文档介绍：15 FREQUENCY DEPENDENCE
OF MATERIALS, THERMAL
RADIATION, AND NOISE
This the final chapter covers some miscellaneous but interesting topics
that relate to ics. An often overlooked aspect of electro-
ics is the fact that all materials possess varying ic
properties in different regions of the ic spectrum. I also
cover the basics of thermal radiation, which is the type of electromag-
netic radiation responsible for radiative heat transfer, and thermal circuit
noise. Both thermal radiation and thermal circuit noise are caused by
the random motion of charged particles, most notably electrons, inside
a material.
FREQUENCY DEPENDENCE OF MATERIALS
In electronics you spend your time with materials that have (approxi-
mately) constant properties in relation to frequency. However, no mate-
rial retains the same response over all frequencies. Many materials are
relatively constant at electronic frequencies, but almost all materials
undergo property changes in the infrared and/or visible bands. We are
quite fortunate that many materials go through changes in the visible
band, because the variations provide the many different colors that we
see and utilize to identify objects.
Conductors and Dielectrics
There are two basic types of materials, conductors and dielectrics. Con-
ductors are materials that support a current at DC. As such, they have
large concentrations of mobile charge. Most good conductors are metals,
but ionic solutions such as salt water are one example of nonmetal con-
ductors. The other major type of material is the dielectric or insulator.
Dielectrics are poor conductors at DC. There are of course materials that
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fall into the gray area in between the two types, but I will focus on the
distinctions to keep the topic clear.
Metals
Because metals are the monly used conductors, I will focus on
the properties of metallic conductors. At DC and radio frequencies, the
electron