An aluminum electrolytic capacitor with a non-solid electrolyte always
consists of two aluminum foils separated mechanically by a spacer,
mostly paper, which is saturated with a liquid or gel-like electrolyte.
One of the aluminum foils, the anode, is etched (roughened) to increase
the surface and oxidized (formed). The second aluminum foil, called the
“cathode foil”, serves to make electrical contact with the electrolyte. A
paper spacer mechanically separates the foils to avoid direct metallic
contact. Both foils and the spacer are wound and the winding is
impregnated with liquid electrolyte. The electrolyte, which serves as
cathode of the capacitor, covers the etched rough structure of the oxide
layer on the anode perfectly and makes the increased anode surface
effectual. After impregnation the impregnated winding is mounted in an
aluminum case and sealed.