EEE381B Aerospace Systems

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EEE381BAerospace Systems Avionics

• Electromagnetic Interference and Electromagnetic
  Compatibility (EMI/EMC)

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Outline

• Introduction
• Standards
• EMC testing
• EMI Hardening
• Exercises

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1. Introduction 1
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1.1 Definitions

• Electromagnetic compatibility the ability of a
  device, equipment or system to function
  satisfactorily in its electromagnetic environment
  without introducing intolerable electromagnetic
  disturbances to anything in that environment1.
  
• EMI/C is a technical and managerial concern, a
  commercial and a military concern, a safety and a
  legal concern, a legislative and a contractual
  concern, an operable and an interoperable concern
  

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1.2 History

• Much of the research and practice has is roots in
  the military / aerospace industry
• EMC is not new to the commercial electronics
  industry, but the introduction of a 1990s
  European Union directive on requirements for all
  manufactured and imported electronic products has
  resulted in a recent surge in interest world
  wide.

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1.3 Multidisciplinary

• EMC engineering activities involve a large number
  of disciplines
• Electrical engineering
• Systems engineering / project management
• Physics
• Mathematical modeling
• Test labs and test engineering
• Quality assurance
• Legal

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1.4 Sources of EMI 1
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1.4.1 Continuous versus Transient EMI1
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1.4.2 Typical EMI characteristics1
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1.5 Intersystem EMI

• Intersystem compatibility concerns the compatible
  operation of the equipment with all other systems
  with which it must operate or interact with,
  including its environment.
• For example in a military context, it may imply
  that restrictions are placed upon how close an
  aircraft may fly to a ground based transmitter.

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1.5.1 Illustrative Intersystem EMI1
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1.6 Intrasystem EMI

• Intrasystem compatibility refers to the
  compatibility among each of the subsystems that
  are required to operate as a whole. Each
  subsystem must not interfere with any other, and
  each must be free of interference.
• The design of military equipment in this regard
  is highly regulated by specific equipment
  standards.

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1.6.1 Illustrative Intrasystem EMI1
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2. Standards

• Numerous commercial (civil) and military
  standards exist to guide and govern
  electromagnetic compatibility.
• The broad objective of each is to ensure that
  electromagnetic compatibility is achieved (and
  assured) by requiring equipment manufacturers to
  design for and built to acceptable levels of
  interference and protection.

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2.1 A sample of national standards1
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2.2 MIL-STD-4611
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3. EMC Testing

• There exists an enormous range of EMC testing
  strategies and tests specific to each of the
  commercial and military standards. The following
  slides show a small sample of typical test
  set-ups, and are illustrative only. In each,
  look for the equipment under test (EUT) and
  consider the complexities involved in isolating
  and estimating the parameters of interest
• Lab 4 provides a small glimpse into this complex
  field.

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3.1 EMC test philosophy1
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3.2 EMC test activities1
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3.2.1 Emission and susceptibility1
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3.2.2 Electrostatic discharge1
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3.2.3 Radiated emissions / susceptibility1
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3.2.4 Conducted emissions / susceptibility1
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4. EMI Hardening

• In the commercial electronic industry the trend
  is to design a system so as to suppress the EMI
  at the source, (clean power supplies,
  screened/filtered subsystems, low radiation
  devices).
• Military designs on the other hand tend to
  contain the emissions by screening, shielding and
  filtering cables and whole subsystems.

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4.1.1 Shielding1
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4.1.1 Filtering1
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4.2 Conclusion

• EMI/EMC is a highly specialized field of
  engineering. Within military aviation it may
  limit operations, it is an essential
  consideration with nearly every aircraft
  modification, and it is a significant effort with
  any new development or installation.
• The support of expert advice and specialist
  agencies is customary, however ignorance of
  EMI/EMC effects is not a legitimate excuse.

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5. In-class exercises
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5.1 Sources of EMI

• Consider the modern day suburban home. List three
  sources of EMI, and evaluate the potential
  impact.
• Now consider a modern military aircraft. Lit
  three sources of EMI.

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5.2 System EMC

• Consider a project such as the Electronic Support
  and Trainer (Challenger). What intersystem and
  intrasystem EMI/C concerns are there when
  equipping a commercially certified aircraft with
  powerful EW jammers and receivers covering
  communications bands HF, UHF, VHF, as well as
  radar bands C/D, E/F, G, I ?

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References

• David Morgan, A Handbook for EMC Testing and
  Measurement , IEE Electrical Measurement Series
  8, Peter Peregrins Ltd, 1994.
• Mark A. Hicks, "Clip art licensed from the Clip
  Art Gallery on DiscoverySchool.com"