A Handbook on Electromagnetic Shielding Materials and Performance

Table of contents :
Table of contents :
Page No.
ACKNOWLEDGEMENT iid
OTHER BOOKS BY THE AUTHOR i1d
PREFACE iv
TABLE OF CONTENTS vi
LIST OF TABLES viii
LIST OF ILLUSTRATIONS ix
LIST OF SYMBOLS AND ABBREVIATIONS Xiii

CHAPTER 1 SHIELDING THEORY
1.1 FIELD THEQORY 1.1

1.2 WAVE IMPEDANCE 1.5

1.3 METAL IMPEDANCE 1.8
1.3.1 Barrier Impedance of Metals (t >> §) 1.9
1.3.2 Barrier Impedance of Metals (t < 3¢) 1.11

1.4 SHIELDING EFFECTIVENESS 1.14
1.4.1 Absorption Loss 1.19
1.4.2 Reflection Loss 1.19
1.4.3 Re-Reflection Correction 1.29
1.4.4 Total Losses for K »> 1) 1.29
1.4.5 Low-Frequency Magnetic Shielding Effectiveness 1.32
1.4.6 Performance Degradation 1.35

CHAPTER 2 SHIELDING MATERIALS AND TESTING
2.1 SHIELDING MATERIALS 2.1
2.1.1 Homogeneous Metals 2.1
2.1.2 Pseudo-Homogeneous Metals 2.10
2.1.3 Small-Aperture Metals 2.19
2.1.4 Shielded Optical Display Windows 2.24
2.2 SHIELDING DENSITY FOR WEIGHT-SENSITIVE APPLICATIONS 2.28
2.3 MIL-STD-285 2.34

CHAPTER 3 APPLICATIONS AND EXAMPLES
3.1 HOW TO USE THE DESIGN GRAPHS 3.1
3.2 ILLUSTRATIVE EXAMPLES
3.3 HP-65 PROGRAM FOR SHIELDING EFFECTIVENESS
3.3.1 User Program Instructions
3.3.2 I1lustrative Examples

CHAPTER4 REFERENCES
APPENDICES
APPENDIX A COPPER A T-A6
APPENDIX B MONEL B.1-B.6
APPENDIX C NICKEL C.1-C.6

APPENDIX D IRON D.1-D.6
APPENDIX E HYPERNICK E.1-E.6
APPENDIX F 78 Permalloy F.1-F.6
APPENDIX G HIGH PERMEABILITY G.1-G.6

INDEX

Citation preview

A HANDBOOK ON

ELECTROMAGNETIC SHIELDING MATERIALS AND PERFORMANCE By

Donald

DON

R.

WHITE

J.

White,

MSEE/PE

CONSULTANTS,

INC,

State Route 625 P.0. Box D Gainesville, Virginia

Phone: TLX:

22065

703-347-0030

89-9165

DWCI

(§}COpyright Second

GAIV

1980

Edition

All rights reserved. This book, or any thereof, may not be reproduced in any form the written permission of the publisher. Library Printed

of

Congress in

the

Catalog

United

Card

States

of

No.

parts without

75~16592

America

ACKNOWLEDGEMENT The author wishes to thank the many people who encouraged him to write this handbook on shielding. He expresses his appreciation to the individuals and companies who have furnished several of the illustrative figures, for which acknowledgements in this handbook have been made. The author expresses his appreciation to his wife Colleen and Muriel M. Moeller for their assistance in typing, and in the many facets of logistics involved in preparation of the manuscript; to

Luis

F.

Longoria

this

publication.

calculator

III

and

computations,

Jane

and

Backstrom

the

many

ii

for

others

their who

drafting,

have

helped

HP-65

produce

OTHER BOOKS PUBLISHED BY DWCI (1)

Electrical

published

1963,

published

(2) Volume 1971.

1970.

by

White

1,

Pilters-Synthesis,

Electromagnetics,

Eleotrical

Noise

{3) Volume 2, Electromagnetic and Procedures; published 1974. Methods

and

(4) Volume 3, Electromagnetic Technigques; published 1973,

(5) Volume &, Electromagnetic and Systems; published 1971, Techniques; Stendards,

Interference

Test

Instruments

Interference

Specifications,

(8)

A Glossary

(9)

Mertel,

Series;

Electromagnetic

published

II

Noise,

(11) Volume

1979,

Herbert

K.,

published

1978.

M., EMC

Abbreviations,

Intermational

Regulations,

Volume

I of

mmd

the

and Symbols; National

Radio

Multi-Volume

EMC

Spectrum Management Techniques, Encyclopedia Series; published

Herman, John R., Electromagnetic Ambients and Mon-Made III of the Multi-Volume EMC Encyclopedia Series;

{12) H;rl:, William Lightning Protection, Volume Series; published 1979, (13)

V of

1975.

of Aeromyms,

(10) Jansky, Donald of the Multi-Volume

Volume

the

Keiser,

C. and Malone, Edward W., Lightning and IV of the Multi-Volume EMC Encyclopedia

Bernhard

Multi~Volume

(14)

Feher,

{15)

Gard,

E.,

EMC

Kamilo,

Electronies,

published

1979.

{(16) White, (EMC Design (17)

Volume

Michael

Volume

in Aerospace

Series;

Systems,

published

1979

Digital Modulation Techniques in an IX

F.,

of

the

Multi-Volume

Flectromagnetic

X of

EMC

Russell

V.,

the Multi-Volume

e e e

1980,

EMI

Ency-

Interference

the Multi-Volume

Control

Control

EMC Encyclopedia

Donald R. J., EMI Control Methodology Synthesis); published 1978,

Carstensen,

XXIV of

EMI Control

Encyclopedia

Interference Environment, Volume clopedia Series; published 1977,

published

Control

6,

Encyclopedia

Ships,

Compatibility

Volume

Interference

Procedures

Test Methods

(7)

Frequency

Series;

Interference

Prediction

1971.

in Medical

Specificatioms;

Interference

published

Volume

EMI

December

5, Electromagretic 1972.

and Regulations;

published

and

and Applications;

Reprinted

{6) Volume published

Inc.

1977,

Design

Inc.

in

EMC Encyclopedia

Boats

and

and

Series;

PREFACE There

exists

substantial

material

in

the

literature

on

the

subject

of electromagnetic shielding., Chap. 4 presents many references, For either an individual who has only recently been introduced to shielding or to a design engineer, however, much of the literature appears to be either confusing or poorly organized for design use. Missing in the literature are a series of useful design graphs including all the principal variables presented in a clear, understandable manner. Thus, this handbook on Shielding was conceived to f£ill these voids, and EMC and ness and

This handbook does not cover the topics of where and when to shield, where to ground a shield. These topics are covered in Vol. 3 of the Handbook Series, Rather, this handbook explains shielding theory performance and presents many design graphs of shielding effective-~ vs frequency as a function of shield metal and its characteristics, E and H-fields and plane waves,

Regarding the impedance of the fields (E, H, literature and manufacturers' data are often very ample, since the wave and circult impedance which

interlocked

and

since

a circuit

impedance

is not

or plane waves), tiwe misleading. For exproduced the field .are

infinite,

E-field

shielding effectiveness data are generally optimistic (toco high) relative to actual performance, In a converse manner, H-field shielding effectiveness data are pessimistic (too low) since a magnetic source circuit impedance is not zero. This handbook clarifies and quantifies these points, Another example of possibly misleading information is the use of MIL-STD~285 to measure and report the shielding effectiveness of test items to E and H~fields. The reference test distance per MIL~STD-285 is

one

foot

(0.305

meters).

Thus,

for

installations

located

in

the

near field which are greater than one foot from an interfering source, actual E-field shielding performance will be less and H-field performance will be greater than that reported by MIL-S5TD-285 measurements. The converse applies for application distances between sources and metal barriers which are less than one foot away as illustrated in this handbook., The discussions and design data on shielding effectiveness in this handbook are not restricted to homogeneous metals. In fact no real life and useful shielded compartment, box, cabinet, or room is homogen-— eous since usually many penetrations of a six-sided shield configuration are necessary. Techniques used to reinstate the integrity of a shielded enclosure are discussed in Vol. 3 of the EMC Handbook Series, Shielding materials and performance of non-homogeneous metals are discussed in this handbook on Shielding, Some examples are pseudo-homogeneous shields made from metal deposition and flame-spray processes. Shields made of small-aperture metals are also presented. Examples include screens,

iv

PREFACE wire

meshes,

discussed

cable

herein

braids

together

and

with

metalized

design

textiles,

data.

all

of

which

are

The appendices of this handbook are perhaps the most important of all material presented. They contain 42 pages of design shielding effectiveness graphs for several metals whose thicknesses range from 0.0001 mil (2.54 nm) to 1 inch (2.54 cm). For both near and farfield calculations and associated frequencies, the design graphs cover source~to-metal distances ranging from 10 cm to 10 km. Frequency coverage is from 10 Hz to 30 GHz. All data were run-off on the HP-65 programmable calculator. For those who have an HP-65, the program is presented so that they can develop and use their owm magnetic card. There also exist many design graphs other than direct shielding effectiveness which the reader should find useful. The author of this handbook invites the user to communicate him. He especially invites comments, questions, or requests for further elucidation.

December 1975 Germantown, Maryland January 1980 Gainesville,

Virginia

USA

USA

Donald

R.

Second

J.

with

White

Edition

TABLE OF CONTENTS ELECTROMAGNETIC SHIELDING MATERIALS AND PERFORMANCE Page No. iii iti iv vi viii ix xiii

ACKNOWLEDGEMENT OTHER BOOKS BY THE AUTHOR PREFACE TABLE OF CONTENTS LIST OF TABLES LIST OF ILLUSTRATIONS LIST OF SYMBOLS AND ABBREVIATIONS

CHAPTER 1 SHIELDING THEORY 1.1 FIELD THEORY 1.2

WAVE

1.3

METAL

IMPEDANCE

1.3.1 1.3.2

Barrier Barrier

1.4

IMPEDANCE

SHIELDING oM

CHAPTER 2 2.1

Losses

Low-Frequency Performance

for K >> 1) Magnetic

Degradation

Shielding

Effectiveness

1.35

SHIELDING MATERIALS AND TESTING

0N

o

2.1.1 1 el

(t >> §) (t < 3s)

EFFECTIVENESS

Total

SHIELDING MM

of Metals of Metals

Absorption Loss Reflection Loss Re~Reflection Correction

OB

et gt e P

et st sk sl s e e b s

4.1

Impedance Impedance

2.1

MATERIALS

Homogeneous Metals Pseudo-Homogeneous Metals Small-Aperture Metals Shielded Optical Display Windows

2.2

SHIELDING

2.3

MIL-STD-285

DENSITY

FOR WEIGHT-SENSITIVE

2.1 2.10 2.19 2.24 APPLICATIONS

2.28 2.34

CHAPTER 3 APPLICATIONS AND EXAVPLES 3.1 HOW TO USE THE DESIGN GRAPHS vi

3.1

TasLE oF CONTENTS 3.2

ILLUSTRATIVE

3.3

HP-65 3.3.1 3.3.2

EXAMPLES

PROGRAM

FOR SHIELDING

User Program Illustrative

EFFECTIVENESS

Instructions Examples

CHAPTER 4

REFERENCES

APPENDICES APPENDIX A

COPPER

A.1-A.6

APPENDIX

B

MONEL

B.1-B.6

APPENDIX

C

NICKEL

C.1-C.6

APPENDIX

D

IRON

D.1-D.6

APPENDIX

E

HYPERNICK

E.1-E.6

APPENDIX

F

78

F.1-F.6

APPENDIX

G

HIGH

Permalloy

PERMEABILITY

G.1-G.6

INDEX

vii

LIST OF TABLES Page

CHAPTER 2

SHIELDING MATERIALS AND TESTING

2.1

Relative

2.2

Weight per Unit Area Some ietals

2.3

Applicable

2.4

Relative Thickness and Weights of Some Metals for Yielding the Same Shielding Effectiveness

CHAPTER 3

Metals

Conductivity

2.19

Line

and

Permeability

of

per Unit Thickness

Selection

for

Use

in

Fia,

APPLICATIONS AND EXAMPLES

3.1

Definition of Metal Class Based on Permeability and Conductivity Relative to Copper

3.2

Metal Use

3.3

Applicable

3.4

HP-65

Class

Specified Steps

for Choice Appendix Distance

Shielding

of Appendix

Design

Graph

Effectiveness

viii

to for

Program

of

No.

LIST OF ILLUSTRATIONS CHAPTER 1 Fig.

Title

No.

1 .1 1 .2 -

SHIELDING THEORY

.3 4 5

Electric-Field

Strength

vs.

Wave

as a Function

Page

Source

Conceptual ITlustration of Source Type and Distance

Field

Wave

Circuit

Impedance Impedance

Surface

for

Impedance

Saveral

and Skin

vs. Frequency Barrier Metal Impedance

Assuming

of Source

in

Haves Geometry

.10 11 12 13 .14 .15 .16 17 .18 19 .20

CHAPTER 2 2.1

2.2

Shielding

Absorption Copper Abscrption Aluminum Absorption Brass Absorption Beryllium Absorption Monel

Absorption

Iron Absorption Stainless

of Shielding

of Metal

Barrier

Iron vs. Ratios

in

Metals

Expression

Phenomena

Used

Effectiveness

Distance

Impedances

Zp

Surface Impedance of Copper and and Skin Depth in Units of t/§

Representation

vs.

Deptl: of Various

Error

t/s

Distance

Strengths

Freguency

for

Plane

Explaining

Loss

vs.

Freguency

and

Thickness

for

Loss

vs.

Frequency

and

Thickness

for

Loss

vs.

Frequency

and

Thickness

for

Loss

vs,

Frequency

and

Thickness

for

Loss

vs.

Frequency

and

Thickness

for

Loss

vs.

Frequency

and Thickness

for

Loss vs., Steel

Frequency

and

Thickness

for

and Thickness

for

Absorption Loss vs. Frequency High-Permeable Metals Re-Reflection

Correction

Absorption Loss Shielding Effectiveness

vs.

vs.

VSWR

and

SHIELDING MATERIALS AND TESTING Curve

(Solid)

Material

Metal-to-Emission

Distance and Surface Resistances Low Frequency, Shielding Effectiveness Fields

Magnetization

by

to Magnetic

and Hysteresis

Loop

Some Important Magnetic Quantities are I1lustrated Permeability Curves of Iron, with u Plotted Against H ard B. I and B-H are aiso used as Abscissae ix

.10 12 .13 .16 .16 .20 21 .22 .23 .24 .25 .26 .27 .30 .33 .34

Wire

for

Frequency

for

APPENDIX A

Correction

Thickness

MIL-STD-285

COPPER

and

in Shielding Results

of Tkm

Weight

vs.

Effectiveness

to Convert

to Another

Distance

Shielding

Effectiveness

of Copper

vs.

Frequency

for

A.2

Shielding

Effectiveness

of Copper

vs.

Frequency

for

vs.

Frequency

for

vs.

Frequency

for

vs.

Frequency

for

vs.

Frequency

for

A4

A.5 A.6

APPENDIX B

Shielding

Effectiveness

of 1m Copper of 10m Copper of 100m

of Copper

Source~to-Metal Distance of 1km Shielding Effectiveness of Copper

Source-to-Metal

MONEL

Distance

of 10km

B.1

Shielding

Effectiveness

of Monel

vs.

Frequency

for

B.2

Shielding

Effectiveness

of Monel

vs.

Frequency

for

B.3

Shielding Effectiveness of Monel Source-to-Metal Distance of 10m Shielding Effectiveness of Monel

vs.

Frequency

for

vs.

Frequency

for

B.4

Source~to-Metal

Distance

Source~to-Metal

Distance

PR

owNoo

~nN n

I

Source-to-Metal Distance Shielding Effectiveness of Source-to-Metal Distance Shielding Effectiveness of Source-to-Metal Distance

x>

A.3

Distance

>

Al

Source-to-Metal

ny ~N

Frequency

N

Aluminum

Distance

N

Source-to-Shield

of 10cm of 1m

I»

N

.19 .20

to Plane

Light Transmission of Conductive Glass Shielding Effectiveness of Gold vs. Frequency Source-to-Shield Distance of Im Shielding Effectiveness of Gold vs.

MMM

Gun

of Screen

[AS AN

Metallizing

W

Spray

Effectiveness

I

NN

Frequency

o

Flame

Shielding Waves

NP

vs.

Conductive Cecating on Interior of Plastic Equipment Enclosure Conductive Coatings for Both EMI and Static Bleed Functions Flame Spray Wire Metallizing Gun Thermo Spray, Metal Powder Metallizing Gun Plasma

MR

Permeability

Retative Permeability vs. Magnetic-Flux Density Surface Resistance of Copper vs. Volume Resistivity for Various Metal Thicknesses Conductivity Relative to Copper vs. Surface Resistances

o

Relative

N

Minor Hysteresis Loops Shown on Magnetization Curve Portrayal of Real World Situation

>

—t

N ‘.,

n .

™~ -

W

.

~n

O

PN .

NOUIE

NN «

W

™

LisT oF ILLUSTRATIONS

LisT oF ILLUSTRATIONS

of Monel

10km

vs.

NICKEL

for

Frequency

for

vs.

Frequency

for

€.3

Shielding Effectiveness of Nickel Source-to-Metal Distance of Im Shielding Effectiveness of Nickel

vs.

Frequency

for

C.4

Shielding

Effectiveness

of Nickel

vs.

Frequency

for

C.5

Shielding

Effectivenass

of Nickel

vs.

Frequency

for

vs.

Frequency

for

D.3

D.4 D.5

D.6

APPENDIX E E.1

£.2 E.3 E.4 E.5 E.6

OO

N

Source-to-Metal Distance of 1km Shielding Effectiveness of Nickel Source-~to-Metal Distance of 10km

W

100m

s

of

IRON Source-to-Metal Distance of Im Shielding Effectiveness of Iron vs. Source-to-Metal Distance of 10m

Frequency

for

Frequency

for

Source-to-Metal Distance of 100m Shielding Effectiveness of Iron vs. Source-to-Metal Distance of lkm

Frequency

for

Frequency

for

Frequency

for

Shielding

Shielding

Effectiveness

Effectiveness

Effedtiveness

Source-to~Metal

Distance

of Iron

of

Iron

of Iron of

vs.

for

vs.

vs.

10km

O

Shielding

Frequency

o

Shielding Effectiveness of Iron vs. Source-to-Metal Distance of 10cm

HYPERNICK

Shielding Effectiveness of Hypernick vs. for Source-to-Metal Distance of 10cm Shielding Effectiveness of Hypernick vs.

Frequency

Shielding Effectiveness of Hypernick for Source-to-Metal Distance of 10m Shielding Effectiveness of Hypernick for Source-to-Metal Distance of 100m Shielding Effectiveness of Hypernick for Source-to-Metal Distance of 1km Shielding Effectiveness of Hypernick

vs.

Frequency

vs.

Frequency

vs.

Frequency

vs.

Frequency

for Source-to-Metal

for Source-to-Metal

Distance

Distance

xi

of Im

of 10km

N

D.2

Distance

10m

W

0.1

Source-~to-Metal

of

o

APPENDIX D

Distance

B

C.6

Source-to~Metal

]

vs.

C.2

Shielding Effectiveness of Nickel Source-to-Metal Distance of 10cm

Frequency

Sy

of

O

Distance

Gy

C.1

Effectiveness

Source-to-Metal

for

Fregquency

N

APPENDIX C

Shielding

Freguency

W B YN

B.6

Source-to-Metal Distance of 100m Shielding Effectiveness of Monel vs. Source~to-Metal Distance of lkm

mooomM

B.5

LisT oF ILLUSTRATIONS

APPENDIX F F.1

F.2 F.3 F.4 F.5 F.6

APPENDIX G

78 PERMALLOY

Shielding Effectiveness of 78 Permalloy vs. Frequency for Source-to-Metal Distance of 10cm Shielding Effectiveness of 78 Permalloy vs. Fre-

quency for Source-to-Metal Distance of Im Shielding Effectiveness of 78 Permalloy vs. quency for Source-to-Metal Distance of 10m

Fre-

Shielding Effectiveness of 78 Permalloy vs. Frequency for Source-to-Metal Distance of 100m

Shielding Effectiveness of 78 Permalloy vs. quency for Source-to-Metal Distance of 1km Shielding Effectiveness of 78 Permalloy vs.

quency

for Source-to-Metal

HIGH PERMEABILITY

Shielding

G.2 G.3

Shielding Effectiveness of High Permeability vs. Frequency for Source-to-Metal Distance of Im Shielding Effectiveness of High Permeability vs.

G.4

Shielding

G.5 G.6

Frequency

for

for

of High

of 10km

Source-to-Metal

Source-to-Metal

Effectiveness

of High

Permeability

Fre-

G.1

Frequency

Effectiveness

Distance

Fre-

Distance

Distance

of

of

Permeability

vs.

10cm

10m

vs.

Frequency for Source-to-Metal Distance of 100m Shielding Effectiveness of High Permeability vs. Frequency for Source-to-Metal Distance of Tkm

Shielding Effectiveness of High Permeability vs. Frequency for Source-to-Metal Distance of 10km

xii

F.1 F.2 F.3 F.4 F.5 F.6

G.1 G.2 G.3 G.4 G.5 G.6

LIST OF SYMBOLS AND ABBREVIATIONS dB dB

absorption

loss

re-reflection velocity

of

cm

centimeter

Cu

copper

dB

decibel

=

Napierian

in

dB

loss

in

electromagnetic =

(.01

0.1

Bel

base

=

2]

electric~field frequency

dB

in

meter

=

=

10

wave

in

0.3937

air

=

1//ue

=

3x108m/sec

inches

loglo(power

ratio)

2.718

strength

in

volts/meter

in

amperes/meter

Hertz

frequency

in MHz

magnetic~field current

in

strength

amperes

imaginary

operator

3/2rr

E

for

=

fields;

angle

7/2 =

90

degrees

2ur/ix

for

H

fields;

=

1

for

plane

W

wave-to-metal

B

O

e

oom

MHz

f

ty

iron

meter

=

mil

0.001

ioch

=

2.54x10

millimeter

=

0.1

100

impedance cm

=

1000

cm

=

ratio,

Z W /Zm = VSWR

mm

=

39.37

cm

=

25.4

0.001

inches

for

=

3.28

39.37

mils

K 2 1 feet

um

meter

=

nanometer = 10 °m = 10 °mm = 10 um = 39.37x107° mils distance

from

EMI

distance

r

meters

shielding

effectiveness

reflection

metal time

in

emission

loss

in

dB

source

(loss) (excludes

in

to

metal

barrier

dB

re-reflection

thickness in

ratio

seconds

of

metal-thickness

voltage

in

voltage

standing

impedance

to

skin-depth

volts in

wave

ratio

ohms

barrier

metal

impedance,

circuit

impedance

in

Zm

ohms

xiid

for

any

t/8

ratio

loss)

waves

impedance

of metal

for

plane-wave

impedance impedance

t/§

>»

1

= Vuoleo

= 120w

= 377

ohms

N

E/H

R

attenuation

e

phase


>

1,

= ZoA/2mr. This

field,

i.,e.,

is

= 377 ohms.

> A/2m (far-field conditions), only the (1.3) is significant*. For this condition

(plane waves) and both Ep and Hy are in directional quadrature,

Eg/Hy

f = ¢/

1 in the electric-field and the of either sine or cosine terms

this corresponds to the transition-field the near field (first term of equations)

Eqs.

A

measuring

about

the multiplier, A/2nr = terms, all coefficients

equal.

D>

both

a small

rather

Zo

since

A/2mr

a high-impedance

It

is

also

time

phase

straight a small

the

wire

wire

and

or

loop

exhibiting low-circuit impedance, the first term appearing in Egqs. (1.1) and (1.2) would vanish, and a similar first term would appear in Eq. (1.3). For this condition, the wave impedance in the near field, Eg/Hy = Zo2nr/A. Note that the wave impedance is now > 1, i,e.,

is

low

called

relative

to

Zg,

a magnetic

the

field

plane~wave

or

a low-impedance

(radiation)

field,

impedance.

Fig. 1.1 illustrates the above first three observations (#1, 2, and 3) for the amplitude of each of the electric-field terms in Eq. (1.1). Note that the quasi-stationary field is the largest term in the

near

*

E,

field

and

the

is dropped

induction

from

further

term

is

next

discussion

largest,

here.

whereas,

the

F1eLp THeoRY

A

1000

2.3

BSoou7

Condition:

1

Doublet

2 or Small

3 Wire

5 in

7

10

60

Which D 1 for

r,

from

Summing

= E/H

source-to-metal

barrier

= Wlu/e

= 377k

up,

= kZ,

constant-current

and

r

(1.9)

or=—31 27 —

(1.10) *

Zy2mr

1

3

ZOZflr X

ohms., To the extent ion line impedances,

impedance

>

(1.11) Zc

(1.12)

to exist

when

r

\m = frequency in Hz

Zc z Zo

£

2%,

Eqs. (1.8) to (1.12) are plotted in Fig., 1.4 for including common tramnsmission-line impedances of

where,

to

The development of a discrete relation between circuit, Z., and Zy, impedance in the near field is beyond the scope of this handHowever, the following mathematical relations are suggested and

for

wave

rise

and use

in MHz

Z. 600

common transmisshigh or very low

to present Egs. than wavelength,

(1.13) (1.14)

Sec. 1.2

Wave IMPEDANCE

£3 10k

ey 6’70@

(&7

:

120

Conditions

fe~py

=

100 80

€lq

£

g 1k

in

héyés

Far-Fie

3 @

g

160

g

10

—

5

e-\(\

60

ons

S

40

’C'\c’j

T

e

y e

20

1 1

0

Near-Field .001

Figure

.003 1.4

.01

Distance

- Wave fMHz

Conditions

.03

from Source

Impedance

for

frequency

in

=

Ap = wavelength C = velocity Egqs.

(1.4)

High-Impedance

through Circuit

of

T

Circuit

in

near

light

in

-20

Impedances

air

field:

ZoA e

——

=

18,000

;—%———-

ohms

(1.15)

MHz

field: Zy2mr

7'9rmeHz

ohms

(1.16)

conditions:

z, = 120w In

10

become:

Zw == Far~field

of r = X\/2n

Circuit

3

MHz

m

Low-Impedance

1

in Units

Several

then

near

Zw

.3

in meters

(1.7) in

.

terms

of

the

more

general

= 377

ohms

conditions

1.7

dBQ

100k

L

Near-Field

(1.17) of

any

circuit

impedance

Impedance

-

Wy

Wave

M

Sec, 1.3 presented is:

METAL IMPEDANCE in Eqs.

(1.8)

through

(1.12),

Zw 2 l8,000/rmf ® 2., =

The

ing

foregoing

relations

presented

22z,

2 7.9rmfMHZ

(1.19)

ZC

(1.20)

will

be used

2>

in interpreting

the

appendices.

All

the

homogeneous

intrinsic

materials

impedance

of

are

characterized

the

where,

w = 27f

shield-

i

=

permeability

of

the material

permeability

My

= permeability

of

material

relative

¢ = conductivity

of

material

in

air,

intrinsic

wave

Z, = E/H,

conductivity

impedance

the

of

material

approaches

is

= 4w x 10~7 to

henrys/meter

air

mhos/meter = g,€,

of air = 1/367x10°) farads/meter

propagates

of Eq.

air

material

permitivity

= permitivity

electromagnetic

of

of

= yql,

= absolute

of the wave, For

wu

U,

€o = absolute

an

known

in Hz

€ = permitivity

ance

a quantity

radians

f = frequency

€,

by

material:

=

the

impedance (1.18)

7.91:meHz

the

wave

> lB,OOO/rmeHz

for

in

generated

PMETAL IMPEDANCE

as

As

Zc

18,000/rmfMHZ

7'9rmeHz’

effectiveness

1,3

for

, for

the

extremely

(1.21)

relative through

the

1.8

the

value

air material,

Zj

(see

small,

i,e,,

0t

terms

ohms/sq.

thickness

the

in

depth

(1.26)

of a metal is

flowing

is defined:

at

any

therein.

(1.27)

% As described later, the surface impedance is based on a metal thickness which is very much greater than the skin depth, t>>§, As the frequency approaches zero, G+«, and Z 0. *% Two skin depths = 86.5% and three skin depths = 95,0Z of the total current flow. For 99% of the current flow, 4.6 skin depths are required. Often a metal thickness, t, is considered to be adequate when, t>38.

1.9

METAL IMPEDANCE Sec. 1.3

o

m

ZH901

£0000

» 20000 % 2 L0000

S 50000 p

3

1000

2000°

ZHIE ZHIY

:

ZHAOOL

“sA s|ejay

ZHAOOE

on-finfm.,o;nvomoo.

ZN|

ZHNOL

snotdep 40 yidag

wd |

Kouanbaug oipey ZHAOE

0

Q€ < 3 SSaUNOLYL |elaw :uoLjdunssy

suyort o/ 7yt M ggp Uy

SLU P6E = SAUDUL YEE'D =

Aousnbauag

S

ZH0L

ZHIE

Aauanbau4

ULyS

ZHWE

e

pue

’

ZHOOE

aduepadw]

ZHWL

ZHOO |

adejung

ZHAOOL

- G|

000"

000

000*

ZHX00E

ZHOE

zHot

0

S0

0 .

a

g

B

© o

&

< -

3

8

™ =)

4L

..

O °

4

&

N

a4nbiyg

=

nwe

- =

o

3

-

=3

1.

the

left

edge

(1.52)

This field undergoes an attenuation in traversing the thickness the metal barrier which turns the associated loss into exothermic

1.5

of

Sec, 1.4

SHIELDING EFFECTIVENESS

INSIDE

Incident

’/,,Transm1tted Wave

Wave

Ey

Ey HZ

OUTSIDE WORLD

1.8

H,

Wave

Internal

t

- Representation

PR

of Shielding

-

/P

Omall-Pamle 2yt J/ /

|Phal1-Pamle

Wave

-2yt \

\

Outside

i old s Shielding Barrier

/

—t 1.9

Reflected

Wave

g "Yt

>

“P.mi€

oram

for

Plane

Waves

AlF -vt

(1'Oam)(1-pma)e Y >

Emerging Wave Beyond Shielding Barrier

ot

2ol

- JY

\pma(] Pam® o esm— e

(1-p,m) (1-0p5 )or €

-3yt

-

etc.

e———

Figure

\

ma

Wave ~o

e

Phenomena

Al e Metal Barrier 131 1-p am _ Pgmt—— | T T e (T-pype —

Incident

Attenuated

Incident

Reflected

Metal Barrier of Thickness, t Figure

OF ENCLOSURE

Propagation

- Geometry

Effectiveness

Metal

of

(See Text)

Thickness,

t——»

Constant y = o + jB Metal

Barrier

1 16

Used

> in

Explaining

Shielding

Y

Sec. 1.4 at

t. the

SHIELDING EFFECTIVENESS

The arriving right inside

field results in a lower edge of the barrier:

Pyg = Tyoett = e @H where,

=

propagation

constant

a

= attenuation

constant

phase

o

+

-

where,

Pra The

=

is:

(1.55)

is

“maFAR

=

the

when

1

1

-

€

pma(l

field,

jB

Tpp,

€

(l

effectiveness

y>>1,

_

at

the

inside

pam)

to

right

(1.54)

coefficient

= o YE(1_

QmaFAR

shielding

-yt

reflection

transmitted

FRE

tive number)

o~

= metal-to-air

relative

barrier

(1.53)

thickness

1RR

Eq.

=

The re-reflected relative field strength T'yr, of the metal-to-air barrier of Fig. 1.9 is:

edge

impinging

constant

t = metal

metal

strength

e”(“+j§)t(1~pam)

Y

8 =

field

the

right

-

pam)(l

(Eq.

(1.51)). just

outside

pma)

the

(1.55)

expressed

as

a gain

(a nega-

When the propagation constant is not significant, one or more round-trip re-reflections must be considered. For example, the rereflected field of Eq. (1.54) undergoes a second attenuation and phase shift in propagating back to the inside edge of the left metal-to-air interface of Fig, 1.9:

?LR The

barrier

re~reflected

is:

FLL

-

fRRa

field oz

vt

e

o2yt

styength,

F o R

T LL®

-2Yt

E-1

p

- pam)

pma(l

o

from

(1

—

o,

(1.56)

the

left

)

Finally, metal barrier

the is:

?LLQ

transmitted

TRT !

e

(l

-

o

=Ye _

3

=3yt Poa2

component

a)FfiR 1

—

e

1.7

-3yt

this re-reflected edge, the rela-

1 [l ®am 1

of

Tpp

o

2

a(l

inside

(1.537)

Undergoing a third attenuation and phase shift of field in arriving back at the inside face of the right tive field strength, Ipp, becomes:

"o ?AR

edge

(1.58)

to

-—

0

the

)(l

right

v

0 a)

ocutside

the

(1.59)

Sec, 1.4 Since

the

SHIELDING EFFECTIVENESS

the

direct

TT

=

re-reflected

field

transmitted

field

e Yt(l—pam)(l—pma){?

component

of +

Eq.

of

(1.55),

e zYtpéa

Eq.

(1.59)

they

+ e 4Ytpl’a

First

The

terms

infinity

in

of

by writing becomes:

the bracket

constitute

re-reflections).

this

series

in

The

terms

of

an

its

"".]

(1.60)

series

reciprocal.

(i.e.,

can

Thus,

be

an

simplified

Eq.

Y )

(1.61)

therein:

_

_=

—otf2K

2

-at 4K ~W

[l

the air(1.51)

K-1Y2 -2yt|™!

(m) (‘f:fi)[l - (Efi.’) °

@

(1.60)

-2yt\~1

Eq. (1.61) may be expressed in terms of the impedance ratio of metal and metal-air interfaces by substituting Eqs. (1.50) and

fp=e

with

added:

Round-

expression

Y (l-pam)(l—pma)(l—piae

coherent

coherently

Re-Reflections

infinite

bracket

-yt

Ip = e

+

Multiple

Round trip trip ReReflections

is

are

]

(1.62)

K-1)2 e -2ye|~1 ]

—(K"'l)

(1.63)

—— o—

Re~Reflection Correction Reflection Term (R) Absorption Term (A)

Expressing

rather

than

a

Eq.

gain,

(1.63)

and

as

a loss

converting

it

(i.e., to

shielding

decibels,

Term

effectiveness)

there

results:

K-1)2 e -2yt SEp == 20 1og10(1/rT) -= 20 1og10{} atj(1+K)2 t}”ZE""[}”(E?I) where,

Re-Reflection

Absorption

Loss,

AdB

= 8.,686at

Reflection

Loss,

RdB

= 20

Correction,

Big

= 20

(B)

loglo(l+K)2/4K

logloll-erl)z/(K+1)%e—zyt

(1.64) (1.65) (1.66) (1.67)

Eq. (1.64) is plotted in graphs in the appendices in this handbook for several metals, metal properties, metal thicknesses, distances, and frequencies, This question will now be examined in further detail of its three loss components: ( 1) absorption loss, (2) reflection loss, and (3) re-reflection loss correction.

1,18

Sec, 1.4 1.4.1

SHIELDING EFFECTIVENESS AssorpTiON Loss

Eq.

(1.65)

may

be

expanded:

AdB

where,

y = o+

or, If

metric

Eq.

and

jB8 =

since

= (1+3)

vYnfuo

B = /Yrfuc

(1.68)

is

of

units:

f in MHz,

system

AdB

and

are

(1.68) (1.69)

metals

defined

and

o,

v nfuc

(1.70)

for

= 3.3381:mils

U,

8,686t

¢ >> wme for metals

for

= 1314.3tCm where,

=

Yjeu(otjue)

= Y jwyo

a =

inch)

= 8,686at

in

(1.71) terms

t in

of

t

in mils

cm it becomes

fMqurGr

dB,

English

‘,fMqurGr

dB,

metric

permeability

and

(thousandths

for both

the

of

English

units

an

and

(1.72)

units

(1.73)

conductivity

relative

to

copper

Egs. (1.72) and (1.73) are plotted in Figs. 1.10 through 1.17 for various metals: copper, aluminum, brass, beryllium, monel, iron, stainless steel, and the exotic high-permeability metals%,

1.4,2

RerLection Loss The

reflection

tch at ite the

loss

relations

the metal-barrier impedances of Eq.

for Zy; and Eq.

(1.23)

k = A/2nr

= 1/2rrf

k =

=

2nr/A

= 1 for Combining

*

Eq.

For magnetic

(1.74)

2nrf

an

impedance

Zy _ ky/io/%

(1.74)

Z, - (1+3)/nEu/o

Yu e

far fields,

materials

upon

—

Vpoea

through

predicated

for Z,:

T

where,

are

interfaces. Thus, it is useful to su (1.49) by their equivalents from Eq.

for for

high-impedance,

low-impedance,

H

E fields fields

r > \/27 (1.77)

(u,>1),

(1.75) (1.76)

(1.77)

yields:

the

graphs

are

accurate

only

stipulated uy condition which varies with both magnetic-field (or flux density) and frequency, especially above several kHz

2.1.4).

1.19

for

the

strength (see Sec.

SHIELDING EFFECTIVENESS Sec, 1.4

L 00€ ZHROOL

ZIN00L

ZHHOL €

48ddo) 404

Aauanbaa g

Aousnbau4

ZHA0L

ZHAOL

€

*SA

ss07

%L

L =40

2100t

gt

uoriduosqy

00t

- QL

OF .

ot

a4nbi4

ZHOL

1.20

pue

0f

ot

N

© %w

ssauyoLyl

00 +

Kouonbaty

*s5507 uol3duosqy

® ut .gpv

uorydaosqy ¢5507 ‘spv Ui 8

SHIELDING EFFECTIVENESS

Sec. 1.4

ap ut “%y *ss07 uopydiosqy

wnuLwnly J404 pue

£

Aduanbaug *sA

ZHA0L

sso7

L

ZHOOL

uorlduosqy

00€

-

o€

[|°|

a4nbL4

ZHOL

1.2

ssawyoLyl

Asuanbaay

X001 Kauanbaay

>1

(1.35)

applies only depth at any

(1.97)

10g10(188.5

into

Eq.

kot),

for

(1.100)

t/§

< 0.74

and XK 2 10

(1.102) *

= 160.8 + 20 log (kcrtcm) dB, metric system

(1.105)

Eq.

(1.27)

into

Eq.

(1.101)

= 8.686t Vwfuo + 20 log10(66.6k//1rfu/0)for

-108.1 + 1314.4t_ [E k = 1 for =

Rg

* R sde

(1.103) (1.104)

yields:

SEgp _= 20 log,, («66.6 ke t/8 /RS)

To

when frequency.

= 108.9 + 20 10g10(kcrtmils) dB, English system Substituting

where,

when the frequency.

yields:

20 log, (188.5 k/R4 )

=

involving

(1.101)

become equal when 2 /§t/5 = et/(S or considered to be a corner-condition

(1.27)

(1.100)

becomes:

for t/6>>1 and K>>1

20 log10(188.5 kt/RSS)

o

(1.99)

2

compared

is

SE 45 = 20 1oglo(xet/5/4), Egqs. (1.100) t/§ = 0.74.

K/ 2t/8

20

the metal impéedances for t/§ 0.74 and K=10

+ 20 log (k//fmzurhr)

(1.107)

(1.108)

(r z A/2m)

fields

= 2nr/% for H fields = surface resistivity Zp/ (1+3) = 1/a6

facilitate

= 1/at

i o

(1.106)

equation

surface

in ohms/sq to

use,

t/§

resistivity

1.31

=

0,74

may

be

obtained

{1.1084)

SHIELDING EFFECTIVENESS

Sec, 1.4 from

§ of

Fig.

1.5

at

any

frequency

for

is plotted in Fig, 1.19 for values of from emission-source-to-metal-barrier

the

metals

used.

Ry ranging from distance values

Eq.

(1.106)

10mQ to 30Q, k of 10™%A/27 to

100A/27 and t/§ = 0.74, The shielding effectiveness will ordinarily be greater than that shown in Fig., 1.19 because of absorption loss provided t/§ > 0.74. Note that for all values of k, Sgg is basically a

reflection loss, viz, an impedance mismatch between the wave impedance and the metal impedance. Thus, the object is to economically achieve a low metal resistance using foils, conductive paints, flame-spray metals, meshes, screens, etc. as explained in Chap. 2.

1.4,5 ion

Low-FrequENcY MAGNETIC SHIELDING EFFECTIVENESS Eq.

(1.64)

applicable

presented

for

far

the

field

overall

and

shielding

electric

and

effectiveness

magnetic

fields

expressin

the

near field for any thickness of any metal. A substantial simplification of Eq. (1.64) results at and below very-low frequency for magnetic materials when t/§, K, and 2yt 1 above

2.4,

u,,

and

this to

be

= 0.1y

several

effects

thickness, (5) metal permeability and resistivity, cluded that unless all conditions are known, it is an equivalent u, and to directly use the py values equations in Sec. 1.4 for magnetic materials.

2.5

with

effect

permeability,

ing eddy current losses which are a function of (1) strength, (2) frequency, (3) distances to the metal

Fig.

in Fig.

bias,

a few hundred

kHz

take

place

includ-

magnetic-field barrier, (4) metal

Thus, it is conimpossible to define in Tab. 2.1 and the

for

an undefined

mag-

netic-field strength, whereas Fig. 2.6 shows the behavior of u, vs. magnetic~-flux density** at 60 Hz. About all one might conclude from this is that below saturation and at very low frequencies the permeability can increase up to about an order of magnitude above its rated low-

*

Magnetic-field meter.,

*%

strength

of

1 Oersted

] gauss = 10~ Tesla = 160 dBpT.

2,5

= 103/4m

= 79,58

ampere-turns/

Sec, 2.1

SHIELDING MATERIALS I

!

60 Hz

!

Hysteresis

!

= Loops © | (envelope)

g|8

1

S

1

1

I

S

-o

&

RF Shielded

&

Signal

=

T2

3

1/2

45

Field Strength in Qersteds Figure 2.3 Minor Hysteresis Loops Shown on Magnetization Curve

DC Field Strength

in Qersteds Figure 2.4 -‘Portrayal of Real World Situation

level values listed in Tab, 2.1. At and above medium frequencies (300 kHz - 3 MHz), y, > 1 for all conditions., Thus, the shielding effective~ ness curves presented in the appendices apply only for the stated values of uy used,

When the maximum magnetic-flux density may be exceeded, a double shield containing either a non-magnetic metal or a higher saturation magnetic metal should face the more hostile magnetic~field source., For hostile emissions coming from outside a box or cable shield, this means that the first layer of protective metal should face the outside, whereas if the emissions originate within, the protective metal should face the inside,

2,.1.1.2

AVAILABILITY AND APPLICATIONS

Several of the metals in Tab. 2.1 are available off-the-shelf in sheet stock form from thicknesses of about 1/64th inch (0.4 mm) or less to about 1/8th inch (3.2 mm) or more. Metals having thicknesses less

than

1/64th

inch

are

sometimes

regarded

as

foils,

Many

of

the

high-per-

meability metals come in foil thicknesses ranging from about 1 mil (25.4 um) to 10 mils (254 um). They are usually available in both sheet and tape form. The foil stock is also available in the form adhesive~backed foil in roll lengths typically up to 100 ft. (30.5

2.6

of m).

Sec, 2.1

100Hz 100k

SHIELDING MATERIALS

200 300

500

200 300

500

TkHz

2

3

2

3

10khiz

20

30

S0

100kHz

200 300

500

20

30

S0

100kHz

200 300

500

70k 50k 30k 20k 10k Tk 13 3k 2k Ik

Permeability

Relative

to Copper

700 500 300 200 100 70 50 30 20

1

100Hz

TkHz

5

10kHz Frequency

Figure

2.5

- Relative

Permeability

vs.

2.7

Frequency

1Mz

Sec. 2.1

™

SHIELDING MATERIALS

50

10k Permeability

700k

of Common

20k 30k]M

Ferromagnetic

##A110ys as a Function of Magnetic-Flux Dens

500k

700k

Measurgd ?t 60 Hertz

500K

300k

200k

200k

100k

00k

70k

70k

50k

50k

30k 20k 10k

0k

7k

7k

5k

5k

3k

3k

2k

700

700

500

500

300

300

200

50

Figure

200

Courtesy Magnetic Metals

2.6

500

Magnetic-Flux

- Relative

k

2k

Density

Permeability

vs.

2,8

3k

5k

in Gauss

7k

10k

Magnetic-Flux

20k

Density

Sec, 2.1

SHIELDING MATERIALS

The thinner non-magnetic foils, whose thickness is of the order a few mils, are widely used for R~F shielding. While there are many

stories spread around about dices clearly show that one

how mil

Reynolds Wrap saved the day, the appenof household aluminum foil can produce

shielding effectiveness to plane waves 80 dB below 1 GHz (see Sec. 2.2). Its

netic

fields,

Metal

application

however,

foils

are

involves

is

used

very in

and electric fields in excess of performance to low-frequency mag-

poor,

i.e.,

a number

of

metal-foil

of

wallpaper

is

nearly

ways.

(MFWP)

One

for

transparent.

rather

interesting

converting

an en-

tire room into a limited shielded enclosure. It exhibits considerably less shielding effectiveness than purchased shielded rooms, but also at a much lower cost. These materials have been used on occasion to construct shielded chambers of thousands of square feet (hundreds of square meters) in surface area down to small equipment enclosures. MFWP must be used in conjunction with other materials such as pressure-sensitive metal-foil tape, conductive adhesives, or conductive epoxy or caulking compounds, They also require taking a number of measures to reinstate lost shielding integrity at doors, windows and the like, MFWP usually comes in thicknesses of two to three mils (51 to 76 microns) and is made of either aluminum or copper foil or special stainless steel foil of relatively high conductivity and high permeability.

Representative shielding effectiveness is 25-40 dB for magnetic fields at 200 kHz, 80-100 dB for electric fields from 200 kHz to 10 MHz, and 60-80 dB for plane waves above 400 MHz (see Sec. 2.2) when measured in accordance with MIL-STD-285 (see Sec. 2.3).

Sometimes thin foils of the order of one mil are bonded to (metalized on) a plastic base such as 5-10 mil mylar. They can then be used as an air-inflatable structure which performs as a shielded enclosure. Such applications are discussed in Sec, 3.1.3 of Vol. 2 of the EMI/EMC Handbook Series. the

Some

basic

of

the magnetic

stock

Magnetic

supplied

Shield

Perfection

Mica

sheet

to

the

Division Company

740 Thomas Drive Bensenville, I11l. 60106 Phone: (312) 766-7800 TWX: (910) 256-4815

AD-VANCE Magnetics, Inc. 226 East 7th Street Rochester, Indiana 46975 Phone:

(219)

223-3158

metal

and/or

EMI/EMC

The

P.0.

and

foil

manufacturers

related

communities

Inter-Technical Box

23

Irvington, New Phone: (914) TWX: (710)

Group,

York 10533 591-8822 564-0802

Eagle Magnetic Company, Inc. P,0. Box 24283 Indianapolis, Indiana 46224 Phone:

2.9

(317)

297-1030

who

make

include:

Inc.

SEC, 2.1

SHIELDING MATERIALS

Micrite Company 21531 Strathern Street Carwoga Park, Calif. 91304

Phone:

2.1.2

(213)

James Millen Mfg. Co., 150 Exchange Street Malden, Mass., 02148

348-1610

Phone:

(617)

Inc.

324-4108

Pseupo-Homoceneous METALS

Metals which lack homogeneity but which do not intentionally have holes, slits, or other apertures, whether small or large, are called pseudo-homogeneous metals (PHM) in this handbook. Examples of PHM in~ clude conductive paints and coatings and the flame~spray process of metalizing an insulator. PHM may have thin areas, because lack of adequate quality control of the very process, per se, does not lend itself to homogeneity. Consequently, PHM may result in theoretical shielding effectiveness which may compare anywhere from good to poor with respect to measured results. The electrical properties of pseudo-homogeneous, conductive coatings are usually measured in units of either surface resistance per unit thickness, or in units of volume resistivity, absolute conductiv~ ity, or occasionally conductivity relative to copper. The surface resistance, Ry, is measured in chms/sq.* and is related to volume resig-

tivity,**

p:

Roge ™ IOODQ_m /tcm =

where,

39370p9—m/tmils

t = thickness

of

surface

The volume resistivity resistance in the following Gmhos/m

= %/bg.m

chms,

metric

ohms,

English

coating

is related to conductivity, manner at DC (1.1084):

= log/dectCm

Finally, the

x 107

conductivity

ohms/sq.

mhos/m)

section

*

The

having

%%

The

author

m.

Thus,

ture

term

between

is:

metric

equal

has

those

he has

refers

to

dimensions

observed

reporting

arbitrarily

to

the

on

a more

copper

D-C

each

or

selected

2,10

resistance

side.

less

resistivity

(U

the

in

equal

units

MKS

2.2)

units o,

and

surface

system

English

relative

(2.1)

system

in indicated

= 3937Q/ dectmils

5.8

system

(2.3)

system

for

copper

of

system

= 1;

a square

split of

(2.4)

in

the

ohms-cm

of

=

cross litera-

and

ohms-m.

Ocu

ohms-

Sec, 2.1

SHIELDING MATERIALS O == Onetal/%cu =

1.72

=

1.72

x 10

x 10

-6

-8

/b9~m

(2.5) :

/Rstcm’

= 6.79 x 107%/R -4

metric

e ..,

system

English

(2.6)

system

(2.7)

Eqs. (2.1) and (2.2) are plotted in Fig. 2.7 to yield surface resistance vs volume resistivity with metalized coating thickness as a parameter, Eqs. (2.6) and (2.7) are plotted in Fig.2,8 to present coating conductivity as a parameter.

relative to This figure

many

of

oping

an equivalent

expressions

2.1.2,.1

copper vs surface resistance with thickness is especially useful since it allows devel-

relative

conductivity,

shielding

effectiveness

oy,

which

throughout

can be used this

in

handbook.

the

ConpucTive PaInTs

Conductive

Emerson

and

paints

Cuming

(also

(E&C),

called

Technical

conductive

Wire

coatings)

Products

are

(Tecknit),

made

by

Acheson

Colloids, and others (see references), They are usually a lacquer, elastomeric, silicone resin, vinyl, acrylic, or latex base and require careful surface preparation. Some conductive paints require an overcoat for protection, To assure good electrical and mechanical reliability, surface preparation of plastics, woods, ceramics, and other base materials requires removing all greases, waxes, oils, dirt, mold

releases

and

foreign

matter

until

Most conductive paints may be processes: dipping, spraying, Several conductive paints are

tive

Silver

silver

a single

lacquer

paint

particulate

spray

coat

and

on

is adequate to produce 1 wil (25.4 uym) coating tivity of 0.04 ohm-m (¢ 2.8). Oven curing, if The

highly

ticularly

to

silver~filled

conductive

flexing

useful or

and

where

a

the

surface

is water-break

free.

applied by one or more of the following silk screening, roll coating, or brushing. also available in aerosol spray cans.

(e.g.,

E&C

organic

a reasonably

Eccocoat

resin

CC-2)

is

a highly

formulation.

non-porous

conduc-

In most

surface

using

cases,

air

drying

a surface resistivity of about 0.1Q/sq. for a thickness. This corresponds to a volume resis= 25 mhos/m, or o, = 0.0042; see Figs. 2.7 and possible, gives improved conductivity, elastomeric film

the

stretching.

will

(e.g.,

stretch

substrate

Air

drying

E&C

over

to which

Eccocoat

typically

100%.

it

is

CC-4)

is

Thus,

applied

results

in

it

is

also

is

par-

subject

a surface

resistance of about 50 mQ/sq. for a 1-mil coating thickness. This corresponds to a g, = 0.014, Oven curing results in a surface resistance of about 1 m/sq. or a o, = 0.68. It provides a resistance to salt

spray and has (121°C).

ing

The

an operating

Extended

use

silver-base,

exhibits

both

high

at

temperature

range of -65°F

temperatures

silicone

(e.g.,

conductivity

of E&C

and

2.1

250°

is

Eccocoat

high

(~54°C)

excellent. CC-10)

operational

to 250°F

surface

coat-

temperature

SHIELDING MATERIALS Sec. 2.1

w

1o

20° £0° -

o o

ot

£

S9SSAUNDLYL

oL

oL

|RIBW

-

L

L

{

v

‘UD-SWYQ

SWNLOA

£0°

£0”

ul A} IALISLSIY

SNOLUBA JOj AILALISLS3Y

£

€

= O

_oixe

_otxg

-

ot

ot

°"SA 43ddo) 40 adue)sysay BWN|OA

Lo*

Lo

otxe

doeung

ot

- /°2

aunbi4

2,12

d

= ops

BoRLINS

ul ddueysLSaY

aaenbg/suy)

Y

BDRJING = UL IDURISLSAY adenbg/Swy)

SHIELDING MATERIALS

Sec, 2.1

< n..a

wso_.

. otxz x

o

o0ix¢

0LXS

.oo_. € B

27

8


(2.13)

A/27)

are

with

plotted

the

in

further

Fig.

restriction

2.14,

The

figure

that for plane waves the shielding effectiveness of screen be~ relatively small above a few GHz whereas it is very significant 1 MHz. The shielding effectiveness to electric fields (R

100 mils

cm

and

line

(2540

ym)

and W/A

indicates:

2,30

G

IETIO| e

for Use

table

are

for

>>

ry

= 3 m

22.5

oz/

G-I IO

This

2.19

lines

R

Line Selection

in Fig.

graph

R

2.3.

The

R

aluminum

WOl

listings in Tab. in the figure.

- Applicable

2R

10dB 15 20 25 30 35 40 45 50 55 60 65 70

for

parameters,

lem{1.8cm|3.2cm|5.6cm{10cm{18cm|32cm|56cm|{1lm{1.8m|3.2m|5.6m

WO

SErm dB

2.3

plotted

as

oot

Table

(2.23)

s

accordance with the the applicable line

4B

are

rp

(2.22)

IR IO

and

is

RG]

(2.20)

SE4p

loss

cgligible)

2RI

and

with

(absorption

WO

> 10

o

5

SEdB

/E

milViHz T

e

(3)

(2.19)

.

(2.21)

O

>t

field)

o

5000

the near

| E

(2)

(in

G

quency

< A/2n

WO

Eqs.

r

ZI IR

)

WOk

where,

SHIELDING DENSITY

Sec, 2.2

347720 U} JGIIN WUy

THXOOE

§e

002

002

wooL

oL

oL

0§

0§

ot

0E

02

02

sl mpoL

St om0t

L

L

0§

g

2

Z2

Aouanbaug

£

Kouanbauy

£

Kouanbaagy

*sA

§'t

¢t

O0L

00L

Jybiapm

L

maa

pue

005

O0%

002

002

O0SL

OSL

ZHOOL

ZHOOL

o7

OL

OS

OS

ssauNd Lyl wnuiunly

o0¢

00E

-6L°2

ZHOE

05

*614

2,31

wnuniy

SLIN U} sSSPy

Sec, 2.2

SHIELDING DENSITY

(2)

(475

3 m distance;

t = 6.8 mils

grams/m?).

Thus,

aluminum

the

will

not

work

only

10

cm

the

(2.19)

more)

and

(2.20)

candidate t

in which metals:

.

T

( mll)ratio

and heavy

are

from

(or

thick

which

It remains to compare the options in the above example for metals than aluminum in order to determine if a lighter metal can be with the same shielding effectiveness. The answer is obtained two

too

sources

other found

Eqs.

be

magnetic

since

by using

would

for

away

applications.

shield

(175 um) and W/A = 1.55 oz/ft2

the

ratio

Egs.

(2.24)

using

the

and

(2,25)

information

are

in

=

computed

for

Tab.

2.2,

of

tpy;

is

formed

(2.24)

OrZ

(W/A/mil)2 (W/A)ratio

for weight-sensitive

Url

-m;—&;—;

Tab.

2.4

(2.25)

relative

to

copper

by

Table 2.4 - Relative Thicknesses and Weights of Some Metals for Yielding the Same Shielding Effectiveness (see Constraints) Metal

(tmil)ratio

Copper Monel Brass Steel $3 Netic Titanium Aluminum Magnesium

netic which

The above table shield as long the absorption

do not tially

W/A/mil) yatio

1 24.4 2.13 50 5.81 27.8 1.59 2.63

1 0.989 0.953 0.877 0.868 0.507 0.304 0.193

(W/8) ratrio 1 24.1 2.03 43.9 5.05 14.1 0.483 0.509

shows that steel is a very poor low-frequency magas it is operated under t/§ 10),

Eq.

under

(1.64)

which

becomes:

the

reflection

= 20 log10(0.707Kt/6) SE,.

where,

K =

dB

zw/znl=

= 20 log

(et/SK/4)

k x constant

k = A/2nr

When

10

for

=1

for

or

(1.101)

for

significant

t/é1

(1.101)

E-fields

for H-fields

(1.100)

for

is

(see Eq.(1.74)

= 27r/A

Eq.

loss

plane

is

waves

applied

for MIL-STD-285

for

any

two distances an error is developed which is a function of k alone. Thus, for any measurement distance, ry, and any user applied distance of ry, the correction in shielding efficiency, ASE4p, becomes:

ASE.

in which

it

is

= 20 1og10(rm/ru)

for E-fields

(2.26)

= 20 1og10(ru/rm)

for H-fields

(2.27)

=0

for

(2.28)

understood

that

both

rj and

2,3

plane

r,; are

waves in

the near

field.

MIL-STD-285

Sec, 2.3 When one of the distances is the far field, Eqs: (2.26) and

in

ASEgp

= 20

loglo(Zflrm/A)

in the (2.27)

for

E-fields,

r, in = 20

loglO(A/ZWru)

for

i

loglO(anu/A)

in

[

20 log,, G/Zwrm)

(2.26)

of

through rp

I1lustrative

(2.32)

= 0.305

Example

m(12

are

and

in near

other

is

and (2.29)

r, in near

and (2.30)

and

t,

in near

and

field

far

plotted

inches)

the

field

far

in

r

and

for H-fields, r,

distance

far

in

and

field

for H-fields, r

Egs.

far

and

E~fields,

r

20

near field become:

(2.31)

and r_ in near and

fields

in

Fig.

any

(2.32)

2.20

user

for MIL-STD-285

distance,

r,,

as

shown.

2.5

A manufacturer's literature states that per MIL-STD-285 a metalized silicone elastomer offers at least 90 dB of shielding effectiveness to

E-fields

at

10 MHz,

30 dB

shielding

effectiveness

and 70 dB to plane waves above VHF, Determine fectiveness at a distance of 10 meters,

and

=

67

to H-fields

the

likely

at

10 MHz

shielding

From Fig. 2.20, the correction to E fields at ry = 10 m is -23 dB to H fields is + 23 dB, Thus, for a 10 m distance SEjp (E~field) dB

and

SEgg

(H~field)

= 53

dB.

Note

that

the

10

m distance

is

the far field (ry>\/2m) at 10 MHz, since the ry = 10 m line in Fig. ends at 4.8 MHz (ry = A/27). Thus, there is no correction for SEgp (plane waves) = 70 dB.

I1lustrative

Example

The shielding effectiveness of aluminum was measured at

this

foil

50

dB

(see at

curve

a 5

cm

M,

Fig.

distance

2.19)., from

to H-fields of a 1 m distance a

What

2.20

Since both conditions are in the 20 logyp(5cm/100cm) = -26 dB. dB 24 dB. ]

2,3

two mils (51 um) sheet at 42 kHz and found to

protection

hostile

ASEg4p

26

in

2.6

foil

be

ef-

magnetic

near field, Thus, SEgp

would

be

field?

offered

Eq. (2.27) applies, (H-field) = 50 dB -

by

MIL-STD-285 Sec. 2.3

30URYSLQ 0g-

02-

48Y0Uuy £ 00¢

03 SI|NSBY 0€

G8Z-0L1S-TIW

00¢

0t

404 A{UD PLLRA UOLIIBUU0)

o1 2 %s pray-3 pazoauaoy apoL < Ps praty-3 pazaauaooun (1)

1300 dB for the iron and 88 dB for the mumetal.

3.6

3.3

HP-65 PROGRAM FOR SHIELDING EFFECTIVENESS

Most of the graphs presented in this handbook were developed by programming pertinent mathematical models on the Hewlett-Packard Model

HP-65 programmable calculator, to transfer up to 100 steps of

This calculator stored program.

selected

capacity

four working

registers

since

it

ing relations and $700 as of 1975.

has

it

(the

is

Specifically, the (1.64) is the main

Eq.

program

are

given

stack)

adequate

readily

shielding program.

in Eqs.

(1.68),

and

nine

available

to

uses a magnetic card The HP-65 contains

storage

run

off

in USA

at

to

to key

a permanent

3,3.1

in the

100-step

magnetic

(1.71),

program

card.

registers

as

(1.74)

and

frequency

o,

conductivity

relative

to

o

permeability

relative

to air

of Tab.

3.4

(1.77).

and

about

It

transfer

Register

in MHz

thin

metal

R

source-to~shield

in the

took

memory

thickness

|#1 = E~fields

#2 = H-fields

in mils distance

copper

#2 #3

(1 mil=25,4

micrometer)

#4

in meters

#5

or plane waves

6

or plane waves

label "A", in dB,

The HP-65

If it is desired to see a new shielding effectiveness input data, it is not necessary to key in registers #1 over again, It is only necessary to input one or more

on one or more

new

Stor

#1

To see the shielding effectiveness, key user takes about 10 seconds to compute the answer

based

of

relatioms into a 100This program is to the HP-65 need

Explanation

fMHz

new all

a cost

shield-

are listed below. From the magnetic the HP-65 with this Shielding Effecin the pertinent input data and store

follows:

Key In

1 or 2

It was

the

User ProcraM INSTRUCTIONS

The User Program Instructions card developed from Tab, 3.4, load tiveness Program #1513, Next, key in

of

effectiveness relation presented The supporting relations used in

quite a bit of program manipulation to get all the step program to meet the limitations of the HP-65., presented in Table 3.4, Thus, those having access

merely

registers.

many

data

and

then

3.7

key

label

"A"

again.

based on through 6 registers

Sec. 3.3

HP-65 PrOGRAM FOR SHIELDING EFFECTIVENESS

Table

3.4

- HP-65

Shielding

Card #1513Program.

0

KEYS

CODE

LBL

23

g RAD

35 42

A

KEYS

CODE

7

07

X

1 E RCL 6

01 15 3406

gx=y

3523

1

RCL 7 | E

3407 15

RCL

3407

7

X

CHS STO 7

42 3307

1 =

01 51 3z

f

RCL 7

60

71

71

vx

20

£1 LN

32 07

X

71

LBL

23

8x$Y

3507

EEX

43

RCL 1 | s

RCL 3 +

£ V< X

STO

8

RCL 4 . 7

£-1

06

3401 81

70

3403

32

vx

R+p 4 3

3308

RCL

3404 83 07

40

£l

09

70

31

01 04 81

8

3408

% RCL 7 2 40

Notes: .

61

£

31 09 71

X STO 4

o1 61

+

81

23 12 03

3408

1 +

30

LBL B 3

o1

RCL 8

71 3402

00 71

32

R+p

81 3407 02

80

80

Registers:

Rl Frequency

¢ in mils

R7

working

R2 o,

RS Ry in meters

R8

vorking

R3

R6EorH

R9

Hr

in Miz

Ré

1or?2

3.8

31

0 X

4

60 100

71

02

9

80

42

2

09

42 3407

6

90

3407

CHS RCL 7

X RCL 2

50

R/S

3 0-2 15

£

3408

ij E

32 07

CHS

08

RCL 8

01

£ LN

71

11

X

3524

81

LOG

S

gx>y

+

09

3405 1307 o1

CODE

32

RCL 5 $TO 7 1

KEYS

Ags

£

50

80

3?23

“;" 3

10

40

3401 3402

3401 81

Steps

RCL 1 | ReL 2 | X

81

Program

SHIELDING EFFECTIVENESS

RCL 1 3

30

40

gg

3

20

Title;__

11

g

10

0

Effectiveness

50

84

09

04

71 3304

100

Sec, 3.3

ILLUSTRATIVE EXAMPLES

3.3.2

IUusTRATIVE ExampPLES

The following examples will serve to illustrate the use of the HP-65 shielding effectiveness program, The results may be compared with those in the appendices* or in Sec. 3.2,

ExamE]e

#1

A sheet of 1/16 inch (i.e., 62,5 mils) iron is being considered to shield a box from a strong magnetic field originating from a 60-Hz generator located 5 feet (1.52 meters) away. Compute the shielding effectiveness in dB, After

loading

the

magnetic

for

iron

program

card

key in fyp, = 60 x 107% MHz = 60 EEX 6 CHS (8T0

2),

uy

=

1000

meters (STO 5), ness, key label

Example

and "A"

(STO

3),

t =

2 for H-field (STO and see 24 dB,

6).

into

the

HP-65

(STO 1), o, = .17

62,5

To

mils

(STO

see

4),

shielding

calculator,

for iron

Ry

= 1.52

effective~

#2

A piece of sensitive electronic equipment is located near (100 m) an A-M broadcast station antenna transmitting at 1250 kHz. Determine the shielding effectiveness of a 1/32 inch (31.25 mils) sheet metal aluminum box enclosure to E-fields or plane waves, as applicable,

(sT0

4),

see

After loading the magnetic program 1), 0, = .61 for aluminum (STO 2),

By

= 100m

(§TO

shielding

5),

and

effectiveness,

196 dB would never be required into and out

1

for

key

E-field

label

card, key in fyy, = 1.25 MHz uy = 1 (STO 3), t = 31.25 (STO or

"A"

plane-wave

Example A netic band. source ment, 300 dB

see

wave

196

(STO

dB.

6).

Note

To

that

obtained in practice because of the penetrations of the box (see Chap. 11, Vol. 3 EMC Handbook

Series). Also note that the near/far-field at 38,2 m. Thus, the box is located in the and

plane

and

conditions

apply

rather

than

interface far field

E-field

(Ry = A/27m) exists of the transmittex

conditions.

#3 ground-level nuclear detonation produces a broadband electromagpulse (EMP) with most of its energy distributed in the 10 kHz From a distance of 5 km, the blast center looks like a magnetic having billions of amperes. To protect electromagnetic equipspecify the thickness of both aluminum and sheet steel to provide isolation.

Key fygy = .01 Miz (STO 1), o, = .61 (STO 2), uy = 1 (STO 3), t *

1If you

other

like

HP-65

this

EMC

program,

programs,

contact

3.9

Don

White

Consultants,

Inc.

for

Sec, 3.3 (this

HP-65 SHIELDING EFFECTIVENESS

is

2 (STO 6).

a

guess)

= 250

Key "A"

mils

(STO

4),

R,

to see SEgg = 191 dB,

=

5000

Since

m

(STO

try t = 1 inch (1000 mils - STO 4), and again key Again try t = 800 mils (STO 4) and key "A" to see mils, it is seen that SEgp = 308 dB,. For (this is Next try

and

H/PW

=

is inadequate,

"A" 334

to see 387 dB. dB, For t = 700

the sheet steel, key op = .17 (STO 2), u, = 1000 (STO 3) and a guess) = 100 mils (STO 4). Key "A" to see SEgg = 526 dB. t = 1/16 inch (62,5 mils) to see SEyz = 362 dB, For t = 50

mils, the aluminum,

Examg1e

5),

this

shielding

effectiveness

is

308

dB,

the

same

as

700

mils

t

of

#4

A nearby

(500

m)

L-Band

weather

radar

operating

at

1300 MHz

creates

an electric-field strength of 100 V/m in an internal room in a build~ ing where a computer is to be located, It is known that the computer, its peripherals, and all interconnecting cables will not be susceptible

to

radiation

shield

for

The

below

the

3 V/m,

computer

required

Thus,

room.

shielding

determine

effectiveness

a relatively

inexpensive

is

the

ratio

of

ceiling,

and

flooring

the

field strengths or 100/3 which equals about 31 ing effectiveness of 1 mil (25.4 um) household

dB, Consider aluminum foil

lined

Key

possible

solution,

with

Here

overlapping

the walls,

joints

taped

(STO 1), oy = .61 (8TO 2), uy =1 m (STO 5), and E/PW = 1 (STO 6). the

to

the

aluminum

insure mode

provides

that

of

EMI

door

an

seams,

entry.

enormous

power

in

place.

fyy,

(STO 3), t = 1 mil Key "A" to see SEqg shielding

entrance,

3.10

the

would 1300

be

MHz

so

(STO 4), Ry = 500 = 169 dB, Thus,

effectiveness

and

=

electric-

the shieldas one

like

and

do not

it

remains

create

CHAPTER 4 REFERENCES (1

Abramowitz,

tions", (2) ing

Boulder,

Stegun,

I.A.,

Compatibility; AF/BSD Minuteman

(4)

Chicago,

1964,

Albin,

tronic

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4,12

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