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Keysight Technologies
Materials Measurement:
Magnetic Materials
Application Brief
02 | Keysight | Materials Measurement: Dielectric Materials - Application Brief
Overview Permeability also varies with temperature. The desired measure-
ment system is one that can evaluate temperature characteristics
Ferrite materials are widely used in electronic equipment such as with sufficient accuracy over a wide frequency range using a
computers, communication devices, power management systems, simple operation.
etc. They serve as inductive components, transformers, magnets,
magnetic field absorbers and suppressors.
Solution
Continual exploration of new materials helps not only to improve
performance, but to reduce size and power consumption. Recent The complex permeability is derived by measuring the impedance
progress in the material science and nanotechnology area has of the magnetic material. It is done by winding some wire around
created new types of ferrite materials and components. the material and measuring the impedance with respect to the
ends of the wire. The result may change depending on how the
Evaluation of magnetic characteristics of those materials is wire is wound and how the magnetic field interacts with its sur-
important in predicting performance of the components. Perfor- roundings.
mance includes permeability and loss of the material at various
frequencies where the devices are used.
Impedance analyzers used with magnetic material fixtures pro-
vides precise, repeatable, cost-effective and an easy-to-operate
measurement system over a wide frequency range.
Figure 1. Method of measuring effective permeability
The Keysight 16454A magnetic material test fixture provides an
ideal structure, configuring a single-turn inductor with the mate-
rial molded into a toroidal shape. There is no leakage flux in the
single-turn inductor and the magnetic field in the fixture is strictly
calculated from the electromagnetic theory.
Problem
Complex permeability is a magnetic property of a material. Its
real and imaginary part represents the ability of a material to
conduct magnetic flux and the losses dissipated in the material
respectively. Material with large permeability is desired to reduce
size and weight. Losses should be minimized for maximum ef-
ficiency while large loss is required for magnetic shield.
Complex permeability is determined by the impedance of the
inductor formed with the material. In most cases, it is not a
constant over the frequency and must be characterized at the
frequency where the device is used. At higher frequencies, ac-
curate measurements are difficult due to the parasitic impedance
of the fixture. For low loss material, phase angle of the impedance
is critical however the phase accuracy is not sufficient in many
cases.
Figure 2. Structure of the 16454A
03 | Keysight | Materials Measurement: Dielectric Materials - Application Brief
The simple shape of the coaxial fixture and the toroidal mate- The graph below shows a permeability example of three different
rial under test allows not only the precise evaluation but the ferrite cores measured by the E4990A and the E4991B with the
wide frequency coverage. The 16454A magnetic material fixture 16454A fixture.
covers 1 kHz to 1 GHz when combined with the Keysight E4991B
impedance/material analyzer or the Keysight E4990A impedance
analyzer.
Errors due to the measurement system should be removed prior
to the measurement. The error due to the impedance analyzer
can be calibrated by three term error correction. At higher
frequencies, phase angle accuracy is enhanced by the low-loss
capacitor calibration built into the E4991B.
Another source of error is due to the fixture. Residual inductance
included in the fixture can be removed by a short calibration,
which compensates the residual inductance by measuring the
fixture without toroidal core.
2(Zm - Z s )