11
Fundamentals of Electric Capacitors
vacuum is 1, represented as 1.00000, and other materials’ dielectric constants are relative to this value. For example, if a metal was used for the
dielectric instead of an insulator, the cell voltage would be zero according to Equation (1.20), and the corresponding dielectric constant would be
infinite. Table 1.1 lists several typical materials’ dielectric constant values
for reference.
1.3.1.1 Dielectric Polarization Mechanisms
A material can be used as a capacitor’s dielectric if it can be polarized when
an electric field is applied. To have polarization ability, a material should have
at least one of the following properties: (1) covalently bonded molecules that
possess some natural electron polarities through which they endure electrical stress and orbital deformation from an induced electrical field; (2) polarizable ions where displacement of the ion center occurs under electrical stress;
(3) dipole polarity causing dipole rotations; and (4) domain polarity where
entire domains undergo rotation induced by an electric field. This property is
strongly dependent upon frequency, voltage, and temperature, and can produce dielectric constants as large as 400,000 observed in ceramics. Figure 1.4
represents the polarization mechanism induced by an electric field [5].
1.3.1.2 Ceramic Dielectrics and Their Capacitors
A ceramic is a material composed of non-metal bonding inorganic compounds. Ceramic dielectric materials are insulating and include titanates,
porcelains, and metal oxides (see Table 1.1). A ceramic dielectric can be
designed according to the shape of a capacitor such as a disc or a rectangle.
Since 1930, ceramics have been widely used to construct capacitors for radio
receivers and in modern electronic equipment for decoupling and bypass
applications. For example, some non-polar ceramic capacitors consist of
alternating layers of metal and the several geometric designs of dielectric
ceramics can provide high capacitance within a small design.
Different applications of current ceramic capacitors have different requirements, such as accuracy, stability over a temperature and voltage range,
and volumetric efficiency. Ceramic-based capacitors are recognized to have
a typical accuracy to their nominal capacitance rating of 5% to 10% with a
deviation as low as 1%, offering high stability with a low dissipation factor.
However, they have the lowest volumetric efficiency and are primarily used
in applications requiring frequency filtering. Ceramic-based capacitors have
operating temperatures between 10°C and 200°C. Exceptions are the negative–positive–zero ceramic capacitors, as they do not vary with temperature
and offer a capacitance range between 1.0 picofarads to a few microfarads. In
addition, depending on the application, the accuracies can offset each other.
For example, a decrease in the accuracy of the capacitance can be offset by
the progressive improvements of volumetric efficiency.
Fundamentals of Electric Capacitors
vacuum is 1, represented as 1.00000, and other materials’ dielectric constants are relative to this value. For example, if a metal was used for the
dielectric instead of an insulator, the cell voltage would be zero according to Equation (1.20), and the corresponding dielectric constant would be
infinite. Table 1.1 lists several typical materials’ dielectric constant values
for reference.
1.3.1.1 Dielectric Polarization Mechanisms
A material can be used as a capacitor’s dielectric if it can be polarized when
an electric field is applied. To have polarization ability, a material should have
at least one of the following properties: (1) covalently bonded molecules that
possess some natural electron polarities through which they endure electrical stress and orbital deformation from an induced electrical field; (2) polarizable ions where displacement of the ion center occurs under electrical stress;
(3) dipole polarity causing dipole rotations; and (4) domain polarity where
entire domains undergo rotation induced by an electric field. This property is
strongly dependent upon frequency, voltage, and temperature, and can produce dielectric constants as large as 400,000 observed in ceramics. Figure 1.4
represents the polarization mechanism induced by an electric field [5].
1.3.1.2 Ceramic Dielectrics and Their Capacitors
A ceramic is a material composed of non-metal bonding inorganic compounds. Ceramic dielectric materials are insulating and include titanates,
porcelains, and metal oxides (see Table 1.1). A ceramic dielectric can be
designed according to the shape of a capacitor such as a disc or a rectangle.
Since 1930, ceramics have been widely used to construct capacitors for radio
receivers and in modern electronic equipment for decoupling and bypass
applications. For example, some non-polar ceramic capacitors consist of
alternating layers of metal and the several geometric designs of dielectric
ceramics can provide high capacitance within a small design.
Different applications of current ceramic capacitors have different requirements, such as accuracy, stability over a temperature and voltage range,
and volumetric efficiency. Ceramic-based capacitors are recognized to have
a typical accuracy to their nominal capacitance rating of 5% to 10% with a
deviation as low as 1%, offering high stability with a low dissipation factor.
However, they have the lowest volumetric efficiency and are primarily used
in applications requiring frequency filtering. Ceramic-based capacitors have
operating temperatures between 10°C and 200°C. Exceptions are the negative–positive–zero ceramic capacitors, as they do not vary with temperature
and offer a capacitance range between 1.0 picofarads to a few microfarads. In
addition, depending on the application, the accuracies can offset each other.
For example, a decrease in the accuracy of the capacitance can be offset by
the progressive improvements of volumetric efficiency.