•Air-gap: These capacitors have low dielectric
losses and are ideal for tunable capacitors for resonating
•Glass: These capacitors are extremely stable
•Paper: Often found in antique radio equipment,
they have up to 25,000V for large oil-impregnated energy
•Polycarbonate: These make good filters, have a low
temperature coefficient, age well, but are expensive.
•Polyester: These range from about 1 nF to 1 µF and
are ideal signal capacitors and integrators.
•Polystyrene: These usually come in small values
(picoFarad range) and are stable signal capacitors.
•Polypropylene: These low-loss, high voltage signal
capacitors are resistant to breakdown.
•Teflon™ : These have
higher performance and are
more expensive than other
•Silvered Mica: These
are fast and stable for
HF and low VHF RF
circuits, but expensive
(see Figure 7).
capacitors have a larger
capacitance per unit
volume than other
types but, as previously
mentioned, are limited to
low frequency electrical
circuits, e.g., in power supply
filters or as coupling capacitors in audio amplifiers.
Figure 7. A silver
mica capacitor used in a
resonating HF antenna
Figure 8a. An electrolytic capacitor’s architecture.
Now to contradict myself, an ultra-capacitor is indeed
like a rechargeable battery. It stores a huge charge proportional to its capacitance. It differs from an electrolytic
since it uses electrical double-layer architecture. Figure 8a
shows the standard electrolytic architecture with a dielectric substrate sandwiched between two electrodes. Figure
8b shows that it is wound around like a jelly roll. Figure 8c
shows the materials used in an electrolytic capacitor. A
surface mount (SMD) capacitor also has layered dielectrics
and electrodes; however, it does not use the superior
material and technologies (discussed next) inherent in
super-capacitors (see Figure 9). Electric double-layer
ultra-capacitors add a second dielectric layer that works
in parallel with the first layer
(see Figure 10). This extra layer
An SMC capacitor
that used fused
layers of both its
dielectric and its
that uses special
layers of materials
very effectively to
unit area than its
A different view of an
August 2009 61
manufacturers use in