Manufacturer of EMI/RFI Gasketing and Shielding Products · Electromagnetic Interference, (EMI)...

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Presented by Michael J. Oliver Vice President Electrical / EMC Engineering MAJR Products Corporation MAJR Products Corporation Manufacturer of EMI/RFI Gasketing Manufacturer of EMI/RFI Gasketing and Shielding Products and Shielding Products

Transcript of Manufacturer of EMI/RFI Gasketing and Shielding Products · Electromagnetic Interference, (EMI)...

Page 1: Manufacturer of EMI/RFI Gasketing and Shielding Products · Electromagnetic Interference, (EMI) •The undesirable effect due to an electrical signal other than the desired signal

Presented byMichael J. OliverVice President Electrical / EMC Engineering

MAJR Products Corporation MAJR Products Corporation Manufacturer of EMI/RFI GasketingManufacturer of EMI/RFI Gasketingand Shielding Productsand Shielding Products

Page 2: Manufacturer of EMI/RFI Gasketing and Shielding Products · Electromagnetic Interference, (EMI) •The undesirable effect due to an electrical signal other than the desired signal

Definitions

Electromagnetic Interference, (EMI)

• The undesirable effect due to an electrical signal other than the desired signal

Electromagnetic Compatibility, (EMC)

• The ability to operate in an intended environment without being disturbed or disturbing other equipment

Radio Frequency Interference, (RFI)

• Interference to communication/radio bands

Emissions• Energy generated by an

electrical device’s operation

Conducted - Transmitted by a conductive medium Radiated - Transmitted by an electromagnetic field

Immunity• A measure of how resistant an

electrical device is to external fields

Susceptibility• A measure of how susceptible a

device is to external fields

EMC Fundamentals

Page 3: Manufacturer of EMI/RFI Gasketing and Shielding Products · Electromagnetic Interference, (EMI) •The undesirable effect due to an electrical signal other than the desired signal

To have an EMI problem, three elements are necessary:

• Source

• Coupling path

• Receptor

The amount of emission “leakage”from an aperture depends upon three main items:

• The maximum linear dimension (not area) of the aperture

• The wave impedance

• The frequency of the source

Multiple AperturesReduction of shielding depends upon:

• The spacing between the apertures

• Operating frequency• The number of apertures

within /2

When apertures of equal size are placed close together (within /2), the shielding loss is approximately proportional to 20 times the log of the number of apertures.

EMC Fundamentals

Page 4: Manufacturer of EMI/RFI Gasketing and Shielding Products · Electromagnetic Interference, (EMI) •The undesirable effect due to an electrical signal other than the desired signal

EMC Fundamentals

Sources Coupling Path Receptor

Microprocessors Radiated EM fields Other logic circuitsVideo drivers Capacitance Analog circuitsESD Inductance ReceiversPower supplies Conducted Reset linesLightning “Ground” Equipment

To have an EMI problem, three elements are necessary:

• Source

• Coupling path

• Receptor

Page 5: Manufacturer of EMI/RFI Gasketing and Shielding Products · Electromagnetic Interference, (EMI) •The undesirable effect due to an electrical signal other than the desired signal

Forms the building blocks of understanding electromagnetic theory by defining the relationship among charges, currents, magnetic and electric fields.

• Gauss’s Law - There are + and - electric charges (flux) out of a surface proportional to the charge within the surface

• Faraday’s Law - Any change in the magnetic environment of a

coil will cause a voltage (emf) to be "induced" in the coil.• Ampere’s Law - A current flow creates a magnetic field.

They are functions of three space variables (x,y,z) and time (t).

They relate time-varying electric and magnetic fields to current and voltage.

MAXWELL EQUATIONS

EMC Fundamentals

http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.htmlC. R. Nave

Page 6: Manufacturer of EMI/RFI Gasketing and Shielding Products · Electromagnetic Interference, (EMI) •The undesirable effect due to an electrical signal other than the desired signal

A time varying electric field between two conductors represented as a capacitor.

A time varying magnetic field between two conductors represented by mutual inductance.

A potential difference causes a current to flow which generates a magnetic field which, in turn, creates an electric field.For a time-varying field, we always have both an electric field and a magnetic field.

An RF voltage potential will cause a time varying current –generating magnetic field, developing a time varying transverse electric field, creating the electromagnetic field.

EMC Fundamentals

MAXWELL EQUATIONS

Page 7: Manufacturer of EMI/RFI Gasketing and Shielding Products · Electromagnetic Interference, (EMI) •The undesirable effect due to an electrical signal other than the desired signal

The Electromagnetic Wave

H-Field (magnetic) E - Field (electric) PW - Field (plane wave)

Page 8: Manufacturer of EMI/RFI Gasketing and Shielding Products · Electromagnetic Interference, (EMI) •The undesirable effect due to an electrical signal other than the desired signal

EF, HF, & Plane Wave

The Electric Field (high impedance), Magnetic Field (low impedance), and Plane Wave (377 Ohm) are the three aspects of EMI/RFI wave propagation. Different shielding levels result from variations in wave impedance.

Electric Field and Magnetic Field impedance change with separation distance.

Plane Wave impedance is constant with separation distance.

High-Z

Low-Z

377 Ohm

Page 9: Manufacturer of EMI/RFI Gasketing and Shielding Products · Electromagnetic Interference, (EMI) •The undesirable effect due to an electrical signal other than the desired signal

Half-Wavelength Sized Emission

Equipotential Bands

Radiated Field, No Shielding

Antenna Pattern Lobes

Full-Wavelength Sized emission

Page 10: Manufacturer of EMI/RFI Gasketing and Shielding Products · Electromagnetic Interference, (EMI) •The undesirable effect due to an electrical signal other than the desired signal

Typical Cross-Talk Problem

Digital Control Section

Sensitive Analog Section

Page 11: Manufacturer of EMI/RFI Gasketing and Shielding Products · Electromagnetic Interference, (EMI) •The undesirable effect due to an electrical signal other than the desired signal

Board Level Shielding

Digital Control Section

Sensitive Analog Section

P.C. Board grounding layer

Metal shield soldered to P.C.B.

Rayleigh-Helmholtz & Carson reciprocity theorem:

Resolving radiated emission problems will also aid in resolvingradiated immunity problems

Page 12: Manufacturer of EMI/RFI Gasketing and Shielding Products · Electromagnetic Interference, (EMI) •The undesirable effect due to an electrical signal other than the desired signal

Reciprocity -Emission and Immunity

Reciprocity

Rayleigh-Helmholtz & Carson reciprocity theoremSame frequencyMedium is linear, passive, and isotropic

If a signal is applied and transmitted through antenna A and measured at another antenna B; an equal signal will be measured at antenna A if the same signal is transmitted through antenna B

Basically means that resolving radiated emission problems will also aid in resolving radiated immunity problems

Page 13: Manufacturer of EMI/RFI Gasketing and Shielding Products · Electromagnetic Interference, (EMI) •The undesirable effect due to an electrical signal other than the desired signal

The Problem with a Partial Shield

Improvement on the shielded side.

Constructive interference makes signal stronger on this side.

Radiated field with no shielding.

Radiated field with shielding on one side.

Reflections

PCB Trace

Page 14: Manufacturer of EMI/RFI Gasketing and Shielding Products · Electromagnetic Interference, (EMI) •The undesirable effect due to an electrical signal other than the desired signal

) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) )

( ( ( ( ( ( ( (

( ( ( ( ( ( ( (

( ( (

) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) )

P1

A

B

R

P2

Shielding Material (Graphical Representation)

Note: If A 6 dB then B=0

Incident Wave

Attenuated Wave

1 st Internal Reflected Wave

2 nd Internal Reflected Wave

ABSORPTION:A (dB) = 3.338 t (µr r F)^1/2

PLANE WAVE REFLECTION:RP (dB) = 108.1 - 10 Log (µr F/ r)

WHERE:t = Thickness in milsµr = Relative permeability

r = Relative conductivityF = Frequency (MHz)

t

Page 15: Manufacturer of EMI/RFI Gasketing and Shielding Products · Electromagnetic Interference, (EMI) •The undesirable effect due to an electrical signal other than the desired signal

R.F. Current flowing through a conductor is non-uniform.

Current density is highest at the surface, and becomes exponentially smaller with depth into the conductor.

The parameter quantifying this occurrence is called ‘Skin Depth’ ( ).

Incident Wave

1 Skin Depth

1 Skin Depth

1 Skin Depth

Reflection

Surface Currents (Good Shield)

Absorption (dB)where : RdB = Reflection losses

AdB = Absorption losses

BdB = Re-reflection losses

SE(dB) = 10 log P1 / P2

= SE(dB) + R(dB) + A (dB) + B(dB)

Internal Reflected Wave (B)

Page 16: Manufacturer of EMI/RFI Gasketing and Shielding Products · Electromagnetic Interference, (EMI) •The undesirable effect due to an electrical signal other than the desired signal

fair) torelative material (ofty Permeabili

(Siemens)ty Conductivi

(Hz)Frequency f

where:

Definition of Skin Depth

Skin effect increases as frequency and amplitude of the losses increase therefore at higher harmonic frequencies there is a greater degree of heating in a conductor.

Each skin depth equals approx 37% of the amplitude of the propagating wave through the material.

Page 17: Manufacturer of EMI/RFI Gasketing and Shielding Products · Electromagnetic Interference, (EMI) •The undesirable effect due to an electrical signal other than the desired signal

Skin Depth v.s. Frequency For Common Shielding Materials

Holes Dominate

Material Dominates

Smaller is Better

Frequency (Hz)10 100 1000 1k 10k 100k 1M 10M 100M 1G 10G 100G

Skin

Dep

th (

mm

)

0

1

2

3

4

5

6

7

8

9

10

CopperMild Steel Aluminum Stainless Steel

Page 18: Manufacturer of EMI/RFI Gasketing and Shielding Products · Electromagnetic Interference, (EMI) •The undesirable effect due to an electrical signal other than the desired signal

Magnetic Alloys CRT’s, Coils, Transformers

Mild Steel Computers, Telecom Racks

Aluminum BeCu

Avionics, Portable Equipment Shielding gaskets

Stainless Steel Snap-In Covers, Grounding Strips

Flame Spray Coatings Plastic Housings

Metallic Plating Small Plastic Housings

Filled Plastics ESD Shielded Housings

Conductive Paint Architectural, Plastic Housings

Material Typical Uses

Common Shielding Materials

Page 19: Manufacturer of EMI/RFI Gasketing and Shielding Products · Electromagnetic Interference, (EMI) •The undesirable effect due to an electrical signal other than the desired signal

Holes (apertures) within a shielded enclosure

Page 20: Manufacturer of EMI/RFI Gasketing and Shielding Products · Electromagnetic Interference, (EMI) •The undesirable effect due to an electrical signal other than the desired signal

Radiated Field, Aperture in Shield

hole or slot

Leakage

PCB Trace

Page 21: Manufacturer of EMI/RFI Gasketing and Shielding Products · Electromagnetic Interference, (EMI) •The undesirable effect due to an electrical signal other than the desired signal

The amount of leakage from an aperture depends upon three main items:

The maximum linear dimension (not area) of the aperture

The wave impedance

The frequency of the source

Shield Aperture Leakage

Page 22: Manufacturer of EMI/RFI Gasketing and Shielding Products · Electromagnetic Interference, (EMI) •The undesirable effect due to an electrical signal other than the desired signal

Current Flow Around a Slot

R.F. Current Lines

Area of high current density. Impedance is higher here.

Fringing field. A fraction of the current radiates across the slot instead of going around it.

Page 23: Manufacturer of EMI/RFI Gasketing and Shielding Products · Electromagnetic Interference, (EMI) •The undesirable effect due to an electrical signal other than the desired signal

Frequency (Hz)

100k 1M 10M 100M 1G 10G 100G

Ape

rtur

e Si

ze

120 dB100 dB80 dB60 dB40 dB20 dB

1 m

1 nm10 nm

100 nm

10 m100 m

1 mm1 cm

10 cm1 m

10 m

100 m1 km

Shielding Level of an Aperture

L2log20essEffectiven Shielding 10

DimensionLongest sec/103Light of Speed

Frequency/Wavelength

8

LmC

FFC

Shielding Effectiveness

(0.059 in.)

Page 24: Manufacturer of EMI/RFI Gasketing and Shielding Products · Electromagnetic Interference, (EMI) •The undesirable effect due to an electrical signal other than the desired signal

Multiple Apertures

Reduction of shielding depends upon:the spacing between the aperturesthe frequencythe number of apertures

When apertures of equal size are placed close together (within /2), the shielding loss is approximately proportional to 20 times the log of the number of apertures.

Aperture calculations

Page 25: Manufacturer of EMI/RFI Gasketing and Shielding Products · Electromagnetic Interference, (EMI) •The undesirable effect due to an electrical signal other than the desired signal

Aperture Attenuation Modeling Program

Page 26: Manufacturer of EMI/RFI Gasketing and Shielding Products · Electromagnetic Interference, (EMI) •The undesirable effect due to an electrical signal other than the desired signal

We saw the need for a software design tool to assist engineers in the initial shielding design stage of their electronic product

A modeling program that we can input the products’ frequency of concern, aperture size, and quantity of apertures for connectors and/or heat management of the shield or enclosure

An output indicating approximate but conservative shielding levels prior to expensive radiated emission and/or susceptibility testing

A graph of aperture attenuation (dB) vs. frequency (MHz)

Aperture Attenuation Program

Page 27: Manufacturer of EMI/RFI Gasketing and Shielding Products · Electromagnetic Interference, (EMI) •The undesirable effect due to an electrical signal other than the desired signal
Page 28: Manufacturer of EMI/RFI Gasketing and Shielding Products · Electromagnetic Interference, (EMI) •The undesirable effect due to an electrical signal other than the desired signal

An important aspect of a shielding effectiveness modeling:

• To verify theoretical shielding calculation error with a radiated emission of a shielded product under test

• Analyze results

• Adjust calculations to reduce shielding error based on analysis of the actual test

• Keep in mind that even though important to reduce errors every radiated set-up is unique and incorporates its own anomalies such as reflections, resonances, coupling, VSWR losses, etc…

Modeling Fundamentals

Page 29: Manufacturer of EMI/RFI Gasketing and Shielding Products · Electromagnetic Interference, (EMI) •The undesirable effect due to an electrical signal other than the desired signal

Antenna 2, Far Field C ircuit IsolationSpecific transceiver technologies for the cellular industry

Frequency (MHz)

1500 1600 1700 1800 1900 2000 2100 2200 2300 2400 2500

Circu

it Isola

tion (d

B)

0

10

20

30

40

50

60

70

80

90

100

110

120

Dynam ic Range Leve l P in M ount P in M ount (half p ins) Surface Mount Surface Mount (half tabs) Surface Mount (corners so ldered)

Bluetooth2402 - 2480

GPS1575.42

TDM A / GSM1850 - 1990

W CDM A1920 - 2170

PCB Shield Measurement

60 dB

43 dB

Page 30: Manufacturer of EMI/RFI Gasketing and Shielding Products · Electromagnetic Interference, (EMI) •The undesirable effect due to an electrical signal other than the desired signal

Aperture Attenuation Program

• Factor of 10 =15 dB

• Factor of 5 = 8.46 dB

• Factor of 1 =1.7 dB

Aperature 40Test Factor

S h ie ld in g E ffe c tiv e n e s s G r a p h o f A p e ra tu r e E ffe c ts fo r a n E n c lo s u re o r P r in te d C irc u it B o a rd S h ie ld

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

45.00

50.00

55.00

60.00

65.00

70.00

75.00

80.00

85.00

90.00

95.00

100.00

2000 2200 2300 2400 2500 2600 2700 2800 2900 3000

F re q u e n c y (M H z )

Sh

ield

ing

Eff

ectiv

enes

s (d

B)

Page 31: Manufacturer of EMI/RFI Gasketing and Shielding Products · Electromagnetic Interference, (EMI) •The undesirable effect due to an electrical signal other than the desired signal
Page 32: Manufacturer of EMI/RFI Gasketing and Shielding Products · Electromagnetic Interference, (EMI) •The undesirable effect due to an electrical signal other than the desired signal

Honeycomb Ventilation Panels

Page 33: Manufacturer of EMI/RFI Gasketing and Shielding Products · Electromagnetic Interference, (EMI) •The undesirable effect due to an electrical signal other than the desired signal

Attenuation of Plated Honeycomb Shielding Panels

100+909035PW1 GHz

100+959040PW400 MHz

100+959030PW100 MHz

100+908060E10 MHz

80606540H1 MHz

65504020H100 kHz

60303020H10 kHz

(dB)(dB)(dB)(dB)

FieldFrequency

TinPlating

TinPlating

NickelPlating

Chromate Plating

Steel H/CAlum H/CAlum H/CAlum H/C

Shielding Effectiveness vs. plating and honeycomb materials

Page 34: Manufacturer of EMI/RFI Gasketing and Shielding Products · Electromagnetic Interference, (EMI) •The undesirable effect due to an electrical signal other than the desired signal

Attenuation of Shielding Panels

Page 35: Manufacturer of EMI/RFI Gasketing and Shielding Products · Electromagnetic Interference, (EMI) •The undesirable effect due to an electrical signal other than the desired signal

Shielding Products and Materials

MAJR Products Corporation

An internationally recognized manufacturer of Shielding Products

Offering:EMI/RFI Honeycomb Ventilation panelsShielded windowsKnitted wire mesh gasketsMulticon oriented wire gasketsConductive fabric gaskets Board Level ShieldsEMC ConsultingFingerstock gasketsConductive ElastomerDie-Cut gasketsGrounding washersThermal materialsFerrites and RF Absorber

www.majr.com

ISO-9001:2000 Registered

Page 36: Manufacturer of EMI/RFI Gasketing and Shielding Products · Electromagnetic Interference, (EMI) •The undesirable effect due to an electrical signal other than the desired signal

REFERENCES

ELECTRONIC SYSTEM DESIGN: INTERFERENCE AND NOISE CONTROL TECHNIQUESJohn R. Barnes - Englewood Cliffs, NJ: Prentice-Hall, Inc. 1987

DIGITAL DESIGN FOR INTERFERENCE SPECIFICATIONSR. Kenneth Keenan - Pinellas Park, FL: TKC, 1983

DECOUPLING AND LAYOUT OF DIGITAL PRINTED CIRCUITSR. Kenneth Keenan- Pinellas Park, TKC, FL: 1985

INTERFERENCE CONTROL IN COMPUTERS AND MICROPROCESSOR BASED EQUIPMENTMichel Mardiguian - Gainesville, VA: Interference Control Technologies, 1984

NOISE REDUCTION TECHNIQUES IN ELECTRONIC SYSTEMSHenry W. Ott - New York: John Wiley & Sons, 1976

ELECTROMAGNETIC WAVESS.A. Schelkunoff - Princeton, NJ: D. VanNostrand Co., Inc., 1943

EMC HANDBOOK VOL III EMI CONTROL METHODS AND TECHNIQUESDonald R.J. White - Gainesville, VA: don White Consultants, Inc., 1973

EMI CONTROL IN THE DESIGN OF PRINTED CIRCUIT BOARDS AND BACKPLANESDonald R.J. White - Gainesville, VA: Interference Control Technologies, 1981

ANSI/IPC-D-275: DESIGN STANDARD FOR RIGID PRINTED BOARDS AND RIGID PRINTED BOARD ASSEMBLIES, SEP 1991Institute for Interconnecting and Packaging Electronic Circuits - Lincolnwood, IL

IPC-D-316: DESIGN GUIDE FOR MICROWAVE CIRCUIT BOARDS UTILIZING SOFT SUBSTRATES, NOV 1994Institute for Interconnecting and Packaging Electronic Circuits - Lincolnwood, IL

IPC-D-317A (DRAFT); DESIGN GUIDELINES FOR ELECTRONIC PACKAGING UTILIZING HIGHSPEED TECHNIQUES, JAN 1995Institute for Interconnecting and Packaging electronic Circuits - Lincolnwood, IL

Acknowledgment for partial assembly of this presentation: Ron Brewer, Gary Fenical, Ed Nakauchi, and Bill Stickney

Page 37: Manufacturer of EMI/RFI Gasketing and Shielding Products · Electromagnetic Interference, (EMI) •The undesirable effect due to an electrical signal other than the desired signal

MAJR Products Corporation MAJR Products Corporation Manufacturer of EMI/RFI GasketingManufacturer of EMI/RFI Gasketingand Shielding materialsand Shielding materials

www.majr.comwww.majr.com

Page 38: Manufacturer of EMI/RFI Gasketing and Shielding Products · Electromagnetic Interference, (EMI) •The undesirable effect due to an electrical signal other than the desired signal

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