topic 5 electromagnetic environment

8/10/2019 Topic 5 Electromagnetic Environment

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Malaysian Institute of Aviation Technology

ELECTROMAGNETIC

ENVIRONMENT

Topic 5


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Introduction

Any electrical or electronic device creates what is calledan electromagnetic (EM) environment as electrons are

moved around to make the device work.

In addition, there may be natural phenomena such as

lightning occurring in the same location.

Or for one of a variety of reasons, an electrostatic

discharge may take place even when a device or system

is not in its normal functioning mode.

When engineers first became aware of the effects of

such phenomena, in the earliest days of radio, they

usually referred to radio frequency interference (RFI).


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Electromagnetic Environment

Effect

Today, the term electromagnetic interference (EMI)

better reflects the fact that electrical and electronic

systems may cause disturbances at any frequency

between 0 Hz and the GHz (microwave) range.

Electromagnetic effect :

- Electromagnetic Interference (EMI)

- Electromagnetic Compatibility (EMC)

- Electrostatic Discharge (ESD)- High Intensity Radiated FreqUency (HIRF)


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The Electromagnetic Spectrum


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Frequency bands used in EMI measurement


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Electromagnetic Interference (EMI)

Electromagnetic interference (or EMI, also called radio

frequency interference or RFI) is a (usually undesirable)

disturbance that affects an electrical circuit due to

electromagnetic radiation emitted from an external

source.

The disturbance may interrupt, obstruct, or otherwise

degrade or limit the effective performance of the circuit.

The source may be any object, artificial or natural, that

carries rapidly changing electrical currents, such as anelectrical circuit or from the Sun.


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The internal circuits of personal computersgenerate EM fields in the RF range.

Also, cathode ray tube (CRT) displays generateEM energy over a wide band of frequencies.

These emissions can interfere with theperformance of sensitive wireless receiversnearby.

If you have a wireless receiver of any kind and

use it at the same time as you operate yourpersonal computer, you will probably hear RFnoise in the receiver that originates in the PCsystem.


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Malaysian Institute of Aviation TechnologyELECTROMAGNETIC COMPATIBILITY

(EMC)

Electromagnetic compatibility (EMC) isthe studies ofunintentional generation, propagation and reception ofelectromagnetic energy with reference to the unwantedeffects (Electromagnetic interference, or EMI) that suchenergy may induce.

The goal of EMC is ensure the correct operation, in thesame electromagnetic environment, of differentequipment which use electromagnetic phenomena, andthe avoidance of any interference effects.

EMC problemscan occur when the system which is

being adversely affected is subject to a high fieldstrength due to a radio transmitter. These effects are notdue to defects in the transmitter (other than poor RFshielding), transmitter defects such as harmonics areconsidered in Radio transmitter design.


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The sensitivity of a device, or adjacent devices, to theentry of electromagnetic fields is described by the use ofthe terms susceptibility or immunity.

Susceptibilityor immunityissues, in contrast, refer to

the correct operation of electrical equipment, referred toas the victim, in the presence of unplannedelectromagnetic disturbances.

Interference, or noise, mitigation and henceelectromagnetic compatibility is achieved primarily by

addressing both emission and susceptibility issues, i.e.,quieting the sources of interference and hardening thepotential victims.


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Malaysian Institute of Aviation TechnologyExample - HIRF Generation


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Method to minimize HIRF effects

Protection of critical electronics system residing

the same area, the following method are carried

out

Metal boxes can prevent entry of EMI waves to

interface with systems components.

Proper shielding of wiring systems to preventinterference caused by stray electromagnetic energy

Use fiber optic data buses which are not subjected to

interference such as EMI


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1. Shielding assist in eliminating EMI by

i)Protecting the primary conductor with anouter conductor called the shield bygrounding both ends of the shield.

ii)The braided shield carry effecting anyinduced EMI directs to ground thuspreventing system inaccuracies or failure

2. Shielding is also used when one unit isto be protected from the effects of HFcurrent in an adjacent unit or protection

from HIRF generated by airborne orfound equipment. (Electromagneticcompatibility)


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Malaysian Institute of Aviation TechnologyMaintenance Practices

All wiring, plugs, sockets, and screening

on the aircraft should be inspected as laid

down in the maintenance schedule andthe AMM.

The inspections are normally visual but will

require bonding testing where necessaryand the use of specialist test equipment

where specified in the AMM.


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Malaysian Institute of Aviation TechnologyVisual Inspections

To check for damage, deterioration,

contamination, sign of burning, security,

open circuits, correct assembly, correcttorque of plugs/sockets, locking, chafing,

corrosion, broken strands, broken

screening, etc.

All wires shields, ground leads, screen

jumpers are to be intacted.


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An aircraft passing close to an area of charge can initiatea discharge and this may occur some distance from athunderstorm.

Lightning strikes on aircraft commonly occur within 5,000

feet of the freezing level. Lightning is accompanied by a brilliant flash of light and

often by the smell of burning, as well as noise.

A lightning strike can be very distressing to passengersbut physical damage to an aircraft is rare and is not likelyto threaten the safety of the aircraft.

Damage is usually confined to aerials, compasses,avionics, and the burning of small holes in the fuselage.


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Malaysian Institute of Aviation TechnologyEFFECT

Aircraft Damage -Structural damage to aircraft fromLightning strikes is rare and even more rarely of a naturethat threatens the safety of the aircraft. Nevertheless,there have been many incidents of lightning strikesleaving puncture holes in the radomes and tail fins of

aircraft (entry and exit holes) and damage to controlmechanisms and surfaces.

Crew Incapacitation -Momentary blindness from thelightning flash, especially at night, is not uncommon.

Interference with Avionics -A lightning strike can effectavionics systems, particularly compasses.

Engine Shutdown -Transient airflow disturbanceassociated with lightning to cause engine shutdown onboth FADEC and non-FADEC engines with close-spaced

engine pairs.


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METAL PROTECTED AREAS B777


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The End

topic 5 electromagnetic environment

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