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Keysight Technologies
Basics of Measuring the
Dielectric Properties of Materials
Application Note
Contents
Introduction .......................................................................................3
Dialetic Theory .................................................................................4
Dielectric constant .....................................................................4
Permeability ..................................................................................7
Electromagnetic Propagation ......................................................8
Dialectric mechanisms .................................................................10
Orientation (dipolar) polarization .........................................11
Electronic and atomic polarization .....................................11
Relaxation time ..........................................................................12
Debye relation ............................................................................12
Cole-Cole diagram ...................................................................13
Ionic conductivity ......................................................................13
Interfacial or space charge polarization ...........................14
Measurement systems .................................................................15
Network analyzers ....................................................................15
Impedance analyzers and LCR meters ..............................16
Fixtures .........................................................................................16
Software ......................................................................................16
Measurement Techniques ...........................................................17
Coaxial probe .............................................................................17
Transmission line .......................................................................20
Free-space ..................................................................................23
Resonant cavity .........................................................................26
Parallel plate ..............................................................................29
Inductance measurement method ......................................30
Comparison of methods ..............................................................31
Keysight solutions .........................................................................32
References .......................................................................................33
Web resources ................................................................................34
2
Introduction
A wide variety of industries need a better understanding of the materials they are working with to
shorten design cycles, improve incoming inspection, process monitoring, and quality assurance. Every
material has a unique set of electrical characteristics that are dependent on its dielectric proper-
ties. Accurate measurements of these properties can provide scientists and engineers with valuable
information to properly incorporate the material into its intended application for more solid designs or
to monitor a manufacturing process for improved quality control.
A dielectric materials measurement can provide critical design parameter information for many elec-
tronics applications. For example, the loss of a cable insulator, the impedance of a substrate, or the
frequency of a dielectric resonator can be related to its dielectric properties. The information is also
useful for improving ferrite, absorber and packaging designs. More recent applications in the area of
aerospace, automotive, food and medical industries have also been found to benefit from knowledge
of dielectric properties.
Keysight Technologies, Inc. offers a variety of instruments, fixtures, and software to measure the
dielectric properties of materials. Keysight measurement instruments, such as network analyzers,
impedance analyzers and LCR meters range in frequency up to 1.1THz. Fixtures to hold the mate-
rial under test (MUT) are available that are based on coaxial probe, parallel plate, coaxial/waveguide
transmission lines, free-space and resonant cavity methods. The table below shows product examples
that can be measured by Keysight's material test solutions.
Table 1. Materials measurement applications example
Industry Applications/Products
Electronics Capacitor, substrates, PCB, PCB antenna, ferrites, magnetic recording heads,
absorbers, SAR phantom materials, sensor
Aerospace/Defense Stealth, RAM (Radiation Absorbing Materials), radomes
Industrial materials Ceramics and composites: IC package, aerospace and automotive components,
cement, coatings, bio-implants
Polymers and plastics: fibers, substrates, films, insulation materials
Hydrogel: disposable diaper, soft contact lens
Liquid crystal: displays
Rubber, semiconductors and superconductors
Other products containing these materials: tires, paint, adhesives, etc.
Food & Agriculture Food preservation (spoilage) research, food development for microwave, packaging,
moisture measurements
Forestry & Mining Moisture measurements in wood or paper, oil content analysis
Pharmaceutical & Medical Drug research and manufacturing, bio-implants, human tissue characterization,
biomass, chemical concentration, fermentation
Dielectric Theory
The dielectric properties that will be discussed here are permittivity and
permeability. Resistivity is another material property which will not be
discussed here. Information about resistivity and its measurement can be found
in the Keysight Application Note 1369-11. It is important to note that permittivity
and permeability are not constant. They can change with frequency,
temperature, orientation, mixture, pressure, and molecular structure of the
material.
Dielectric constant
A material is classified as "dielectric" if it has the ability to store energy when
an external electric field is applied. If a DC voltage source is placed across a
parallel plate capacitor, more charge is stored when a dielectric material is
between the plates than if no material (a vacuum) is between the plates. The
dielectric material increases the storage capacity of the capacitor by
neutralizing charges at the electrodes, which ordinarily would contribute to the
external field. The capacitance with the dielectric material is related to
dielectric constant. If a DC voltage source v is placed across a parallel plate
capacitor (Figure 1), more charge is stored when a dielectric material is
between the plates than if no material (a vacuum) is between the plates.
A +
C0 =
t A
C = C0k' V - - - -
C t + -
+
+ -
+
-
+
+ -
+
+
k' = er' =
C0