Material Measurement Basics - BDE ENSICAENchateign/enseig/dielectriques/HPdielmethod… ·...

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Material MeasurementBasics


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


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 =


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


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


"’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 =


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)

+

-


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.


Measurement Cycle

?Fixture

Software

?εµ

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Measurement Instruments

■ LCR Meters and Impedance Analyzers■ Impedance/Material Analyzer■ Network Analyzers


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


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.


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


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


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


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)


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


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


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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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


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


+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 =


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)


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 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


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


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


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


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=


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


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%


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


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


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


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>


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


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


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


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


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


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



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


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)


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


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


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


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



Cavity Fixture

HP 8752, 8753, 8719, 8720, 8722 or 8510

Software

Sample

Iris-coupled

end plates

Sample


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


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


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

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