ASTM A893-97
(Test Method)Standard Test Method for Complex Dielectric Constant of Nonmetallic Magnetic Materials at Microwave Frequencies
Standard Test Method for Complex Dielectric Constant of Nonmetallic Magnetic Materials at Microwave Frequencies
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 inch-pound units are to be regarded as the standard.
1.3 This standard does not purport to address all of the safety problems, 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.
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Standards Content (Sample)
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: A 893 – 97
Standard Test Method for
Complex Dielectric Constant of Nonmetallic Magnetic
Materials at Microwave Frequencies
This standard is issued under the fixed designation A 893; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope tially uniform electric and zero microwave magnetic fields.
The perturbation theory requires that the diameter of the
1.1 This test method covers the measurement of the com-
sample rod be small compared to one quarter of the wavelength
plex dielectric constant of isotropic ferrites for extremely
of the microwave radiation in the specimen. Estimation of this
high-frequency applications.
wavelength requires knowledge of the permittivity, e = ke , and
1.2 The values stated in either customary units or SI units
permeability, μ, of the specimen under the conditions of
are to be regarded separately as standard. Within the text, the
measurement. The wavelength, l, in the specimen is given by
SI units are shown in brackets. The values stated in each
the equation:
system are not exact equivalents; therefore, each system shall
1/2
be used independently of the other. Combining values from the
l5 1/f 8~μe! (2)
two systems may result in nonconformance with this specifi-
For many ferrites, μ may be taken equal to μ , the perme-
cation.
ability of empty space, without serious error. The permittivity,
1.3 This standard does not purport to address all of the
e, is determined by measurement as described below; after
safety concerns, if any, associated with its use. It is the
obtaining a value of e, it is necessary to ascertain with the aid
responsibility of the user of this standard to establish appro-
of Eq 1 that the sample diameter is sufficiently small.
priate safety and health practices and determine the applica-
2.4 This test method is not suitable for materials with loss
bility of regulatory limitations prior to use.
tangents $0.1, with the loss tangent defined as tan d = k 9/k 8.
2.5 The results of the perturbation theory calculation may be
2. Summary of Test Method
expressed in the form:
2.1 In an isotropic dielectric medium with a steady electric
o i o 2
df/f 5 2 k 2 1 |Miv E E dv /2|Miv E dv (3)
field, E, the electric displacement, D, is given by the equation: @ ~ ! # ~ !
s c
D 5 ke E (1)
where:
f = f 8+jf8/2Q;
where:
Q = loaded Q of the cavity;
e = permittivity of free space and
v = specimen volume contained within the cavity,
s
k = dielectric constant. If the medium is subjected to an
3 3
in. [mm ];
alternating electric field, the electric displacement is
3 3
v = cavity volume, in. [mm ]; and
c
not necessarily in phase with the field. This fact may
E = microwave electric field strength.
be expressed mathematically by taking k as a complex
The superscript o refers to fields in the empty cavity and the
quantity. If we write k = k 8 − jk 9, the imaginary part,
superscript i refers to fields inside the specimen.
k9, determines the dissipation in the medium.
2.6 A specific cavity suitable for this test method is a TE
10n
2.2 This test method uses a cavity perturbation technique as
rectangular cavity, where n is odd. With the rod running
a means of separating electric from magnetic effects. Quanti-
completely across the cavity at the center, Eq 2 for df/f can be
ties that must be measured are the resonance frequency, f,of
reduced to the following:
the cavity with and without the sample, the loaded Q of the
df 8/f 8522 k 8 2 1 v /v ; d 1/Q 5 4k 9 v /v (4)
~ !~ ! ~ ! ~ !
s c s c
cavity with and without the specimen, and the cavity and
specimen dimensions. df and d(1/Q) are, respectively, the difference in the cavity
2.3 The specimen is in the form of a rod and is placed
resonant frequency with and without the specimen and the
parallel to the microwave electric field in a region of substan-
difference in the reciprocal Q of the cavity with and without the
specimen, and f 8 is the resonant frequency of the empty cavity.
This test method is under the jurisdiction of ASTM Committee A-6 on
Magnetic Properties and is the direct responsibility of Subcommittee A06.01 on Test See, for example, Montgomery C. G., Ed., Technique of Microwave Measure-
Methods. ments, McGraw-Hill Book Co., Inc., New York, 1947, pp. 294–295; Bronwell and
Current edition approved Oct. 10, 1997. Published December 1998. Originally Beam, Theory and Application of Microwaves, McGraw-Hill Book Co., Inc., 1947,
published as C 525 – 63 T. Last previous edition F 131 – 86 (1991). pp. 368–337.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
A 893
2.7 In many cases it is convenient to describe the dissipative 5.4 The TE cavity (n odd and 3 or greater) shall be
10n
properties of the medium by alternative notation. An effective resonant between 9000 and 10 000 MHz for the X-band
resistivity at the frequency f 8 = u/2p may be defined by the measurement. The loaded Q of the empty cavity shall be
equation: greater than 2000 (Note 1). The holes through which the ferrite
passes shall be 0.042 + 0.002, − 0.000 in. [0.11 + 0.05, − 0.00
r5 1/vk 9e
o
mm] in diameter. The dimensions of a typical cavity, operating
(5)
in the TE mode, are shown in Fig. 2.
3. Significance and Use
NOTE 1—High Qs are obtainable by using waveguide and end plates of
3.1 This test method can be used to evaluate batch type or
oxygen-free high-conductivity copper or by silver plating.
co
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