Introduction to Immunity and Susceptibility

Introduction to Immunity &

Susceptibility

Randy J. Jost, Ph. D.

August 3, 2014

[email protected]

MO-AM-1

Overview

• Description of Immunity & Susceptibility

• Source of unwanted signals

– Electromagnetic Environment

– RF and transient immunity issues

• Path of unwanted signals

– Conducted signals

– Radiated signals

• Victims of unwanted signals

• Mitigation Strategies

• Electrostatic discharge (ESD)

• Summary

What is Electromagnetic Compatibility?

• Electromagnetic Compatibility (EMC) is the ability

of an electronic system to

– Function properly in its intended Electromagnetic

Environment (EME)

– Not be a source of interference to other systems in

that (or any other) Electromagnetic Environment

• Based on the above, EMC has two major

components

– Susceptibility / Immunity

– Emission control

• Conducted Emissions

• Radiated Emissions

Electromagnetic Environment

What is Electromagnetic Compatibility?

Source (Transmitter) => Path => Victim (Receiver)

Immunity / Susceptibility

• Immunity is the ability of a system or device (the receiver or victim equipment) to operate correctly in the presence of electromagnetic emissions in all designed for electromagnetic environments.

• Immunity and susceptibility are opposites -equipment which has high immunity has low susceptibility, and vice versa.

• The goal of EMC design is to develop a system which has high immunity, as well as low or no emissions, except for those intended to be emitted.

• Good system design and good EMC design are two sides of the design coin.

Understanding Immunity/Susceptibility

• The easiest way to understand the concepts of

Immunity/Susceptibility is to start with the

traditional EMC model:

Source => Path => Victim

• Your guiding thought should be “follow the

electrons (or fields)”

• You must follow ALL the electrons (fields)

– Not just the ones you wanted

– Not just the ones you put there intentionally

– Not just the ones you know about

SOURCES

• There are many sources of unwanted energy

– Sources external to the system, equipment or devices (victim)

– Sources internal to the system, equipment or devices (victim)

• The totality of these electromagnetic emissions are called the Electromagnetic Environment (EME)

• The impact of the electromagnetic environment on systems, equipment or devices is called Electromagnetic Environment Effects (E3)

SOURCES

• 4.124 environment, electromagnetic.

(1) The time distribution of the levels of power,

voltage(s),current(s), and electric and magnetic field(s),

within various frequency ranges, of the conducted and

radiated electromagnetic emissions that may be

encountered in the environment of a system or

subsystem when performing its assigned mission.

(2) The totality of electromagnetic phenomena existing at a

given location. (IEC 50(161)(1990) [7]) (NATO [15])

ANSI C63.14-1992 American National Standard Dictionary for Technologies of Electromagnetic

Compatibility (EMC), Electromagnetic Pulse (EMP) , and Electrostatic Discharge (ESD)

SOURCES

• 4.102 electromagnetic environment effects (E3). The impact of the electromagnetic environment upon

the operational capability of electronic or electrical

systems, equipment, or devices. It encompasses all

electromagnetic disciplines, including electromagnetic

compatibility; electromagnetic interference;

electromagnetic vulnerability; electromagnetic pulse;

electronic countermeasures; hazards of electromagnetic

radiation to ordnance and volatile materials; and natural

phenomena effects of lightning and precipitation static

(p-static). (NATO [15])

ANSI C63.14-1992 American National Standard Dictionary for Technologies of Electromagnetic

Compatibility (EMC), Electromagnetic Pulse (EMP) , and Electrostatic Discharge (ESD)

SOURCES

• Practical definition of EME

– The measureable electromagnetic field(s) that

exist within a definable region(s) where

equipment or systems must operate, either

individually or in conjunction with other

equipment or systems

– Note that an electromagnetic environment may

be composed of several sources of

electromagnetic fields depending upon the

specific quantities measured

SOURCES

• Electromagnetic Environments can be characterized in many ways.

• One way to look at them is to subdivide them into two major location categories:

– Interior or Indoor

– Exterior or Outdoor

• In a similar fashion, noise sources can be subdivided into two major categories:

– Natural Noise Sources

– Man-made Noise Sources

• Immunity evaluation must take into account all relevant combinations of noise and location

Interior/Indoor Environment Regions

• Residential

• Industrial

• “Special” Cases (examples)

– Shielded room, anechoic

– Shielded room, non-anechoic

– Hospitals and Medical Centers

– High background situations

Environment Regions – Indoors

Source: http://www.ets-lindgren.com/page/?i=iSeries-71

Source: http://www.ets-lindgren.com/page/?i=MicrowaveChambers

Source: http://www.dundee.ac.uk/medther/tayendoweb/images/mriscnr.jpg

Exterior/Outdoor Environment Regions

• Rural

• Suburban

• Urban

• “Special” Cases (examples)

– Open Area Test Sites (OATS)

– High background situations

• High Voltage Substations and Switch Yards

• Airports, Military Bases, Aircraft Carriers

Environment Regions – Outdoors

http://www.npl.co.uk/electromagnetics/rf-microwave/products-

and-services/test-site-evaluation

http://www.teseq.com/com/en/products_solutions/systems/

chamber_calibration/chamber_calibration_reader.php

Environment Regions – Outdoors

http://205.243.100.155/frames/500_kV_Switch1.jpg

http://205.243.100.155/frames/B-1196 switching failure.JPG

Westfield Shoppingtown Office Tower at Doncaster, Victoria.

Environment Regions – Outdoors – AirportsTypical airport comm./nav. spectrum usage:

Communication

VHF: 118-137 MHz

UHF: 243-380 MHz

Marker Beacon

75 MHz

Non-Directional Beacon (NDB)

190-530 kHz

1600-1800 kHz

Instrument Landing System (ILS)

Localizer: 108.1-111.95 MHz

Glide Slope: 329.15-335.0 MHz

VHF Omnidirectional Range (VOR)

108.0-117.95 MHz

Distance Measuring Equipment (DME)

Ground: 962-1213 MHz

Air: 1025-1150 MHz

Tactical Air Navigation (TACAN)

Ground: 960-1215 MHz

Air: 1023-1152 MHz

One location can have very many frequencies to deal with

Environment Regions – Outdoors – Airports

http://www.boston.com/news/local/massachusetts/articles/2005/10/13/new_antenna_ends_radar_errors_at_logan/

Typical aviation radar spectrum usage:

L Band

Secondary Surveillance Radar – 1030-1090 MH

Long Range Surveillance Radar – 1240-1370 MHz

S Band

Primary Surveillance Radar – 2700-2900 MHz

NEXRAD WX Radar – 2700-3000 MHz

C Band

Radar Altimeter – 4200-4400 MHz

Airborne WX Radar – 5350-5470 MHz

Terminal Doppler WX Radar – 5600-5650 MHz

X Band


Surface Detection Radar – 9.0-9.2 GHz

Precision Approach Radar – 9.0-9.2 GHz


Ku Band

WX Radar – 13.25-13.4 GHz

Surface Detection Radar – 15.7-16.2 GHz

One location can have very many frequencies to deal with

The Natural Electromagnetic Environment

• The Natural Electromagnetic Environment


– Effects of Natural Noise on System Performance

• Man-made EM Noise Sources

– Noise Sources

– Effects of Man-made Noise on System Performance




• Terrestrial Sources

• Celestial Sources



– Noise Sources





• Terrestrial sources

– Lightning discharges

– Emissions from atmospheric gases

– Ground and other obstructions within the main beam of

antennas

Source: http://www.uwec.edu/jolhm/EH3/Group2/Pictures/lightning.jpg Source: http://apod.nasa.gov/apod/image/0603/aurora_andreassen_big.jpg

Source: http://apod.nasa.gov/apod/ap140420.html


Natural Noise from 0.1 Hz to 10 kHz


Natural Noise from 10 kHz to 100 MHz


Natural Noise from 100 MHz to 100 GHz





• Elevation of the noise floor

• Reduced receiver sensitivity

• In severe cases, can damage measurement systems or

the system under consideration


– Noise Sources

– Effects of Man-made Noise on System

Performance

The Man-made Electromagnetic Environment





– Noise Sources

• Unintentional Emissions of EM Energy

• Intentional Emissions of EM Energy

– Gaussian or white noise

– Impulsive noise

– Transient noise




– Noise Sources

• Many types of man-made noise/signal for many reasons

– Characterize by “Reason”

• Unintentional Emissions of EM Energy

• Intentional Emissions of EM Energy

– Characterize by Type

• System Generated Signals

• Gaussian or white noise

• Impulsive noise

• Transient noise

Transient Signals – EMP• Actual waveform dependent upon many

factors

• High-Altitude Burst EMP

• Low-Altitude Burst EMP

• Surface Burst EMP

• MHD EMP

• System Generated EMP (SGEMP)

• Internal Generated EMP (IEMP)

• Characterized as “double exponential”

waveform

• For analysis construct a generalized high-

altitude EMP electric- and magnetic-field

time waveform.

• Short rise time (High Freq. Content)

• Long fall time (Low Freq. Content)

• Large amplitude in generation

region

( ) ( ) ( )4 6 85.25 10 exp 4 10 exp 4.76 10 V

E t x x t x tm

= − − −

Typical Parameter Values

Peak value: 50 kV/m

Trise_10-90%: 5 nsec

Tfall_50%: 200 nsec

Transient Signals – EMP

High-altitude EMP spectrum and

normalized energy density spectrum

( )( ) ( )

13

6 8

2.47 10 sec

4 10 4.76 10

x VE

mj x j xω

ω ω

− =

+ +

While both lightning and EMP are

transient phenomena, they have

distinctly different responses.

Transient Signals – Lightning• Strike instantaneous currents range from 2

kA to 200 kA

• Typical strikes have 18kA – 20 kA of current

Lightning Frequency Spectrum

• According to NASA Technical

Memorandum 87788, the lightning strike

spectrum has substantial content up to 300

MHz

• Comparison of frequency spectra of a

lightning current surge (blue – according to

K Berger) and a test current surge of

10/350 µs (red – according to IEC 61312-1)






– Noise Sources

– Effects of Man-made Noise on System

Performance

• Elevation of the noise floor

• Reduced receiver sensitivity

• In severe cases, can damage measurement systems or

the system under consideration

Effect of Man-made Noise: Aircraft Carrier

Apertures

Sources

Receivers (victims)

Effect of Man-made Noise: Aircraft Carrier

USS Enterprise (CV-65)14 January 1969

Massive fire started when a Zuni rocket

accidentally exploded under the wing of an

F-4.

Losses totaled 28 dead, 343 wounded, and

15 aircraft destroyed. Required 3 months for

repairs, primarily to flight deck armor plating

USS Forrestal (CV-59)29 July 1967

Caused by the “self-firing” of a Zuni missile

134 Dead, 161 injured, 21 aircraft stricken

from inventory; Required almost 7 months

for repairs. Cost to US Navy - $72 Million

Path

• Signal/Energy Paths often considered to be

due to radiation or conduction.

• In all day-to-day situations, you will always

have both paths to deal with

– One or the other may dominate in certain regions

of the device, system or external environment

– Maximum immunity achieved when both

addressed

Propagation Path - Radiated

• Signals may be propagated over short or long distances.

• Distances should be thought of in wavelengths

• For long distance propagation (far-field), interfering signals may be attenuated (reduced) enough to be a non-issue.

• Short range propagation (near-field) is another matter

• Sufficient attenuation may only be achieved by adding appropriate absorbers or shielding.

Propagation Path - Radiated

• Far-field propagation (long distance - many λ’s)

– Fields will decrease from source as 1/r

– Need to consider multipath and blockage

• Near-field propagation (short distance - few λ’s)

– Fields contain 1/r2 & 1/r3 terms

– Certain assumptions that are used in the far field are

NOT valid in the near field

Far Field vs. Near Field

Source: Capps, C., “Near field or far field?”,EDN, pp 95-102, August 16, 2001.

(((( )))) j ro

2 2 3

kI 1 1 1 VE j sin e

4 r jkr k r m

ββββθθθθ η θη θη θη θ

ππππ−−−−

= + −= + −= + −= + −

llll

(((( )))) jkro

2

kI 1 1 AH j sin e

4 r jkr mφφφφ θθθθ

ππππ−−−−

= += += += +

llll

(((( )))) j ro

r 2

I 1 1 VE cos e

2 jkr r m

ββββη θη θη θη θππππ

−−−− = += += += +

llll

Fields from an infinitesimal dipole antenna

2 2k ω µεω µεω µεω µε====

119.9169832

120

376.730313...

µµµµηηηη

εεεε

π Ωπ Ωπ Ωπ Ω

π Ωπ Ωπ Ωπ Ω

ΩΩΩΩ

====

====

≈≈≈≈

≈≈≈≈

length of dipole

radius of dipole

( )

a ( a )

λλλλ

λλλλ

====

====

l l l l l l l l

Far Field vs. Near Field

Source: Capps, C., “Near field or far field?”,EDN, pp 95-102, August 16, 2001.

Rayleigh criterion for path difference: phase error of 1/16 of wavelength

Atmospheric Attenuation

VICTIM

• Victim is any system that has paths into it for transferring unwanted energy into the system or has operational vulnerabilities due to lack of robust design.

– Conductive Paths

• Lines through penetrations

• Existing lines in system

– Radiated (Energy) Paths

• Apertures/Holes

• Antennas – Intentional and unintentional

– Operational Vulnerabilities

• Low “margins/tolerances”

• Lack of error checking and correction

Interference – Standards

• With regards to “standards”, there are two

types to be aware of

– HOW to measure emissions, radiated or

conducted

• Example: ANSI C63.4 (American National Standard for

Methods of Measurement of Radio Noise Emissions

from Low-Voltage Electrical and Electronic Equipment

in the Range of 9 kHz to 40 GHz)

– WHAT the limits are, radiated or conducted

• Example: FCC Part 15

• Example: CISPR 22

Interference – Standards

CISPR Class A Conducted EMI Limit

Frequency of Emission

(MHz)

Conducted Limit (dBμV)

Quasi-peak Average

0.15 - 0.50 79 66

0.50 - 30.0 73 60

CISPR Class B Conducted EMI Limit


(MHz)

Conducted Limit (dBμV)

Quasi-peak Average

0.15 - 0.50 66 to 56* 56 to 46*

0.50 - 5.00 56 46

5.00 - 30.0 60 50

CISPR Class A 10-Meter Radiated EMI Limit


(MHz)Field Strength Limit (dBμV/m)

30 - 88 39

88 - 216 43.5

216 - 960 46.5

above 960 49.5

CISPR Class B 3-Meter Radiated EMI Limit


(MHz)Field Strength Limit (dBμV/m)

30 - 88 40

88 - 216 43.5

216 - 960 46.0

above 960 54.0

*Decreases with the logarithm of the frequency.

Field strength limits for conducted and radiated emissions

FCC Class A Conducted EMI Limit


(MHz)Conducted Limit (μV)

0.45 - 1.6 1000

1.6 - 30.0 3000

FCC Class B Conducted EMI Limit


(MHz)Conducted Limit (μV)

0.455 - 1.6 250

1.6 - 30.0 250

FCC Class B 3-Meter Radiated EMI Limit


(MHz)Field Strength Limit (μV/m)

30 - 88 100

88 - 216 150

216 - 1000 200

above 1000 200

FCC Class A 30-Meter Radiated EMI Limit


(MHz)Field Strength Limit (μV/m)

30 - 88 30

88 - 216 50

216 - 1000 70

above 1000 70

Interference – Conducted Signals

• Common Mode Signals

• Differential Mode Signals

• Power Lines

• Control Lines

• Signal Lines

– Analog

– Digital

Interference – Conducted Signals

• Common Mode Signals

• Differential Mode Signals

Decomposition of the currents on a two-

wire transmission line into common-mode,

IC, and differential-mode, ID, components.

I1 = IC + ID

I2 = IC – ID

ID = ½(I1 –I2)

IC = ½(I1 + I2)

Susceptibility Mitigation

• Must consider both radiated and conducted

signals

Illustration of the relative radiated emission potential of (a) differential-mode currents and

(b) common-mode currents. Notice that common-mode currents are the most likely

source of radiated electric fields. Also, a small common-mode current can produce the

same level of radiated electric field as a much larger value of differential-mode current.

Mitigation of Radiated Signals• Design Strategies

– Enclosures

– Location (Distance)• Near Field

• Far Field

• Eliminate Unwanted Antennas

• Eliminate Unneeded Apertures / Holes

• Shielding

• Filtering– RF Filters

– Chokes

• Attenuation by Materials– Absorbers

– Gaskets

Mitigation of Radiated Signals – Shielding

• Shielding Against Conducted Coupling

• Shielding Against Radiated Coupling

• Shielding Against Static/Quasi-static Electric Fields

• Shielding Against Static/Quasi-static Magnetic Fields

• See Dr. Todd Hubing’s Fundamentals presentations on Grounding and on Shielding for detailed explanations

Mitigation of Radiated Signals – Shielding

Yes, there is such a thing as too much shielding …

Mitigation of Conducted Signals

• Design Strategies

• Transient Voltage/Overvoltage Suppression

Devices (TVS/OVS)

• Filters

• Ferrites

• Line Impedance Stabilization Networks (LISN)

Impedance of AC Power Line

• Plot of minimum and

maximum impedance of the

115-V AC power line.

• Based on measurements

from 36 unfiltered

commercial AC power lines at

different locations across the

US.

• Impedance values range from

approximately 2 to 450 Ω.

• This widely varying

impedance makes consistent,

repeated conducted

emissions tests very difficult

Mitigation of Conducted Signals - LISN

• Line Impedance Stabilization Networks (LISN)

• Used when testing products (DUT) to see if they meet conducted emissions requirements

• LISNs have several purposes:

– Provides a known, stable, and reasonable impedance to the DUT from the power line over the frequency range of the conducted emission test (150 kHz – 30 MHz)

– Filters or suppresses noise from the power line so that it does not interfere with the measurement of the conducted emissions due to the DUT

– Provides a port for the measurement of the conducted emissions from the product

– Provides 60 (or 50) Hz power to the product under test

Electrostatic Discharge (ESD)• ESD is an example of the complete spectrum of

conducted & radiated susceptibility/immunity

• However, ESD is more than just EMI. It is EMI plus direct charge injection into the victim equipment

• ESD events can be as large as lightning or as small as a spark from finger to door knob or equipment knob

• Sudden flow of electrons between two objects caused by contact or an electrical short

Electrostatic Discharge (ESD)

• Causes of ESD include static electricity and

electrostatic induction

• Creation of static electricity and subsequent

ESD event can be considered a three-step

process:

– A charge is generated on an insulator

– Charge is transferred onto a conductor by contact

or induction

– The charged conductor comes near an object and a

discharge occurs.

Electrostatic Discharge (ESD)• Understanding charge

transfer is key to understanding ESD

• Charge transfer depends on many things– Materials involved

– Humidity & Temp.

– Existing E fields

• Triboelectric Series helps understand charge transfer (not the same as the Galvanic Series)

• Separation of materials in the series does notnecessarily indicate magnitude of charge created

Order in the series and magnitude of the charges are

dependent upon the properties of the substance, but

these properties are modified by factors such as

purity, ambient conditions, pressure of contact,

speed of rubbing or separation and the contact area

over which the rubbing occurs. [MIL-HDBK-263B, p.

24-25]

Electrostatic Discharge (ESD)

Simple model of human body ESD

In MIL-STD-883G the charged human

body is modeled by a 100 pF capacitor

and a 1500 Ω discharging resistance

Mitigation of the ESD Event

• There are essentially three approaches for

preventing problems caused by an ESD event:

– Prevent the occurrence of the ESD event

– Prevent or reduce the coupling (conduction or

radiation) to the electronic circuitry of the product

(create hardware immunity)

– Improve (or add) inherent immunity to the ESD

event in the electronic circuitry through more

robust software (create software immunity)

Summary

• Immunity/Susceptibility best understood using

the EMC triad of source, path, victim

• Select/Control the EME to minimize unwanted

signals

• Use good EMC design principles to minimize

signals, path and victim issues

• Mitigation can be done to each part of the EMC

triad

• Pick solution approaches that are robust enough

to deal with changes in the EMC triad

References

• Bogatin, E., Signal Integrity – Simplified,

Pearson Education, Inc., Upper Saddle River,

NJ, 2004.

• Duff, W., Designing Electronic Systems for

EMC, SciTech Publishing, Inc., Raleigh, NC,

2011.

• Kaiser, K., Electromagnetic Compatibility

Handbook, CRC Press, Boca Raton, FL, 2005

References

• Morrison, R., Grounding and Shielding: Circuits and Interference, 5th ed., John Wiley & Sons, Inc., Hoboken, New Jersey, 2007.

• NTIA, US Dept. of Commerce, Manual of Regulations and Procedures for Federal Radio Frequency Management, May 2013.

• Ott, H., Electromagnetic Compatibility Engineering, John Wiley & Sons, Inc., Hoboken, NJ, 2009.

• Paul, C., Introduction to Electromagnetic Compatibility, 2nd ed., John Wiley & Sons, Inc., Hoboken, NJ, 2006.

Standards for Spectrum/EME

Measurement & Characterization

• Example Standards and References– IEEE 473-1985: IEEE Recommended Practice for an

Electromagnetic Site Survey (10 kHz to 10 GHz) [13 December 1985, reaffirmed 6 May 1992, administratively withdrawn 3 February 2006].

– ANSI/IEEE C63.4-2009: American National Standard for Methods of Measurement of Radio-Noise Emissions from Low-Voltage Electrical and Electronic Equipment in the Range of 9 kHz to 40 GHz

– IEC 61000 family• IEC/TR 61000-2-1, Electromagnetic compatibility (EMC) - Part 2:

Environment - Section 1: Description of the environment -Electromagnetic environment for low-frequency conducted disturbances and signalling in public power supply systems

• IEC/TR 61000-2-3, Electromagnetic compatibility (EMC) - Part 2: Environment - Section 3: Description of the environment -Radiated and non-network-frequency-related conducted phenomena

• Standards– CISPR 11, Industrial, scientific and medical (ISM) radio-frequency

equipment - Electromagnetic disturbance characteristics - Limits and methods of measurement.

– CISPR 16-1, Specification for radio disturbance and immunity measurement apparatus and methods - Part 1: Radio disturbance and immunity measuring apparatus

– CISPR 16-2, Specification for radio disturbance and immunity measurement apparatus and methods - Part 2: Methods of measurement of disturbances and immunity

– CISPR 16-3, Specification for radio disturbance and immunity measurement apparatus and methods - Part 3: Reports and recommendations of CISPR

– CISPR 16-4, Part 4-1: Uncertainties, statistics and limit modeling —Uncertainties in standardized EMC tests

– CISPR 22, Information technology equipment - Radio disturbance characteristics - Limits and methods of measurement

– CISPR 24, Information technology equipment - Immunity characteristics - Limits and methods of measurement.

Standards for Spectrum/EME

Measurement & Characterization

Documents

Introduction to Immunity and Susceptibility