C hapter 4 Material Classes, structure, and properties
118
use the word insulator in referring to its inability to conduct electricity and to use dielectric in referring to its behavior in an electric
field.
Three properties are of importance here. The first, the dielectric
constant (or relative permittivity), has to do with the way the material acquires a dipole moment (it polarizes) in an electric field. The
second, the dielectric loss factor, measures the energy dissipated when
radio-frequency waves pass through a material, the energy appearing as heat (the principle of microwave cooking). The third is the
dielectric breakdown potential; lightning is dielectric breakdown,
and it can be as damaging on a small scale—in a piece of electrical
equipment, for example—as on a large one.
There are many kinds of electrical behavior, all of them useful.
Figure 4.48 gives an overview, with examples of materials and
applications.
resistivity and Conductivity
The electrical resistance R (units: ohms, symbol Ω) of a rod of material is the potential drop V (volts) across it, divided by the current
i (amps) passing through it, as in Figure 4.49. This relationship is
Ohm’s Law:
R
V
i
=
(4.25)
The material property that determines resistance is the electrical
resistivity, ρ e . It is related to the resistance by
Electrical materials
Conductors
Insulators
Non-piezoelectric
dielectrics
Piezoelectrics
Non-pyroelectric
Pyroelectric
Non-ferroelectric
Ferroelectric
Phenolics
(Electrical plugs
and switches)
Quartz
(Ultrasonic oscillator
ink-jet print-heads)
PZT
(Diesel injectors)
Barium titanate
(IR sensors
thermal imaging)
Copper
(Motors, dynamos)
Figure 4.48
The hierarchy of electrical behavior. The interesting
ones are in the darker colored boxes, with
examples of materials and applications. Their
nature and origins are described in this chapter.
118
use the word insulator in referring to its inability to conduct electricity and to use dielectric in referring to its behavior in an electric
field.
Three properties are of importance here. The first, the dielectric
constant (or relative permittivity), has to do with the way the material acquires a dipole moment (it polarizes) in an electric field. The
second, the dielectric loss factor, measures the energy dissipated when
radio-frequency waves pass through a material, the energy appearing as heat (the principle of microwave cooking). The third is the
dielectric breakdown potential; lightning is dielectric breakdown,
and it can be as damaging on a small scale—in a piece of electrical
equipment, for example—as on a large one.
There are many kinds of electrical behavior, all of them useful.
Figure 4.48 gives an overview, with examples of materials and
applications.
resistivity and Conductivity
The electrical resistance R (units: ohms, symbol Ω) of a rod of material is the potential drop V (volts) across it, divided by the current
i (amps) passing through it, as in Figure 4.49. This relationship is
Ohm’s Law:
R
V
i
=
(4.25)
The material property that determines resistance is the electrical
resistivity, ρ e . It is related to the resistance by
Electrical materials
Conductors
Insulators
Non-piezoelectric
dielectrics
Piezoelectrics
Non-pyroelectric
Pyroelectric
Non-ferroelectric
Ferroelectric
Phenolics
(Electrical plugs
and switches)
Quartz
(Ultrasonic oscillator
ink-jet print-heads)
PZT
(Diesel injectors)
Barium titanate
(IR sensors
thermal imaging)
Copper
(Motors, dynamos)
Figure 4.48
The hierarchy of electrical behavior. The interesting
ones are in the darker colored boxes, with
examples of materials and applications. Their
nature and origins are described in this chapter.