Manufacturer of EMI/RFI Gasketing and Shielding Products · Electromagnetic Interference, (EMI)...
Transcript of Manufacturer of EMI/RFI Gasketing and Shielding Products · Electromagnetic Interference, (EMI)...
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
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
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
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
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
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
The Electromagnetic Wave
H-Field (magnetic) E - Field (electric) PW - Field (plane wave)
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
Half-Wavelength Sized Emission
Equipotential Bands
Radiated Field, No Shielding
Antenna Pattern Lobes
Full-Wavelength Sized emission
Typical Cross-Talk Problem
Digital Control Section
Sensitive Analog Section
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
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
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
) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) )
( ( ( ( ( ( ( (
( ( ( ( ( ( ( (
( ( (
) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) )
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
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)
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.
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
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
Holes (apertures) within a shielded enclosure
Radiated Field, Aperture in Shield
hole or slot
Leakage
PCB Trace
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
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.
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.)
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
Aperture Attenuation Modeling Program
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
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
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
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)
Honeycomb Ventilation Panels
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
Attenuation of Shielding Panels
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
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
MAJR Products Corporation MAJR Products Corporation Manufacturer of EMI/RFI GasketingManufacturer of EMI/RFI Gasketingand Shielding materialsand Shielding materials
www.majr.comwww.majr.com
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