating the effects of an air-core.
[edit]Solid-state chokes
Solid-state chokes (SSC) can manage higher currents than traditional chokes. They can help reduce the high frequency buzzing noises that occur when running under high electrical currents.