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Module 5b > 5.14 Electromagnetic Environment > Flashcards

5.14 Electromagnetic Environment Flashcards

1
Q

What are the 3 elements of any electromagnetic compatibility issue?

A

Source, Receptor, Path Between them.

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2
Q

How are electromagnetic compatibility problems solved?

A

By identifying at least 2 of these elements and eliminating one of them.

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3
Q

What are the 4 methods of coupling electromagnetic energy from a source to a receptor?

A
  1. Conducted (electric current)
  2. Inductively (Magnetic field)
  3. Capacitively (Electric field)
  4. Radiated (Electromagnetic field)
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4
Q

At distances greater than one-sixth of the wavelength of the frequencies of concern what happens?

A

E (electric) fields and M (magnetic) fields COMBINE into EM Electromagnetic fields.

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5
Q

What is the most important protection from lightning strikes?

A

Electrical bonding

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6
Q

Describe “Noise”

A

Man man electromagnetic generated by motors, generators and other machinery.

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7
Q

Describe direct and indirect effects of lightning damage.

A

Direct = Structural damage
Indirect = Induced transients distrupting electrical equipment.

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8
Q

On an antenna what provides the lightning protection?

A

Mounting bolts create a path to ground.

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9
Q

What must we be careful with in regards to High intensity radiated field HIRF

A

They are man made sources of electromagnetic radiation generated EXTERNAL to the aircraft considered possible interfering with safe flight.

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10
Q

Define Electromagnetic Compatibility EMC

A

Capability of equipment to operate in intended area.

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11
Q

Define Electromagnetic environment.

A

Electromagnetic phenomena existing at a given location.

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12
Q

EMI (Electromagnetic interference) is defined by NATO as?

A

Any electromagnetic disturbance that interrupts, obstructs or otherwise degrades or limits the effective performance of electrons/electrical equipment.

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13
Q

What causes EMI Permeation?

A

Inadequate shielding or damaged shielding/corrosion

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14
Q

What is the most difficult EMI to detect?

A

Radiated electromagnetic energy entering an adjacent device.

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15
Q

What mechanisms are there for energy transfer to affected devices?

A

Radiation, Conduction and Induction.

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16
Q

When dealing with Radiated EMI what are the 3 options?

A

Remove “source”, Harden Target “receptor”, separate devices “path”

17
Q

Effective shielding of avionic devices must anticipate

A

Radiated Susceptibility and Radiated Emissions.

18
Q

What are some techniques for managing interference?

A
  1. Reflecting signals
  2. Reducing entry points.
  3. Absorbing in permeable materials.
    4.Dissipating as heat.
  4. Conducting EMI along the skin and shunting to ground.
19
Q

How is EMI shielding achieved?

A

1.Plating the skins of cases and cable shields.
2. Building up the density of shield material
3.Eliminating line of site entry points.

20
Q

What is the purpose of shielding?

A

To capture the EMI and take it to ground or dissipate signal as heat.

21
Q

How are magnetic waves shielded below <30 KHz?

A

Highly permeable material.

22
Q

How are magnetic waves shielded above >30KHz?

A

Reducing entry windows and ensuring good earths.

23
Q

What are the benefits of Braided shields?

A
  1. Increased structural integrity
  2. Good flexibility/life
  3. Higher percentage of coverage = more effectiveness against high frequency’s.
24
Q

Describe Foil Shields

A
  1. Made from aluminum foil laminated to polyester.
  2. 100% cable or comp coverage.
  3. Commonly used to shield individual pairs in cables to reduce cross talk.
25
Q

Foil and braided shielding when used together can provide?

A

Maximum field efficiency across frequency spectrum

26
Q

Multi shielding provides?

A

Superior attenuation that is effective from kilohertz to the gigahertz.

27
Q

To prevent electromagnetic interference being radiated from signals present IN wires what should be the layout of braiding?

A

Inner = low perm material
Outer = high perm material.

28
Q

The low permeability shield should always be closest to?

A

Source of interference.

29
Q

Low permeability shield provides?

A

Good shielding at high frequencies.

30
Q

High permeability shield provides?

A

Excellent shielding at low frequencies.

31
Q

What methods are used to propagate EMI caused by Radiation?

A

Shielding, Filters & Ground.

32
Q

What methods are used to propagate EMI caused by Conduction?

A

Wire routing & loops.

33
Q

What methods are used to propagate EMI caused by Induction?

A

Distance and shielding.

34
Q

What helps reduce EMI in a printed circuit board?

A

Continuous ground plane.

35
Q

What is a completely enclosed conductive surface called?

A

Faraday cage.

36
Q

What is the goal of the structure shielding?

A

Seal all cracks and holes to make it as close to a faraday cage as possible.

37
Q

What effect does EMI have on fibre optics?

A

Nothing it is immune.

Module 5b (3 decks)

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