material measurement basics - bde ensicaenchateign/enseig/dielectriques/hpdielmethod… ·...
TRANSCRIPT
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Material MeasurementBasics
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Agenda
■ Fundamentals■ LCR meters and Impedance Analyzers■ RF and MW Network Analyzer
◆ Transmission Measurements◆ Dielectric Probe Measurements◆ Cavity Resonator Measurements
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Objectives
◆ Provide basic education on dielectric measurements◆ Provide guidance in choosing the best measurement
technique for a given application◆ Give practical information for improving measurements
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Why make measurements?
Development ofnew materials
Controlling amanufacturingprocess
Incoming inspectionof materials
Shorter design cyclesHigher performanceReduced scrap
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Parallel Plate Capacitor (DC)
Capacitance with nodielectric (vacuum)
t
AC =0
0’’
C
Cr == εκ
Dielectric constant orpermittivity (real)
t
A
-+
-+
-+ -
+
-+
-+
-+-
+
+
-
V ’0κCC =
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Parallel Plate Capacitor (AC)
)’( 0 GCjVIII lc +=+= κω
C Gt
A
-+
-+
-+ -
+
-+
-+
-+-
+
+
-
V
κωκκω )()"’)(( 00 CjVjCjVI =−=
I
if "0κωCG =
then
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ED ε=
rεεεε 0* ==
Definition of electric displacement(electric flux density)
ε
mFx /1036
1 90
−≈π
ε
rε
Absolute permittivity or permittivity
Free space permittivity
Permittivity (electromagnetic fields)
Relative permittivity or dielectric constant
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Permittivity is complex
"’
0rrr jεεε
εεκ −===
storage loss
’rε Measure of how much energy from an external electric field is stored in the material
"rε Measure of how much dissipative or lossy a material is to an external field
Loss factor
Permittivity
The permittivity is often calleddielectric constant, but ischanging with frequency.
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Loss Tangent
Dissipation Factor Quality Factor
’
"tan
’
"
κκ
εεδ ==
r
r
CycleperStoredEnergy
CycleperLostEnergy
QD === 1
tanδ
D Q
rεεr”
’εr
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Inductor
R
L
Corematerial
Inductance of coil in free space
’0µLL =
0’
L
L=µ
0L
Real permeability
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Permeability is complex
"’
0rr jµµ
µµµ −==
storage loss
rµµµµ 0* ==µ
rµ
Absolute permeability
Relative permeability
mHx /104 70
−= πµ
Free space permeability
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"’rrr jµµµ −="’
rrr jεεε −=
Electromagnetic Field Interaction
Electric Magnetic
Permittivity
Dielectric Constant
Permeability
FieldsFields
STORAGE
LOSS
STORAGE
LOSS
MUT
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Dielectric Properties (at 3 GHz)
.0001 .001 .01 .1 1.00001
1
2
5
10
20
50
100
Wood
0%
10%
20%
Ice
Alcohol
Steak
Water Salt
Mylar
AirTeflon
Quartz
Alumina
TiO Water2
PC Board
Low Loss Lossy
’rε
’" /tan rr εεδ =
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Dielectric Mechanisms vs. Frequency
Dipolar
Atomic Electronic
103
106
109
1012
1015 f
+
-
-
+
+
-
VIRMW UV
+
-
Ionic
εr’
’’εr
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Relaxation Time τ
11 GHz
10
100
10 GHz 100 GHz
Time required for 1/e of a perturbed (aligned) systemto return to equilibrium (random)
εs’
’’εs
ε ’’’ε
cc fπωτ
2
11 ==
Water at 20o C (fc = 22 GHz)
Dipolar (orientation polarization)
+
-
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Cole-Cole Plots (Water)
34.9
34.9
23.79.14
3.25
1.74
9.14
4.6323.7
0.58
20 30 40 50 60 70 80 90100
40
10
20
30
0
Increasingf (GHz)
20 Co
60 Co
4.63
"rε
’rε
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The Cole-Cole Model
( ) αωτεεεε −
∞∞ +
−+=11 j
srd
sε∞ε
τfπω 2=
α
the DC value of dielectric constant
the infinite frequency dielectric constant
the relaxation width
the relaxation time constant
the angular frequency
The Cole-Cole model isused in determination ofuser defined standard forcoaxial dielectric probe.
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Measurement Cycle
?Fixture
Software
?εµ
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Measurement Instruments
■ LCR Meters and Impedance Analyzers■ Impedance/Material Analyzer■ Network Analyzers
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Auto-Balancing Bridge
V1
V2
H L
I 2
R 2
MUT
Fixture
2
21
2
1
V
RV
I
VZ ==
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LCR Meter/Impedance Analyzer
HP 4263B, 4284A, 4285A and 4278A LCR metersHP 4192A and 4194A impedance/gain-phase analyzers
■ 5 Hz to 40 MHz■ Measures impedance, phase, R, L, C, D, etc.■ High impedance measurement environment■ High resolution and accuracy■ Frequency
➜ single (LCR meter)➜ swept (impedance analyzer)
■ Simple and inexpensive
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Impedance/Material AnalyzerHP 4291A
■ 1 MHz to 1.8 GHz■ Calculates and Displays Material Parameters
(ε,µ) vs frequency, temperature■ Measure Impedance, phase, R, L, C, D, etc.■ High Resolution and Accuracy■ Ease of Use
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MW Frequency Concerns
Low frequency MW frequency
ComplexSimple
ExpensiveLow cost
Small wavelengthLarge wavelength
Transmission lineLumped element
vs.
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Network Analyzer
Source Receiver
Reflected Transmitted
MUT
Fixture
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Measurement CalibrationCalibration is always important, but at high frequencies
measurement errors can be more significant
■ Calibration eliminates systematic (stable, repeatable) errors,but not random errors
➝ noise, drift, or environment➝ temperature, humidity, pressure
■ Measurements more susceptible to small changes in system■ Minimize errors with good measurement practices
➝ visually inspect connectors for dirt/damage➝ minimize physical movement of test port cables
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Network Analyzer
300 kHz to 110 GHz
Measures reflection/transmission (magnitude and phase)
High accuracy
vs. frequency
50 ohm measurement environment
HP 8753, 8720 and 8510 family of network analyzers
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HP Instrument Summary
10 10 10
HP 4192A, 4194A, 4263B, LCR meters
Network
DCf (Hz)1 2 3 10 4 10 5 10 6 10 7 10 8 10 9 1010 1011
Impedance analyzers
analyzers
4284A, 4285A, 4278A
HP 8510C
HP 8720D
HP 8753E
HP 4291B Impedance/MaterialAnalyzer
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Measurement Techniques
■ Parallel Plate■ Coaxial probe■ Transmission line■ Free-space■ Resonant cavity
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Parallel Plate
10-50 mm< 10 mm
Liquids
tA
Cr
0
’
εε =
D=δtan
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LF Parallel Plate SystemLCR Meter or Impedance Analyzer (HP 4192A, 4194A, 4263B, 4284A, 4285A or 4287A)
LOGMA G
PHASE
DEL AY
SMITHCHART
POLAR
LINMA G
SWR
MO RE
START .300 000N MH Z
CH1 S11 1 U FS
Cor
Hid
HP 16451BDielectric Test Fixture
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LF Parallel Plate System (Liquid)
HP 16048A (Normal)PN 16452-616001 (High Temp.)
4TP
HP 16452ALiquid Test Fixture
LCR Meter or Impedance Analyzer (4194A, 4284A, 4285A)
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RF Parallel Plate System
LINE
4291AIMPEDANCE/MATERIAL ANALYZER
1MHz - 1.8GHz
O
.EntryOff
BackSpace
ACTIVE CHA NNEL
MEA SU RE MENT
SWE EP
INSTRU MENT ST ATE
ENT RY
MA RK ER
Start Stop
Cen ter Span
Rmt
G/n
M/
k/m
x1
Preset
Recall
Local
Save
System
Copy
Marker
Utili ty
Marker
Search
TriggerSourceSweep
CalBw/Avg
ScaleRef
Meas Format Disp lay
Ch 1 Ch 2
+30dBm Max 0V m Max
AVO ID ST ATICDISCH ARG E
HP 4291A RF Impedance/Material Analyzer
Test Head
HP HP 16143A DielectricMaterial Test Fixture
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LF Parallel Plate Summary
Relatively simple computationof εr from C and D
Inexpensive
Works well for thin sheets,PC boards, films, etc.
Frequency limitedto < 100 MHz
Does not provide µr
Accurate: typically±1% for εr’ , and5% ± 0.005 for tanδ
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RF Parallel Plate Summary
Automatic computationof εr from C and D
Frequency limited to1MHz to 1.8GHz
Sample must be flat,smooth sheet
Provides automatic µr
Works well for thin sheets,PC boards, films, etc.
Accurate: typically±8% for εr’ < 10 , and± 0.003 for tanδ
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Coaxial Probe
11
Solids
Liquids
Reflection(S )
rε11S
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Dielectric Probe SystemComputer
Network Analyzer
HP 85070BDielectric Probe
HP-IB
LOGMA G
PHASE
DEL AY
SMITHCHA
RT
POLAR
LINMA G
SWR
MO RE
START .300 000NMH Z
CH1 S11 1 UFS
Cor
Hid
HP Vectra PC (MS-DOS) or
HP 9000 Series 300 (HP BASIC) HP 8752, 8753, 8719, 8720, 8722 or 8510
HP 85070B Software(Included with probe kit)
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11
Reflection
(S )
Material assumptions:■ "infinite" thickness■ non-magnetic■ isotropic and homogeneous■ flat surface■ no air gaps
Method features▲ Broadband▲ Simple and convenient (Nondestructive)▲ Limited εr accuracy and tanδ low loss resolution▲ Best for liquids or semi-solids
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Higher Lower
Radiation
LY "rCεω rG’rCj εω
’rε "rε
’rε’rε
φ
flog
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Short User-definedstandard(usually water)
Open
Three term calibration (1-port)
Measure three known standards
Difference in predicted and actual value is used to correct measurement
Directivity
Tracking
Source match
corrects
1
1
=Γ=rε
1−=Γ
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Cable stability
Air gaps
Sample thickness
Minimize cable flexing
Allow time for cable to stabilize
Machine a flat sample face
Probe flatness ~ 100 µ inches
Recommended minimum thickness
( )mmtrε
20min =
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Remeasuring Air at Various Cable Positions
0.6
0.8
1.0
1.2
1.4
0 5 10 15 20
)(GHzf
’rε
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00e11e
10e
01e
Refresh CalibrationIf the perturbation is small, the change can be characterized
by the measurement of a single cal standard
= Perturbation term
= Directivity error
= Source match error
= Reflection tracking error
= Measured S
= Actual S
11
11
a
am cce
cceee
Γ∆∆−Γ∆∆+=Γ
011011
0110011000 1
mΓ
mΓ
aΓaΓ
00e
11e
10e01e
10c∆
01c∆10c∆ 01c∆
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Refresh Calibration StandardsPermittivity of Water at 55o C
0
20
40
60
80
0
20
40
60
80
0.1 1 10 100
Room Temp Cal Air RefreshShort Refresh 55 o C Cal
)(GHzf
’rε "rε
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+20%
+10%
+5%
NOM
-5%
-10%
-20%
Errors for Thin Materials
Measurements of Stacks of Paper
Thickness (mm)0 5 10 13 15 20
Foam-Backed
Metal-Backed
%-E
rror
r
tε
20min =min7
1tt =
06.0tan4.2’ == δεr
Paper
min21
tt =
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Coaxial Probe Typical Accuracy
20
18
16
14
12
10
8
6
4
2
0
0.20
0.18
0.16
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0.000 5 10 15 20
5
2
20
80
50
)(GHzf
(%)’rε δtan±80,50,20,5,2’=rε
GHzfrε
100max =
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Relative Measurements
2.0
2.5
3.0
3.5
4.0
0.1 1 10 100
Rexolite ProbeKynar Probe Kynar 7mm T/R Kynar-Rex + 2.54
)(GHzf
’rε
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Relative Measurements
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0.1 1 10 100
Rexolite ProbeKynar Probe Kynar 7mm T/R Kynar-Rex + 2.54
)(GHzf
"rε
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HP 85070B High-temperature dielectric probe kit
▲ 200 MHz to 20 GHz▲ Temperature range of -40 to +200o C
HP 85071B materials measurement software
HP 85070M Dielectric measurement system▲ probe▲ network analyzer▲ computer
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Coaxial Probe Summary
Convenient, easy to use
Little or no sample preparation
Nondestructive formany materials
Requires samplethickness of > 1 cm (typical
Solids must have a flat surface
Does not provide µr
Ideal for liquids or semisolids
Broad frequency range(.2-20 GHz depending on εr)
Limited accuracy in ε’r( + 5%) and low lossresolution ( + .05 in tanδ)
Not suited to high ε’rlow ε”r materials
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Transmission Line Technique
Waveguide
Coax
Material assumptions:■ sample fills fixture cross section■ no air gaps at fixture walls■ smooth, flat faces, perpendicular to long axis■ homogeneous
Method features:▲ Broadband - low end limited by practical sample length▲ Limited low loss resolution▲ Measures magnetic materials▲ Anisotropic materials can be measured in waveguide▲ Coaxial line supports planar TEM mode (free space)
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Transmission Line
Waveguide
Coax
l
Reflection
(S )11
Transmission
(S )21
rε
rµ
11S
22S
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Transmission Line SystemComputer Network Analyzer
HP-IB
LOGMA G
PHASE
DELAY
SMITHCHA
RTPOLA
R
LINMA G
SWR
MO RE
START .300 000NMH Z
CH1 S11 1 UFS
Cor
Hid
HP Vectra PC (MS-DOS) or
HP 9000 Series 300 (HP BASIC)
Transmission Line Fixture
(coaxial or waveguide)
HP 8752, 8753, 8719, 8720, 8722 or 8510
HP 85071BMaterials Measurement
Software
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Algorithm Measured OutputOptimumLength
Nicolson-Ross S11,S21,S12,S22 λg/4 εr and µr (PN 8510-3) (or S11,S21)
Precision (NIST) S11,S21,S12,S22 nλg/4 εr
Fast S11,S21,S12,S22 nλg/4 εr
(or S11,S21)
Short-circuited S11 λg/2 εr back
Arbitrary dielectric S11 λg/2 εr back
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Algorithm Best fit for
Nicolson-Ross Magnetic, short or lossy MUTs. Fastest computation speed.
Precision (NIST) Long, low-loss MUTs. Highest accuracy with no discontinuities.
Fast Long, low-loss MUTs Similar to Precision but faster and better for lossy MUTs
Short-circuited Liquids, powders back
Arbitrary dielectric Thin films back
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D
PTFE in WR-90 (l = 5.395 cm)
5.000
4.000
3.000
2.000
1.000
0.000
8.2 GHz 12.4 GHz
12
Precision (NIST) Algorithm
)(GHzf
’rε
Nicolson-Ross Precision (NIST)
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One-port reflection calibration (3 term error correction)
Full two-port calibration (12 term error correction)
Offset/Line standard doubles as sample holder
Open (offset short)/Short/Load (fixed, sliding, offset)
Open (offset short)/Short/Load (fixed, sliding, offset)/Thru
Thru/Reflect/Line (HP 8510 only)
Frequency response calibration
Open, short or thru only
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Fixed load
Sliding load
Offset load
D
D
D
Load
Offset
element
θ
LOffsetΓ
LΓ
LΓ
LΓ
Dm
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Thru
Reflect
Line
- Unknown high reflect
- Same response to Port 1 and 2
- Different in length than "Thru"
- Zero or non-zero length
- Reflectionless
Port 1 Port 2
Port 2
Port 2
Port 1
Port 1
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Fewer known standards required
Simple standards (especially for non-coaxial media)
Highest precision
Residual
Errors
Fixed
Load
Sliding
Load
Offset
Load TRL
Directivity
Match
Tracking
-40 dB
-35 dB
0.1 dB
-52 dB
-41 dB
0.047 dB
-60 dB
-42 dB
0.035 dB
-60 dB
-60 dB
0 dB
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1. Calibrate in a known connector type
Remove mismatches or re-reflections
Calibrate when no calibration standards are available
2. Connect cable or adapters
3. Connect SHORT
Apply time domain gate to SHORT response
4. Normalize with TDR gate ON
Add phase offset of 180 degrees
5. For transmission, normalize to THRU response
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Time Domain Gating
Time domain response Frequency domain response
UngatedGated
Ungated
Gated
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Sample Length
Avoid drop-outs in Nicolson-Ross algorithm
Long samples may create multiple roots
S21 phase shift >> S21 uncertainty (approx. 20o )
Maximum lengthMinimum length
Optimum length for low loss materials
For Nicolson-Ross: For Precision or Fast:
Sample loss
>
360
20min gL λ
2maxgL
λ<
( )max4 11 == SL gλ ( )max
2 21 == Sn
L gλ
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Wavelength Equations
Wavelength of free space
Waveguide wavelength
Phase shift
= cutoff frequency for waveguide
)(
3000 GHzinf
mm
f
c ==λ
c
rr
g
λλµε
λ1
1
0
’’
−
=
( )o
g
L360
λφ =∆
cλ
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Precision/Fast Algorithms
Iterative technique avoids drop-outs in long samples
Solution converges differently depending on initial seed
- ambiguity in number of compete wavelengths in material
0
1
2
3
4
5
9 10 11 12
Seed = 2.0
Seed = 2.5
Seed = 3.0
Seed = 3.5
Separation between solutions decreases with longer samples
)(GHzf
’rε 10.16 cm Rexolite in X band
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Choosing Initial Seed Values
Initial seed value equation for coaxialtransmission line (initial guess forwaveguide):
For waveguide, use initial guess intranscendental equation:
c = speed of light (vacuum)
L = sample length
f = frequency of S null
f = frequency of adjacent S null
f = cutoff frequency (waveguide)
11
112
1
c
May take
several
iterations
S11
f 2f 1
( )2
122
−
=ffL
crε
2
22
1
22
22
−−−
=
r
c
r
c
rf
ff
fL
c
εε
ε
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Use sample holder as THRU calibration standard (coaxial)
Include sample holder as part of Port 2 (waveguide)
Modify cal kit definition:
Port 2Port 1
Thru
Define: sample holder length = 0
c
Ldelayoffset
airrholder ε=
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Transmission Line Air Gaps
(Altschuler, 1963)
d1 d2 d3 d4
d b
aneglect gaps along a
D
dmc’’ εε =
D
bmc δδ tantan =
( )dbbD m −−= ’εwhere
1’
3
2’’
LL
L
mmc ε
εε−
=
+=
2
11tantanL
Lcmc εδδ
3
4
1
21 loglog
d
d
d
dL +=
2
32 log
d
dL =
1
43 log
d
dL =
where
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Typical Errors Caused By Air Gaps
Permittivity of material
High εr materials in coaxial lines = 20% to 50%
Size of transmission line
For εr = 10 and air gap = 0.25 mm (coaxial line)
Coaxial line dimensions Error
35%
14%
8%
4%
3.2%
1.7%
3.0 mm
7.0 mm
14.0 mm
25.0 mm
1.625 in
3.125 in
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Transmission Line Errors
Careful calibration
Air gaps betweenSample length
Use TRL or
Measure length precisely Use larger fixture
Focus on fit of center conductor (coaxial)
or on fit of broadband wall (waveguide)
Measure gap precisely and correct in software
Fill gap with conductive grease
Metalize sample sides
sample and fixture
Use good standards
time domain gating
Network
uncertaintyerrors
analyzer
Sources of error
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Transmission Line Typical Accuracy
For low loss, nonmagnetic, isotropic, rigid material
Requires precise sample machining (e.g. 0.03 mm)
Reported 2-4 times better accuracy with no air gaps
31’ −=rε 103’ −=rε 3010’ −=rεCoaxial line 2% 5% 10%Waveguide 1% 3% 5%
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Coaxial Transmission Line FixturesHP coaxial transmission lines- Type-N, 7 mm, 3.5 mm and 2.4 mm
Damaskos square coaxial line- anisotropic or square periodic repeating samples
Damaskos coaxial line platform- "clam-shell" design in 1.5", 14 mm and 7 mm
Damaskos coaxial compactor- 1.5" short-backed fixture for powders and liquids
Inter-Continental Microwave materials measurement fixture- 7 mm mainframe and sample cells
Maury Microwave coaxial transmission lines- 14 mm, Type-N and 7 mm
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HP coaxial waveguide components
- X/P/K/R/Q/U/V/W 11644A calibration kits ( λ /4 line)
Flann Microwave waveguide fixtures
- X band cell with removeable top plate and gauging rods
Damaskos waveguide platform
- C/X/Ku band two-piece clamp design
Damaskos high temperature waveguide measurement system
- C band up to 1000o F
Maury Microwave waveguide sections
- R/D/S/E/G/F/C/H/X/M/P/N/K/U band straight sections
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Transmission Line Summary
Provides both εr and µr
Simple fixtures
Frequency limited to >100MHz (banded in waveguide)
Precise sample shape required(usually destructive)
Adaptable to "free space"
Broad frequency range(0.1-110 GHz)
Limited low loss resolution
Liquids and gases mustbe contained
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Free Space Technique
Material assumptions:■ large, flat, parallel-faced samples ( > 10λ)■ homogeneous
Method features:▲ Non-contacting, non-destructive▲ High frequency - low end limited by practical sample size▲ Useful for high temperature▲ Antenna polarization may be varied for anisotropic materials▲ Measures magnetic materials
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Free Space Methods
NRL arch
Reflection
S-parameter (reflection/transmission)
Cavity
Open (Fabry-Perot) resonator
RCS (Radar Cross Section)
Tunnel
Transmission
RCS
Tunnel
NRLArch
rε
rµ
11S
21S
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Measures how large the object looks to radar
Monostatic, bistatic, quasi-monostatic configurations
RCS (dBsm) = 10 log[RCS (m2)] = dB below a square meter
Sample
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NRL Arch
Small arch of constant radius
Metal surfaceSample
Measure reflection from sample compared to flat metal surface
Reflectivity
Dual polarization
horns
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Free Space TunnelSample
Transmit horn Receive horn
Complex tranmsission coefficient (magnitude and phase) yields εr
Antenna should be 2d2/λ from the sample to maintain a planar"far-field" wavefront (where d is the larger of the antenna or samplediameter)
λ
22d>
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Free Space S-parameter
Plane wave incident on homogeneous sample of infinite
Focussing lenses convert spherical waves to plane waves
transverse dimensions
To Port 1 ofnetworkanalyzer
MaterialSample
To Port 2 ofnetworkanalyzer
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Free Space High Temperature
Fibrous insulation virtually transparent to microwaves
Heating panels
Sample
Thermal insulation
Thermocouple
Furnace
No tolerance requirements on sample
Sample is easily thermally isolated
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Free Space Calibration
TRL/TRM 2-port calibration (HP 8510 or 8720)
Time domain gating eliminates multiple reflections
Correction factors for defocussing effect
- Thru: focal points are coincident
- Reflect: metal plate at focal point
- Line or Match: focal points separated by λ/4
Response and isolation calibration (transmission)
Response calibration (reflection)
or use absorber as a match
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Time Domain Response
Ungated
Gated
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TDR Gated Frequency Response
Gated
Ungated
Removes fine grain response caused by re-reflections
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Free Space Sources of Error
Sample
Non-planewave illumination
Accuracy/calibration of microwave receiver
Mechanical stabilty/alignment of sample and antennae
Quality of anechoic environment
- finite size
- contact with conducting backplane
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Free Space Typical Accuracy
Typical acccuracy
Difficult to measure loss of thin ( < 1λ) andlow loss ( tanδ < 0.01) samples
%51−±=rε 005.0tan ±<δ
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Free Space Fixtures
Damaskos free space arch measurement system
- angle of incidence varies from 10 to 60 degrees
HVS free space EM materials measurement system
- Focussing lenses maintain a plane "far-field" wavefront
- dual polarization horns
- Temperatures to +850o C
- 5.85 GHz to >40 GHz in six bands
- 2 to 18 GHz horns
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Open Resonator (Fabry-Perot)
OutputInput
Sample
Generates Gaussian beam TEM mode
Concavemirror
Plane
εr and tanδ are obtained from change in fc and Q
Hemispherical
mirror
Full Confocal
Sample
Concavemirror
Concavemirror
Accurate for low loss (tanδ < 0.01) homogeneous material
Input Output
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Open Resonator (Fabry-Perot)
Commonly used at high frequencies (mm-wave and above)
Not suited to high temperatures
- Cavity is sensitive to thermal effects
Sensitive to low loss and thin film materials
Large, flat, parallel faced samples
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Free Space SystemComputer Network Analyzer
HP-IB
LOGMA G
PHASE
DELAY
SMITHCHART
POLAR
LINMA G
SWR
MORE
START .300000N MHZ
CH1 S11 1U FS
Cor
Hid
HP Vectra PC (MS-DOS) or
HP 9000 Series 300 (HP BASIC)
Antennae
HP 85071B
HP 8752, 8753, 8719, 8720, 8722 or 8510
Materials Measurement
Software
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Free Space Summary
Noncontacting, oftennondestructive
● Sample not contained● Useful for high
temperatures● Remote sensing
Time domain gating caneliminate mismatch error
Special calibrationconsiderations
● Requires connectorlessstandards (TRL, LRM)● Tightly controlleddistance from antenna tosample
Requires large, flat, thin,parallel faced sample
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Resonant Cavity
RF Connector MUT
Support
f
Q
Q0
fC
f
QS
fS
rr or µεSample
Iris-coupled end plates
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Cavity Methods
Transmission line (waveguide) cavity
TE cavity01nResonator (absolute)
Cavity perturbation
Sample fills a significant portion of cavity volume.Exact theories applied to cavities for low lossmaterials.
Sample disturbs (without changing) fields in cavity.
Measure shift in resonant frequency and Q.f < 0.1% (recommended)
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TE Cavity
Small coupling apertures(to waveguide)
Helical wavegude
Electric field
Disc samplePiston for tuning
E
01n
2
λn◆ Sample diameter same as cavity, wavelengths thick◆ Helical waveguide prevents TM11 mode
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Transmission Line Cavity
Based on ASTM 2520
E-field
Sample
Iris-coupled
end plates
◆ Rectangular waveguide cavity propagates TE10n mode◆ Sample placed parallel to cavity E-field◆ Fibers may be inserted through a fused silica rod
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Cavity Perturbation Algorithm
Q
fsffc
sQ c
ASTM 2520 Method
For a vertical rod or bar sample inserted in aTE10n rectangular waveguide resonant cavity
empty cavity
sample inserted
s
−=
css
cr QQV
V 11
4"ε( )
ss
sccr fV
ffV
2’
−=ε
sampletheofvolumetheisVc
cavityemptytheofvolumetheisVs
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Harmonic Stripline Cavity
Permittivity
Permeability
E-field
H-field
maximum
maximumSample
Ground
Center conductor
plane
◆ Single frequency - Cavity size setsfundamental frequency(also resonates at integer multiples)
◆ Ideal for small, thin, rectangularsolid samples
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Cavity Sources of Error
◆ Network analyzer frequency resolution◆ Sample dimension uncertainty◆ Approximations in analysis
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Top Cavity Accuracy
Results from NIST TE01n Resonator Cavity
00002.0tan
%4.0%2.0’
±=±±=
δε tor
◆ Accuracy
◆ Dominant TE01n modes, all other modes attenuated >25 dB◆ Unloaded Q = 83,000◆ Temperature controlled to within + 0.1 Co
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Cavity Fixtures
■ HP waveguide components◆ X/P/K/R/Q/U/V/W 11644A calibration kits
(standard section)◆ ASTM standard D-2520◆
■ Damaskos harmonic stripline cavity system◆ 100, 250 and 500 MHz fundamentals
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Resonant Cavity SystemComputer Network Analyzer
HP-IB
LOGMA G
PHASE
DELAY
SMITHCHART
POLAR
LINMA G
SWR
MORE
START .300000N MHZ
CH1 S11 1 UFS
Cor
Hid
HP Vectra PC (MS-DOS) or
HP 9000 Series 300 (HP BASIC)
Cavity Fixture
HP 8752, 8753, 8719, 8720, 8722 or 8510
Software
Sample
Iris-coupled
end plates
Sample
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Cavity Summary
Very accurate
Very sensitive to low loss(to 10-6 for some cavities)
Does not providebroadbandfrequency data
Analysis may becomplex
Precise sample shaperequired (usuallydestructive)
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Summary of Techniques
Parallel
Plate Fabry-Perot
Frequency
Loss
Free Space
Open ResonatorResonant Cavity
Coaxial
Probe
MicrowaveRF Millimeter-waveLow frequency
High
Medium
Low
Transmission Line
50 MHz 20 GHz 40 GHz 60 GHz5 GHz
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Measurement Technique Summary
10 10 10
Parallel plate
DC
Frequency (Hz)
1 2 3 10 4 10 5 10 6 10 7 10 8 10 9 10 10 10 11
Coaxial Probe
TransmissionLine
Cavity
10 12
FreeSpace
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Summary of Techniques
Parallel Plate
Coaxial Probe
Transmission Line
Resonant Cavity
Free Space
Best for low frequencies; thin, flat sheets
Accurate
Best for lossy MUTs; liquids or semi-solids
Broadband, convenient, non-destructive
Best for lossy MUTs; machineable solids
Broadband
Best for low loss MUTs; small samples
Accurate
Best for high temperatures; large, flat samples
Non-contacting
rr and µε
rε
rr and µε
rε
rr and µε
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HP Instruments and Fixtures
10Hz 100Hz 1kHz 10kHz 100kHz 1MHz 10MHz 100MHz 1GHz 10GHz 100GHz
HP 8510C
HP 8720C
HP 8753C
HP 85070B
HP 85071B
HP 4192A, 4194A, 4263A, 4284A, 4285A, 4278A
HP 16451B Dielectric test fixture
Dielectric probe
Transmission line software
LCR meters/impedance analyzers
Network analyzers
DC
HP 16452A Liquid test fixture
HP 4291A Impedance/Material Analyzer
HP 16143A Dielectric material test fixture
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Which Technique is Best?
It depends on:
■ Frequency range■ Expected value of εr and µr■ Required measurement accuracy■ Material properties (i.e., homogeneous, isotropic)■ Form of material (i.e., liquid, powder, solid, sheet)■ Sample size restrictions■ Destructive or nondestructive■ Contacting or noncontacting■ Temperature■ Cost■ And more . . .
1
Dielectric Mechanisms vs. Frequency
Dipolar
Atomic Electronic
103
106
109
1012
1015 f
+
-
-
+
+
-
VIRMW UV
+
-
Ionic
εr’
’’εr