IEC 61788-7:2002
(Main)Superconductivity - Part 7: Electronic characteristic measurements - Surface resistance of superconductors at microwave frequencies
Superconductivity - Part 7: Electronic characteristic measurements - Surface resistance of superconductors at microwave frequencies
Describes measurement of the surface resistance of superconductors at microwave frequencies by the standard two-resonator method. The object of measurement is the temperature dependence of Rs at the resonant frequency.
General Information
Relations
Standards Content (Sample)
INTERNATIONAL IEC
STANDARD
61788-7
First edition
2002-01
Superconductivity –
Part 7:
Electronic characteristic measurements –
Surface resistance of superconductors
at microwave frequencies
Supraconductivité –
Partie 7:
Mesures des caractéristiques électroniques –
Résistance de surface des supraconducteurs
aux hyperfréquences
Reference number
Publication numbering
As from 1 January 1997 all IEC publications are issued with a designation in the
60000 series. For example, IEC 34-1 is now referred to as IEC 60034-1.
Consolidated editions
The IEC is now publishing consolidated versions of its publications. For example,
edition numbers 1.0, 1.1 and 1.2 refer, respectively, to the base publication, the
base publication incorporating amendment 1 and the base publication incorporating
amendments 1 and 2.
Further information on IEC publications
The technical content of IEC publications is kept under constant review by the IEC,
thus ensuring that the content reflects current technology. Information relating to
this publication, including its validity, is available in the IEC Catalogue of
publications (see below) in addition to new editions, amendments and corrigenda.
Information on the subjects under consideration and work in progress undertaken
by the technical committee which has prepared this publication, as well as the list
of publications issued, is also available from the following:
• IEC Web Site (www.iec.ch)
• Catalogue of IEC publications
The on-line catalogue on the IEC web site (www.iec.ch/catlg-e.htm) enables
you to search by a variety of criteria including text searches, technical
committees and date of publication. On-line information is also available on
recently issued publications, withdrawn and replaced publications, as well as
corrigenda.
• IEC Just Published
This summary of recently issued publications (www.iec.ch/JP.htm) is also
available by email. Please contact the Customer Service Centre (see below) for
further information.
• Customer Service Centre
If you have any questions regarding this publication or need further assistance,
please contact the Customer Service Centre:
Email: custserv@iec.ch
Tel: +41 22 919 02 11
Fax: +41 22 919 03 00
INTERNATIONAL IEC
STANDARD
61788-7
First edition
2002-01
Superconductivity –
Part 7:
Electronic characteristic measurements –
Surface resistance of superconductors
at microwave frequencies
Supraconductivité –
Partie 7:
Mesures des caractéristiques électroniques –
Résistance de surface des supraconducteurs
aux hyperfréquences
IEC 2002 Copyright - all rights reserved
No part of this publication may be reproduced or utilized in any form or by any means, electronic or
mechanical, including photocopying and microfilm, without permission in writing from the publisher.
International Electrotechnical Commission 3, rue de Varembé Geneva, Switzerland
Telefax: +41 22 919 0300 e-mail: inmail@iec.ch IEC web site http://www.iec.ch
Commission Electrotechnique Internationale
PRICE CODE
T
International Electrotechnical Commission
For price, see current catalogue
– 2 – 61788-7 IEC:2002(E)
CONTENTS
FOREWORD.3
INTRODUCTION.4
1 Scope.5
2 Normative references .5
3 Terms and definitions .5
4 Requirements .6
5 Theory and calculation equations .6
6 Apparatus.9
7 Measurement procedure.11
8 Precision and accuracy of the test method.15
9 Test Report .17
Annex A (informative) Additional information relating to clauses 1 to 8.18
Bibliography.25
Figure 1 – Configuration of a cylindrical dielectric rod resonator short-circuited at both
ends by two parallel superconductor films deposited on dielectric substrates.6
Figure 2 – Computed results of the u-v and W-v relations for TE mode .8
01p
Figure 3 – Configuration of standard dielectric rods for measurement of tan δ .8
Figure 4 – Schematic diagram of measurement equipment for temperature dependence
of R using a cryocooler .9
s
Figure 5 – Measurement apparatus for R .10
s
Figure 6 – Frequency response of dielectric resonator using sapphire (ε’ = 9,4) . 13
Figure 7 – Insertion attenuation IA, resonant frequency f
and half power bandwidth Δf, measured at T Kelvin .13
Figure 8 – Reflection scattering parameters (S and S ) .15
11 22
Figure 9 – Term definitions in Table.16
Figure A.1 – Schematic configuration of several measurement methods for the surface
resistance .19
Figure A.2 – Three types of dielectric resonators .20
Figure A.3 – The mode chart to design TE resonator short-circuited at both ends by
parallel superconductor films[11] .22
Figure A.4 – The mode chart to design TE resonator short-circuited at both ends by
parallel superconductor films[11, 12].23
Figure A.5 – Relationship between d and f of the TE resonator for ε’ of the
0 011
sapphire rod .23
61788-7 © IEC:2002(E) – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SUPERCONDUCTIVITY –
Part 7: Electronic characteristic measurements –
Surface resistance of superconductors at microwave frequencies
FOREWORD
1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of the IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, the IEC publishes International Standards. Their preparation is
entrusted to technical committees; any IEC National Committee interested in the subject dealt with may
participate in this preparatory work. International, governmental and non-governmental organizations liaising
with the IEC also participate in this preparation. The IEC collaborates closely with the International
Organization for Standardization (ISO) in accordance with conditions determined by agreement between the
two organizations.
2) The formal decisions or agreements of the IEC on technical matters express, as nearly as possible, an
international consensus of opinion on the relevant subjects since each technical committee has representation
from all interested National Committees.
3) The documents produced have the form of recommendations for international use and are published in the form
of standards, technical specifications, technical reports or guides and they are accepted by the National
Committees in that sense.
4) In order to promote international unification, IEC National Committees undertake to apply IEC International
Standards transparently to the maximum extent possible in their national and regional standards. Any
divergence between the IEC Standard and the corresponding national or regional standard shall be clearly
indicated in the latter.
5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with one of its standards.
6) Attention is drawn to the possibility that some of the elements of this International Standard may be the subject
of patent rights. The IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61788-7 has been prepared by IEC technical committee 90:
Superconductivity.
The text of this standard is based on the following documents:
FDIS Report on voting
90/111/FDIS 90/117/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives.
Annex A is for information only.
The committee has decided that the contents of this publication will remain unchanged until
2006. At this date, the publication will be
• reconfirmed;
• withdrawn;
• replaced by a revised edition, or
• amended.
A bilingual version of this standard may be issued at a later date.
– 4 – 61788-7 IEC:2002(E)
INTRODUCTION
Since the discovery of some Perovskite-type Cu-containing oxides, extensive R & D work on
high-temperature oxide superconductors has been, and is being, made worldwide, and its
application to high-field magnet machines, low-loss power transmission, electronics and many
other technologies is in progress.
In various fields of electronics, especially in telecommunication fields, microwave passive
devices such as filters using oxide superconductors are being developed and are undergoing
on-site testing [1,2] .
Superconductor materials for microwave resonators, filters, antenna and delay lines have the
advantage of very low loss characteristics. Knowledge of this parameter is of primary
importance for the development of new materials on the supplier side and for the design of
superconductor microwave components on the customer side. The parameters of
superconductor materials needed for the design of microwave components are the surface
resistance R and the temperature dependence of the surface resistance.
s
Recent advances in high Tc superconductor (HTS) thin films with R several orders of
s
magnitude lower than that of normal metals have increased the need for a reliable
characterization technique to measure this property [3,4]. Traditionally, the R of Nb or any
s
other low temperature superconducting material was measured by first fabricating an entire
three dimensional resonant cavity and then measuring its Q-value. The R could be calculated
s
by solving the EM field distribution inside the cavity. Another technique involves placing a
small sample inside a larger cavity. This technique has many forms but usually involves the
uncertainty introduced by extracting the loss contribution due to the HTS films from the
experimentally measured total loss of the cavity.
The best HTS samples are epitaxial films grown on flat crystalline substrates and no high
quality films have been grown on any curved surface so far. What is needed is a technique
that: can use these small flat samples; requires no sample preparation; does not damage or
th
change the film; is highly repeatable; has great sensitivity (down to 1/1000 the R of
s
copper); has great dynamic range (up to the R of copper); can reach high internal powers
s
with only modest input powers; and has broad temperature coverage (4,2 K to 150 K).
The dielectric resonator method is selected among several methods [5,6,7] to determine the
surface resistance at microwave frequencies because it is considered to be the most popular
and practical at present. Especially, the sapphire resonator is an excellent tool for measuring
the R of HTS materials [8].
s
The test method given in this standard can be also applied to other superconductor bulk
plates including low Tc material.
This standard is intended to provide an appropriate and agreeable technical base for the time
being to engineers working in the fields of electronics and superconductivity technology.
The test method covered in this standard is based on the VAMAS (Versailles Project on
Advanced Materials and Standards) pre-standardization work on the thin film properties of
superconductors.
———————
Numbers in brackets refer to the bibliography.
61788-7 © IEC:2002(E) – 5 –
SUPERCONDUCTIVITY –
Part 7: Electronic characteristic measurements –
Surface resistance of superconductors at microwave frequencies
1 Scope
This part of IEC 61788 describes measurement of the surface resistance of superconductors
at microwave frequencies by the standard two-resonator method. The object of measurement
is the temperature dependence of R at the resonant frequency.
s
The applicable measurement range of surface resistances for this method is as follows:
–Frequency: 8 GHz < f < 30 GHz
– Measurement resolution: 0,01 mΩ at 10 GHz
The surface resistance data at the measured frequency, and that scaled to 10 GHz, assuming
the f rule (f < 30 GHz) for comparison, shall be reported.
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC 60050-815, International Electrotechnical Vocabulary – Part 815: Superconductivity
3 Terms and definitions
For the purposes of this standard, the definitions given in IEC 60050-815 apply.
In general, surface impedance Z for conductors, including superconductors, is defined as the
s
ratio of the electric field E to the magnetic field H , tangential to a conductor surface:
t t
Z = E /H = R + jX
s t t s s
where R is the surface resistance and X is the surface reactance.
s s
– 6 – 61788-7 IEC:2002(E)
4 Requirements
The surface resistance R of a superconductor film shall be measured by applying a
s
microwave signal to a dielectric resonator with the superconductor film specimen and then
measuring the attenuation of the resonator at each frequency. The frequency shall be swept
around the resonant frequency as the centre, and the attenuation – frequency characteristics
shall be recorded to obtain Q-value, which corresponds to the loss.
The target precision of this method is a coefficient of variation (standard deviation divided by
the average of the surface resistance determinations) that is less than 20 % for the
measurement temperature range from 30 K to 80 K.
It is the responsibility of the user of this standard to consult and establish appropriate safety
and health practices and to determine the applicability of regulatory limitations prior to use.
Hazards exist in this type of measurement. The use of a cryogenic system is essential to cool
the superconductors to allow transition into the superconducting state. Direct contact of skin
with cold apparatus components can cause immediate freezing, as can direct contact with a
spilled cryogen. The use of an r.f.-generator is also essential to measure high-frequency
properties of materials. If its power is too high, direct contact to human bodies can cause an
immediate burn.
5 Theory and calculation equations
Figure 1 shows the configuration of the TE mode resonator, which is used to eliminate the
0mp
air-gap effects. A cylindrical dielectric rod with diameter, d, and height, h, is short-circuited at
both ends by surfaces of two parallel superconductor films deposited on dielectric substrates
with diameter, d′, thus constituting a resonator. These superconductor films are required to
have the same value of R . The value of R is calculated from the measured resonant
s s
frequency f and unloaded quality factor Q for the TE resonance mode. When the two
0 u 0mp
superconductor films have different values of R , the measured R value corresponds to the
s s
average value of these two films.
∅d’
∅d
z
Superconductor
h
films
y
Dielectric rod
x
IEC 001/02
Figure 1 – Configuration of a cylindrical dielectric rod resonator short-circuited
at both ends by two parallel superconductor films deposited on dielectric substrates
61788-7 © IEC:2002(E) – 7 –
The value of R is given by
s
1 A
R = − tan δ (1)
s
B Q
u
where
W
A = 1 + (2)
ε'
λ 1 + W
= = ⋅ ⋅ ⋅
B p , p 1,2, , (3)
2h
30π ε'
c
λ = (4)
f
J (u) K (v)K (v) − K (v)
1 0 2
W = (5)
2 2
K (v) J (u) − J (u)J (u)
1 1 0 2
pλ
2 0
πd
= -1 (6)
v
λ
0
2h
(u) (v)
J K
0 0
u = -v (7)
(u) (v)
J K
1 1
In equations (1) and (2), ε’ and tan δ are the relative permittivity and the loss factor of the
dielectric rod, respectively. In equations (3) and (4), λ is the free space resonant wavelength,
and c is the velocity of light in a vacuum (c = 2,9979 × 10 m/s). The function W/ε´ equals the
ratio of electric-field energy stored outside to that stored inside the dielectric rod. If all of the
electric field is concentrated inside the dielectric rod, the value W equals zero. The value u is
given by the transcendental equation (7) using the value of v , where J (u) is the Bessel
n
function of the first kind and K (v) is the modified Bessel function of the second kind,
n
respectively. For any value of v, the m-th solution u exists between u and u , where
0m 1m
J (u ) = 0 and J (u ) = 0. The first solution (m = 1), which is used for easy mode
0 0m 1 1m
identification, is shown in figure 2 by curve (A). The computed result of the W-v relation for
m = 1 of TE resonance mode is shown in figure 2 by curve (B).
0mp
– 8 – 61788-7 IEC:2002(E)
1,2
2 2
1,0
(A) u (v )
0,8
0,6
0,4
6 0,2
(B) w (v )
0 2 4 6 8 10 12 14 16
v
IEC 002/02
Figure 2 – Computed results of the u-v and W-v relations for TE mode
01p
The value of ε’ is given by
λ
2 2
ε' = ()+ + 1 (8)
u v
πd
2 2
using the value of v and u .
In the two-resonator method, a pair of dielectric rods, which are called "standard dielectric
rods", are used. These two rods have the same diameter but have different heights. The rod
heights are such that one rod is p times the height of the other; p is commonly set equal to
three. They are required to have the same values of ε’ and tan δ.
Figure 3 shows the configuration of the standard dielectric rods in the case of p = 3. To avoid
confusion, the height of the short standard dielectric rod is denoted by h . Each resonator is
called "TE resonator" and "TE resonator", respectively. The same superconductor films
011 013
are used in these resonators. The values of f and Q for the TE mode are measured using
0 u 011
the TE resonator, and those for the TE mode are measured using the TE resonator.
011 01p 01p
We denote the f and Q for each resonator by using the subscripts 1 and p, respectively: f
0 u 01
and Q for TE resonator, and f and Q for TE resonator.
u1 011 0p up 01p
Superconductor film
∅
d
∅d
Dielectric rod
3h
h
Line of electric force
Line of magnetic force
IEC 003/02
Figure 3 – Configuration of standard dielectric rods for measurement of tan δδδδ
u
w
61788-7 © IEC:2002(E) – 9 –
The value of tan δ is given from the measured values of Q . When the TE resonator is
u 01p
precisely p times longer than the TE resonator, f coincides with f . However Q is
011 0p 01 up
higher than Q according to the different magnitude of the electric field energy stored in the
u1
two resonators. Owing to the fact that both dielectric rods are short-circuited at both ends by
the same superconductor films, equation (1) yields
A p 1
tanδ = - (9)
( p -1) Q Q
up u1
As an alternative method, the value of R of superconductor films can be directly measured by
s
2h
30π p ε'+ W 1 1
=
R − (10)
s
()p − 1 1 + W Q Q
u1 up
λ0
where equation (10) is derived by substituting equation (9) into equation (1).
6 Apparatus
6.1 Measurement equipment
Figure 4 shows a schematic diagram of the equipment required for the microwave measure-
ment. The equipment consists of a network analyzer system for transmission measurement, a
measurement apparatus, and a thermometer for monitoring the measuring temperature.
An incident power generated from a suitable microwave source such as a synthesized
sweeper is applied to the dielectric resonator fixed in the measurement apparatus. The
transmission characteristics are shown on the display of the network analyzer.
Vector network
analyser
Synthesized
sweeper
Thermometer
S-parameter
test set
Thermal sensor
Measurement apparatus
Cryocooler
IEC 004/02
Figure 4 – Schematic diagram of measurement equipment for temperature dependence
of R using a cryocooler
s
System interface
– 10 – 61788-7 IEC:2002(E)
The measurement apparatus is fixed in a temperature-controlled cryocooler.
For the measurement of R for superconductor films, a vector network analyzer is recom-
s
mended. A vector network analyzer has better measurement accuracy than a scalar network
analyzer due to its wide dynamic range.
6.2 Measurement apparatus for R
s
Figure 5 shows a schematic of a typical open type measurement apparatus for the R of
s
superconductor films deposited on a substrate with a flat surface. The upper superconductor
film is pressed down by a spring, which is made of phosphor bronze. The plate type spring is
recommended to be used for the improvement of measurement accuracy. This type of spring
reduces the friction between the spring and the other part of the apparatus, and allows the
smooth movement of superconductor films due to the thermal expansion of the dielectric rod.
The height of spring support shall be changed according to the height of the standard
dielectric rod.
Each of the two semi-rigid cables shall have a small loop at the top. The plane of the loop
shall be set parallel to that of the superconductor films in order to suppress the unwanted
TM modes. The coupling loops shall be carefully checked prior to the measurements to
mn0
keep the good coupling conditions. These cables can move right and left to adjust the
insertion attenuation (IA). In this adjustment, coupling of unwanted cavity modes to the
interested dielectric resonance mode shall be suppressed. Unwanted, parasitic coupling to
the other modes reduces the high Q value of the TE mode resonator. For suppressing the
parasitic coupling, special attention shall be paid to designing high Q resonators. Two other
types of resonators, not including the open type shown in figure 5, are recommendable. They
are explained in A.3.
A
A
Spot welding
Loop
Plate type spring
Dielectric rod
Superconductor film
Semi-rigid cable Spring
support
Reference line
Connector
IEC 005/02
Figure 5 – Measurement apparatus for R
s
A reference line made of a semi-rigid cable, shown in figure 5, shall be used to measure the
full transmission power level, i.e., the reference level. This cable has a length equal to the
sum of the two cables of the measurement apparatus. The semi-rigid cable with the outer
diameter of 1,20 mm is recommended.
In order to minimize the measurement error, two superconductor films shall be set to be
parallel to each other.
61788-7 © IEC:2002(E) – 11 –
6.3 Dielectric rods
Two dielectric rods with the same ε’ and tan δ, preferably cut from one cylindrical dielectric
rod, are required. These two rods, standard dielectric rods, shall have the same diameter but
different heights: one has a height three times longer than the other.
It is preferable to use standard dielectric rods with low tan δ to achieve the requisite
measurement accuracy on R . Recommended dielectric rods are sapphire rods cut in the
s
direction parallel to c-axis (ε´ = 9,4).
The diameter and the heights of the standard sapphire rods shall be carefully designed so
that the TE and TE mode do not couple to other TM or HM modes, since the coupling
011 013
between TE mode and other modes causes the degradation of unloaded Q. Design guideline
for the standard sapphire rods is described in A.4. Table 1 shows typical examples of
dimensions of the standard sapphire rods for 12 GHz resonance.
Table 1 – Typical dimensions of a pair of standard sapphire rods for 12 GHz
Diameter Height
d (mm) h (mm)
Short rod (TE resonator) 11,8 5,49
Long rod (TE resonator) 11,8 16,47
In order to minimize the measurement error in R of the superconductor films, both ends of the
s
sapphire rods shall be polished parallel to each other and perpendicular to the axis.
Specifications on the sapphire rods are described in 8.
7 Measurement procedure
7.1 Specimen preparation
From error estimation, the film diameter shall be about three times larger than that of the
sapphire rods. In this configuration, the error of R due to radiation loss can be neglected
s
comparing with the target precision of 20 %. The film thickness shall be about three times
larger than the London penetration depth at zero Kelvin.
Table 2 shows dimensions of the superconductor films recommended for the standard
sapphire rods of 11,8 mm in diameter.
Table 2 – Dimensions of superconductor film for 12 GHz
Standard dielectric rod Superconductor film
Material Diameter Diameter Thickness
′
ε
d (mm) d ′′′′ (mm) (μμμμm)
Sapphire 9,4 11,8 >40 ≅ 0,5
– 12 – 61788-7 IEC:2002(E)
7.2 Set-up
Set up the measurement equipment as shown in figure 4. All of the measurement apparatus,
standard sapphire rods, and superconductor films shall be kept in a clean and dry state as
high humidity may degrade the unloaded Q-value. The specimen and the measurement
apparatus shall be fixed in a temperature-controlled cryocooler. The specimen chamber shall
be generally evacuated. The temperatures of the superconductor films and standard sapphire
rods shall be measured by a diode thermometer, or a thermocouple. The temperatures of the
upper and lower superconductor films, and standard sapphire rods must be kept as close as
possible. This can be achieved by covering the measurement apparatus with aluminum foil, or
filling the specimen chamber with helium gas.
7.3 Measurement of reference level
The level of full transmission power (reference level) shall be measured first. Fix the output
power of the synthesized sweeper below 10 mW because the measurement accuracy
depends on the measuring signal level. Connect the reference line of semi-rigid cable
between the input and output connectors. Then, measure the transmission power level over
the entire measurement frequency and temperature range. The reference level can change
several decibels when temperature of the apparatus is changed from room temperature to the
lowest measurement temperature. Therefore, the temperature dependence of the reference
level must be taken into account.
7.4 Measurement of the standard sapphire rod for TE mode short-circuited
by two metal conductor plates
The resonance peak cannot be observed at room temperature because the superconductor
films are not in the superconducting state at that temperature. In order to know the resonant
frequency of TE or TE mode, the measurement using the combination of copper or
011 013
silver conducting plates and the standard sapphire rod shall be performed prior to the
measurements of the superconductor films. The resonant frequency of TE mode of the
standard sapphire rod can be measured as follows.
a) Connect the measurement apparatus between the input and output connectors (figure 5).
Insert the standard short sapphire rod near the centre of the conductor plates and adjust
the distance between the sapphire rod and each of the loops of the semi-rigid cables to be
equal to each other, so that this transmission-type resonator can be under-coupled
equally to both loops.
b) Put down the upper conductor plate gently to touch the top face of the rod. Be careful not
to damage the surface of the conductor plates by excessive pressure.
c) Find the TE mode resonance peak of this resonator on the display of the network
analyzer. As figure 6(a) shows, this mode can be detected as the second sharp peak from
the lower side of the frequency range.
d) Narrow the frequency span on the display so that only the resonance peak of TE mode
can be shown (figure 7). By changing the distance between the sapphire rod and the loops
of semi-rigid cables, adjust the insertion attenuation IA of this mode to be around 40 dB
from the reference level. Measure the resonant frequency f .
Metallic particulates on the sapphire rod have a significant impact on the measured tan δ. A
careful cleaning of the rods is rec
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.
Loading comments...