ASTM A893/A893M-03(2008)

Standard Test Method for Complex Dielectric Constant of Nonmetallic Magnetic Materials at Microwave Frequencies

SIGNIFICANCE AND USE
This test method can be used to evaluate batch type or continuous production of material for use in microwave applications. It may be used to determine the loss factors of microwave ferrites or help evaluate absorption materials for use in microwave ovens and other shielding applications.
The values obtained by use of this practice can be used as quality assurance information for process control, or both, when correlated to the chemistry or process for manufacturing the material.
SCOPE
1.1 This test method covers the measurement of the complex dielectric constant of isotropic ferrites for extremely high-frequency applications.
1.2 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard. Within this standard, SI units are shown in brackets.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

General Information

• Status: Historical
• Publication Date: 30-Apr-2008
• ICS: 29.030 - Magnetic materials
• Technical Committee: A06 - Magnetic Properties
• Drafting Committee: A06.01 - Test Methods

Relations

• Replaces: ASTM A893/A893M-03 - Standard Test Method for Complex Dielectric Constant of Nonmetallic Magnetic Materials at Microwave Frequencies
• Effective Date: 01-May-2008
• Referred By: ASTM D2520-21 - Standard Test Methods for Complex Permittivity (Dielectric Constant) of Solid Electrical Insulating Materials at Microwave Frequencies and Temperatures to 1650 °C
• Effective Date: 01-May-2008

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: A893/A893M − 03(Reapproved 2008)
Standard Test Method for
Complex Dielectric Constant of Nonmetallic Magnetic
Materials at Microwave Frequencies
This standard is issued under the fixed designationA893/A893M; the number immediately following the designation indicates the year
of original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.
A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope cavity with and without the specimen, and the cavity and
specimen dimensions.
1.1 This test method covers the measurement of the com-
plex dielectric constant of isotropic ferrites for extremely 2.3 The specimen is in the form of a rod and is placed
high-frequency applications. parallel to the microwave electric field in a region of substan-
tially uniform electric and zero microwave magnetic fields.
1.2 The values stated in either SI units or inch-pound units
The perturbation theory requires that the diameter of the
are to be regarded separately as standard. The values stated in
samplerodbesmallcomparedtoonequarterofthewavelength
each system may not be exact equivalents; therefore, each
of the microwave radiation in the specimen. Estimation of this
system shall be used independently of the other. Combining
wavelengthrequiresknowledgeofthepermittivity, ε= kε ,and
values from the two systems may result in non-conformance
permeability, µ, of the specimen under the conditions of
with the standard. Within this standard, SI units are shown in
measurement. The wavelength, λ, in the specimen is given by
brackets.
the equation:
1.3 This standard does not purport to address all of the
1/2
λ 51/f' µε (2)
~ !
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
For many ferrites, µ may be taken equal to µ , the perme-
priate safety and health practices and determine the applica-
ability of empty space, without serious error. The permittivity,
bility of regulatory limitations prior to use.
ε, is determined by measurement as described below; after
obtaining a value of ε, it is necessary to ascertain with the aid
2. Summary of Test Method
of Eq 1 that the sample diameter is sufficiently small.
2.1 In an isotropic dielectric medium with a steady electric
2.4 This test method is not suitable for materials with loss
field, E, the electric displacement, D, is given by the equation:
tangents ≥0.1, with the loss tangent defined as tan δ= k "⁄k'.
D 5 kε E (1)
0 2.5 Theresultsoftheperturbationtheorycalculationmaybe
expressed in the form:
where:
o i o 2
δf/f 5 2 k 2 1 ?Miv E E dv /2?Miv E dv (3)
@ ~ ! # ~ !
ε = permittivity of free space and
s c
k = dielectric constant. If the medium is subjected to an
where:
alternatingelectricfield,theelectricdisplacementisnot
f = f'+jf'/2Q;
necessarily in phase with the field. This fact may be
Q = loaded Q of the cavity;
expressed mathematically by taking k as a complex
v = specimen volume contained within the cavity,
s
quantity. If we write k= k'− jk ", the imaginary part,
3 3
in. [mm ];
k", determines the dissipation in the medium. 3 3
v = cavity volume, in. [mm ]; and
c
E = microwave electric field strength.
2.2 This test method uses a cavity perturbation technique as
a means of separating electric from magnetic effects. Quanti-
The superscript o refers to fields in the empty cavity and the
ties that must be measured are the resonance frequency, f,of
superscript i refers to fields inside the specimen.
the cavity with and without the sample, the loaded Q of the
2.6 Aspecific cavity suitable for this test method is a TE
10n
rectangular cavity, where n is odd. With the rod running
This test method is under the jurisdiction of ASTM Committee A06 on
MagneticPropertiesandisthedirectresponsibilityofSubcommitteeA06.01onTest
Methods. See, for example, Montgomery, C. G., Ed., Technique of Microwave
Current edition approved May 1, 2008. Published June 2008. Originally Measurements, McGraw-Hill Book Co., Inc., New York, 1947, pp. 294–295;
approved in 1963. Last previous edition approved in 2003 as A893/A893M–03. Bronwell and Beam , Theory and Application of Microwaves, McGraw-Hill Book
DOI: 10.1520/A0893_A0893M-03R08. Co., Inc., 1947, pp. 368–337.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
A893/A893M − 03 (2008)
completely across the cavity at the center, Eq 2 for δf/f can be a line of constant microwave electric field and zero microwave
reduced to the following: magnetic field. The ends of the rod shall pass through holes in
both cavity walls.
δf'/f'522 k'21 v /v ; δ 1/Q 5 4k" v /v (4)
~ !~ ! ~ ! ~ !
s c s c
5.2 The rod diameter shall be 0.041+0.000,−0.002 in.
δf and δ(1/Q) are, respectively, the difference in the cavity
[0.10+0.00,−0.05 mm] at X-band unless this violates the
resonant frequency with and without the specimen and the
conditions of 2.3.
differenceinthereciprocal Qofthecavitywithandwithoutthe
5.3 The input and output lines of this cavity shall be made
specimen, and f' is the resonant frequency of the empty cavity.
to appear as matched loads by the appropriate use of pads or
2.7 Inmanycasesitisconvenienttodescribethedissipative
isolators.
properties of the medium by alternative notation. An effective
5.4 The TE cavity (n odd and 3 or greater) shall be
10 n
resistivity at the frequency f'= θ⁄2π may be defined by the
resonant between 9000 and 10 000 MHz for the X-band
equation:
measurement. The loaded Q of the empty cavity shall be
ρ 51/ωk"ε (5)
o
greaterthan2000(Note1).Theholesthroughwhichtheferrite
passes shall
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