A capacitor, also called a storage cell, secondary cell or condenser, is a passive electronic component that is capable of storing an electric charge. It is also a filter, blocking direct current (DC) and allowing alternating current (AC) to pass. A capacitor is composed of two conductive surfaces called electrodes, separated by an insulator, which is called a dielectric. Unlike some capacitors, a ceramic capacitor is not polarized, which means the two electrodes are not positive and negatively charged; and it uses layers of metal and ceramic as dielectrics.
When DC voltage is applied to a ceramic capacitor, the electric charge is stored in the electrodes. Storage capacity is small, and is measured in units called Farads (F). Most capacitors are so small, that their capacity is measured in microfarad (10 to the negative sixth power), nanofarad (ten to the negative ninth power), or picofarad (ten to the negative twelfth power) units. New super capacitors have been designed which actually hold enough charge to be measured in full Farad units.
The first ceramic capacitor design was in the 1930s, when it was used as a component in radio receivers and other vacuum tube equipment. Capacitors are now a vital component in numerous electronic applications, including automobile, computers, entertainment equipment, and power supplies. They also are helpful in maintaining voltage levels in power lines, improving electrical system efficiency and reducing energy loss.
The original ceramic capacitor design was disc-shaped, and with the exception of monolithic ceramic capacitors, that is still the predominate design. Ceramic capacitors use materials like titanium acid barium as the dielectric. They are not constructed in a coil, like some other capacitors, so they can be used in high frequency applications and in circuits which bypass high frequency signals to ground.
A monolithic ceramic capacitor is made up of thin dielectric layers interwoven with staggered metal-film electrodes. Once the leads are attached, the unit is pressed into a monolithic, or solid and uniform shape. The small size and high capacity of monolithic capacitors has helped to make possible the miniaturization, digitalization and high frequency in electronic equipment.
A multilayer ceramic capacitor uses two non-polarized electrodes separated by multiple alternating layers of metal and ceramic as the dielectric. These are found in high frequency power converters and in filters in switching power supplies and DC to DC converters. Computers, data processors, telecommunications, industrial controls and instrumentation equipment also use multilayer ceramic capacitors.
Ceramic capacitors are classified as Type I, Type II or Type III. The Type I ceramic capacitor generally has a dielectric made from a mixture of metal oxides and titanates. They have high insulation resistance and lower frequency losses and maintain a stable capacity even when voltage varies. These are used in resonant circuits, filters and timing elements.
Type II capacitors have dielectrics made from zirconates and titanates, such as barium, calcium and strontium. They have somewhat higher losses of frequency and less insulation resistance than Type I capacitors, but can still maintain high capacity levels. These are popular for use in coupling, blocking and filtering. One disadvantage of Type II capacitors is that they can lose capacity with age. Type III ceramic capacitors are general use capacitors that are adequate in applications which do not require high insulation resistance and capacity stability.