Lecture no.1 emi new

OMEGA SEMESTER 2013/2014 SESSION

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VOMATTHEWS 2014 EIE521CU

ELECTROMAGNETIC INTERFERENCE

& COMPATIBILITY -EIE 521-

Today's electronic equipment must satisfy a host of global regulations

that limit a given device's susceptibility to EMI, as well as EMI

emitted by the device itselfHigher electronic clock or operating

frequencies make EMI more difficult to control. As business and consumer electronics incorporate greater functionality and elevated

operating frequencies, their emissions often exceed specified

limits.

COURSE OBJECTIVE

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OBJECTIVE CONT’ED

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At the end of this course you will be able to:

1.Outline the general principle of the electromagnetic compatibility,

2.List the various areas of EMI influence in the environment,

3.Differentiate between sources and victims of EMR,

4.State the courses of EM Interferences and various ways of eliminating or reducing it’s influence.

ELECTROMAGNETIC INTERFERENCEFUNDARMENTALS

EMIF

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Faraday’s Laws of Electromagnetic Induction (discovered in 1831) are :

1. A changing magnetic field induces an electromagnetic force in a

conductor;2. The electromagnetic force is

proportional to the rate of change of the field;

3. The direction of the induced electromagnetic force depends on

the orientation of the field.

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RFI/EMI electromagnetic radiation is made of both electric (E) and magnetic (H) fields.High-frequency radiation tends to have a

large electric field component; low-frequency radiation tends to have a large

magnetic field component. High current devices produce magnetic

fields that could cause interference problems.

GENERAL THEORY

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Electromagnetic radiation involves electric (E) and magnetic (H) fields.

Any change in the flux density of a magnetic field will produce an electric

field change in time and space (Faraday's Law).

This change in an electric field causes another change in the magnetic field

due to the displacement current (Maxwell).

A time-varying magnetic field produces an electric field and a time-varying

electric field results in a magnetic field.

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It is possible for electromagnetic energy from an emitter to adversely

affect electronic devices not designed to work with the emitter?.

This is called Electromagnetic Interference (EMI).

A common example of EMI is when a two-way radio, such as a walkie-talkie, transmits a signal near a television.

The radio signal can be received through the television’s antenna,

distorting the picture and masking the sound with the radio operator’s voice.

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VOMATTHEWS2007 EIE521

EXAMPLES OF EMITRANSMISSION LINES - unintentional activation or explosion of electro explosive devices apart from presenting radiation hazards to humans. MAINS POWER SUPPLY- impair the operation of computers and many IT products.SWITCHES AND RELAYS- Affects telephone circuit and radio telescopesTELEPHONE EQUIPMENT - picks up transmissions from nearby television stations

EXAMPLES OF EMI CONTD…

AIRCRAFT NAVIGATION- affects navigational equipment during takeoff and landing

BIOLOGICAL EFFECTS- induces steady current, surging of shock current through the body and induce electrochemical process and voltage in human body

MILITARY EQUIPMENT- causes missile launch failure.

INSECURE COMMUNICATIONS -intelligence bearing signal can be analyzed by sensors which leads to insecure communication.

EXAMPLES OF EMI CONTD…

INTEGRATED CIRCUITS- sometimes burnout the devices. In digital circuits -increases BER or malfunctions the circuit and in analog circuits -increases noise levels and degrades the operation of circuits and systems.

RADIO ASTRONOMY- Weak radio signals from pulsars and distant galaxies are difficult to detect.

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SOURCES OF EMI

CELESTIAL EM NOISE:

DISCRETE SOURCES- sun, moon and Jupiter. They emit broadband as well as narrowband EM noise. continuous sources like galaxy emit broadband EM noise. cosmic noise does not vary with time.OTHER SOURCES: Intense point sources -radio stars, pulsars, radiation from neutral hydrogen clouds.

CELESTIAL EM NOISE

•Affects sensitive low noise receivers using high gain antennas

especially at VHF, UHF and higher frequencies.

TERRESTRIAL NOISE

ATMOSPHERICS

LIGHTNING DISCHARGE cloud to ground discharge cloud to cloud discharge

ESD

EM FIELDS PRODUCED BY LIGHTNING

Clouds capture charges from the atmosphere.When the field intensity in a charged cloud exceeds the breakdown level, the result will be an electric discharge. discharge -cloud to ground and cloud to cloud.


Clouds capture charges from the atmosphere.When the field intensity in a charged cloud exceeds the breakdown level, the result will be an electric discharge. discharge -cloud to ground and cloud to cloud.

CLOUD TO GROUND DISCHARGE

The total discharge between cloud and the ground- flash, with series of high current pulses -strokes.

preliminary breakdown in the cloud sets the stage for negative charge to be channeled toward the ground in a series of short luminous steps called stepped leader. A fully developed stepped leader causes a downward movement of about 5 coulombs of negative charge cloud with velocity of about 2x 10e8 m/s. The pulse currents are of the order of 1 KA .

CLOUD TO GROUND DISCHARGE CONTD…

As the leader tip with a negative potential of 10e8 volts approaches the ground, initiates an upward moving discharge. The contact between the upward moving and downward moving discharges connects the leader tip to the ground potential. This is called return stroke and has an upward velocity of about one third the velocity of light.

CLOUD TO CLOUD DISCHARGE

Static charges acquired by a cloud produce a static electric field. The duration of electric and magnetic field transients caused by lightning processes is of order of a fraction of a microsecond.excite resonances in the body of an aircraft , digital electronics circuits are susceptible to damage.


A natural source of EMI can be considered as a time dependant current dipole.


LIGHTNING DISCHARGE:

cloud to ground -vertical column of current cloud to cloud -horizontal column of current and cross section of the current column very small.In the far field zone, D>>dl,

In the near field zone, D<<dl, where all terms except last term are significant.

EFFECTS ON TRANSMISSION LINE

Without arrestors it produces 30kv-40kv in a std power line.With arrestors voltage on the line is around 300-400v.

ESD PHENOMENA AND EFFECTS

Accumulated static electric charges are discharged and produces EMI.

Static electricity is generated when two materials of different dielectric constants rub against each other. e.g.; wool and glass

MATERIALS THAT EXHIBIT ESD

CHARGE ACCUMULATION & DISCHARGE –E.G.

a person wearing shoes with soles made of an insulating material (polyurethane foam) walks over a carpet (wool or any synthetic material).result in a voltage of up to 15kv and upper limit to a voltage a person can attain is about 35kv.

OTHER EXAMPLES:

Wheel chairs, rolling furniture, conveyor belts, cooling fans, plastic roller blades, paper movement in copiers and printers, cleaning with an air gun, packaging with PVC layer using hot air blast, cleaning with solvent, thermal blankets, rockets and exhaust nozzles.

Electromagnetic radio frequency (RF) emitters are common in everyday life. They work by sending invisible

electromagnetic energy into the air or down a wire. RF emitters are used in a variety of

applications, including wireless communication, navigation (e.g., Global Positioning System), radar, etc. Some familiar examples of RF emitters include broadcast radio transmitter towers, cellular phones, two-way radios, microwave ovens, weather radars, police radars, cable television, and local area networks. 31


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RFIs can damage electronics (see next slide) and/or cause them to malfunction, even in ways

that compromise built-in, fail-safe mechanisms.

The impact of the malfunction depends on what equipment is affected, how it is affected,

when it is affected, and what function it is performing.

If the affected electronics control critical processes, the impact may be significant,

resulting in economic loss, reduced defenses, and infrastructure facility downtime.

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Standards governing electromagnetic compatibility commonly refer to EMI/RFI, or electromagnetic

interference/radio frequency interference.Such interference is caused by stray voltages and/or

currents coupling between electronic systems creating undesirable effects.

These undesirable effects can vary between a brief annoyance, such as a vacuum cleaner disturbing the family television viewing, to more serious situations, such as a cellular phone interfering with the controls of a machine tool, or a noisy power supply interfering

with the proper operation of an industrial robot.With the increased emphasis on electronic technology,

electromagnetic interference/radio frequency interference is a growing concern.36


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SO EMI IS WHAT???

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• The widespread use of small, high speed electronic devices which are often operated near other electrical systems, as well as the explosion in the number and variety of wireless communication devices available, has resulted in concern about interference effects.

• Faster and more complex circuits are being crowded into ever smaller spaces, increasing the likelihood that devices containing such systems will adversely affect one another.

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Modern electronic devices must therefore be able function

properly in an increasingly cluttered electromagnetic

environment.Thus, the minimization of

electromagnetic interference and susceptibility has become

a major design objective.

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• Often the effects of electromagnetic interference are not discovered until product testing occurs.

• The resolution of interference problems in the late phases of product development often involves the addition of extraneous components which add to system complexity and reduce reliability.

• Additionally, it is illegal to sell products which do not meet government regulations regarding electromagnetic emissions.

• It is therefore desirable that electromagnetic interference issues, and compliance with federal regulations regarding emissions and susceptibility, be

addressed in the initial stages of product design.

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PLEASE NOTEIt should be remembered that effects

described by fundamental electromagnetic principles are always present, and are simply more pronounced under certain

conditions. "Non-ideal behaviour" is, in fact, a

misnomer, because it implies that devices are functioning in an abnormal way, when

they are really behaving in a perfectly natural way. It is only through the

application of fundamental principles that the behaviour of devices under all operating conditions is predictable.

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WHERE IS THE CHALLENGE?What makes the task of producing

electromagnetically compatible systems particularly difficult is

that, in addition to understanding the broader principles which govern device behaviour, the

designer often cannot anticipate what types of interference devices will encounter, and must prepare

for all contingencies.

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For these reasons, systems must be designed not only to

minimize emissions, but also to be immune from external

interference. Unfortunately, as the electromagnetic

environment becomes more complex, this goal becomes

more difficult to achieve.

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INTENTIONAL RADIATORS•Intentional radiators are devices which emit electromagnetic energy as part of their desired function. These include such devices as radio and radar transmitters, cellular phones, remote controls for car alarms, etc. •Because intentional radiators emit signals by design, their operation may interfere with other electronic devices. •Example, digital computers may interpret radio or television signals as data, resulting in spurious commands being executed.

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UNINTENTIONAL RADIATORS•Unintentional radiators are devices which are not designed to radiate but still emit electromagnetic energy. These include digital devices, motors, relays and switches, etc.•An intentional radiator such as a cellular phone may also be an unintentional radiator at frequencies other than those at which it normally transmits.

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A BRIEF HISTORY OF EMC/EMI•Until the early part of the twentieth century, few man-made sources of electromagnetic radiation existed.• While the first crude radio receivers tended to be susceptible to interference from natural noise sources, the correction of this problem was usually a relatively simple task. •Conflicts between early radio transmitters were easily resolved by changing frequencies or by simply moving the transmitter or receiver.

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• In the years that followed, more and more man-made sources of electromagnetic radiation began to appear.

• At nearly the same time that it became possible to transmit and receive complex, information-carrying signals via radio, television, and telephones, the increased generation and use of electricity caused a proliferation of noise sources such as dc motors, ac power lines, relays, and fluorescent light bulbs .

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• World War II saw the introduction of radar and other remote sensing systems, along with the use of radio communication in combat. Instrumental in the development of radar was the introduction of small microwave sources, such as the cavity magnetron.

• This and other relatively small electronic devices, were incorporated into vehicles such as ships, airplanes, and automobiles.

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In the early 1960's, MIL-STD-461 was imposed, regulating not only electromagnetic emissions, but susceptibility as well. Also in the years following World War II, CISPR produced various publications dealing with recommended emissions limits, which were adopted by some European countries

• Have already been used to defeat security systems,• Commit robberies,• Disable police communications,• Induce fires,• Disrupt banking computers.• Improvised RFWs have been demonstrated to jam

satellites, • Cause a catastrophic failure in a locomotive and damage

automobiles. • Devices that can be used as RFWs have unintentionally

caused aircraft crashes and near-crashes,• Pipeline explosions, large gas spills, computer damage,

medical equipment malfunctions,• Vehicle malfunctions such as severe braking problems,

weapons pre-ignition and explosions,• Public water system malfunctions that nearly caused

flooding.

EMI EVIL

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For example, utilities and manufacturing facilities have become increasingly reliant upon automated control systems such as supervisory control and data acquisition (SCADA) systems and distributed control systems (DCS) to monitor, control, and regulate their processes. These automated control systems are basically composed of various electronic subsystems including a master computer called a Master Terminal Unit (MTU), a remote processor/controller called a Remote Terminal Unit (RTU). 55


Communications using wireless radio or telephone lines, electronic sensors (pressure sensors, current meters, etc.), and electronically controlled actuators (e.g. valves, circuit breakers, etc.) and relays, as shown in in the next slide. RFIs can potentially be used to affect any of these electronic devices and produce effects such as unintentional valve closures, disabled communications, false data transmissions, and damage to the electronic device itself.

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Further complicating matters, the data displayed on a control monitor ( Next Figure) may not reflect the actual state of the system, which may hamper the operator’s ability to correct the problems. Impacts from such effects can range from nuisance (e.g. having to send a technician to a remote site to reset equipment) to catastrophic (e.g. gas pipeline ruptures/explosions and mass electric power outages). 58


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EMI DEFINATIONSThe International Eletrotechnical

Vocabulary (IEV) definition's on

EMI/EMC

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According to the International Electro technical Vocabulary

IEV 161-01-07, EMC is the ability of a device or system to

function satisfactorily in its electromagnetic environment without introducing intolerable electromagnetic disturbances

to anything in that environment.

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In recent years, several trends have together made EMC more important than ever: • Disturbances are becoming stronger with increasing voltage and current values.• Electronic circuits are becoming increasingly sensitive.• Distances between sensitive circuits (often electronic) and disturbing circuits (power circuits) are becoming smaller.

• Electromagnetic Compatibility (EMC) is the ability of electrical or electronic equipment/systems to function in the intended operating environment without causing or experiencing performance degradation due to unintentional EMI.

• It is recommended that the performance be tested or qualified to insure operation within a defined margin of safety for the required design levels of performance.

• The EMI source minus the coupling mechanism path losses should result in an emission level that is less than the victim's susceptibility threshold minus a predetermined safety margin.

The goal of EMC is to minimize the influence of electrical noise.

EMC DEFINITION

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Electronic equipment can malfunction or become totally inoperable if not designed to properly minimize the effects of interference from the

internal and external electromagnetic environments.

Proper equipment and system designs are also necessary for minimizing potential electromagnetic

emissions into the operating environment.

It is important that electronic equipment designs ensure proper performance in the expected

electromagnetic environment, thus maintaining an acceptable degree of Electromagnetic Compatibility

(EMC).

EMC CONT….

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SOME (EMI) DEFINITIONS CONT.

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Attenuation in terms of EMC ,this is the reduction of an electromagnetic field across a shield (usually expressed in decibels (dB) at a given frequency).Cutoff Frequency is the maximumpossible frequency beyond which thewaveguide will no longer shield EMI

• Electromagnetic Emission is theenergy radiated to the environment

from an electronic product.• Electromagnetic Immunity is the

ability of an electronic product to function in its environment in the presence of electromagnetic radiation.

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Electromagnetic interference: Interference to the operation of communications products or

other electrical and electronic devices generated by all electrical and electronic

products or natural causes.

Electromagnetic interference: The interference by electromagnetic signals that can cause

reduced data integrity and increased error rates on transmission channels.

Electromagnetic Frequency Interference: - Unwanted "noise" created by current-producing devices such as electric motors and fluorescent

lights. EMI effects the quality of the signal passing through data transmission medium.

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Electromagnetic Effects (EME) includes many electromagnetic

environmental disciplines such as Electromagnetic Compatibility

(EMC), Electromagnetic Interference

(EMI), and Electromagnetic Pulse (EMP)68


Shielding Effectiveness (SE) is the measure of protection provided by

an enclosure against electromagneticinterference at a specific frequency. It is

generally expressed in decibels (dB), where.

SE = 20 Log (EO/EI)EO (V/m) is the measure of field strengthwithout the shield; EI (V/m) is the field

strength with the shield in place

SHIELDING EFFECTIVENESS

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Decibel (dB) in terms of EMC is adimensionless logarithmic ratio

used as amanageable value of measurement

for thereduction or attenuation of

electromagneticinterference.

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Most high frequency wave energy is reflected off a conductive wall.

In the low frequency range, however, the magnetic waves can penetrate the shield.

For low frequency magnetic-dominant noise, therefore, the absorption

characteristics of the shield become much more important.

The absorption characteristics are related to the magnetic permeability and wall thickness of the shielding material.

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When two sinusoidal electromagnetic waves of the same wavelength reach the same location at the same time, the superposition principle

says the net electric field at that location is the vector sum of the electric fields in each wave. (The same is of course true for the magnetic fields; we will talk only about electric fields

here, because they are responsible for most of the interaction of electromagnetic radiation

and matter.)

THE SUPERPOSITION PRINCIPLE AS APPLIED TO ELECTROMAGNETIC

RADIATION

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EMI, or electromagnetic interference can be a problem to

designers of many products. Personal Computer manufacturers must design to meet the FCC Part

15 regulations to prevent PC's from interfering with other office

equipment.(In Nigeria there is no standard for

EMI !!!)

WHY DO ELECTROMAGNETIC FIELDS NEED MAGNETIC

SHIELDING?

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• Cell phone designers have to incorporate RFI shielding to stop unwanted RF emissions as well as to prevent other electrical equipment from interfering with the cellular telephone's operation.

• Designers may find that densely packed electronic assemblies may have internal components that interfere with each other, requiring electro magnetic shielding.

• When the electromagnetic interference includes low frequency radiation, magnetic shielding is essential to assure proper operation of the electronic equipment.

For an Electromagnetic

Interference or EMI condition to exist, the following conditions

must be present:

NOTE

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There must be a source. An interference source is called an "emitter" of electromagnetic energy.

The emitter may propagate electromagnetic energy either intentionally, like a hand held

radio, or unintentionally, like a power transformer.

There must be a device sometimes referred to as the "victim", that is susceptible to the

electromagnetic energy being emitted by the emitter source.

If the susceptible device does not have sufficient immunity to reject the energy it is being exposed

to, electromagnetic interference may occur.

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A physical relationship must exist between the two devices wherein they share a common

propagated electromagnetic field. The physical distance between devices and their

spatial orientation with respect to each other may have a significant role in determining

whether the devices will react with each other. The sensitivity of a device to EMI is described

by either susceptibility or immunity. Since susceptibility to EMI varies with many factors,

devices can be placed into an active electromagnetic field without user awareness

that a potential EMI problem may exist. Adjacent devices may also unintentionally radiate electromagnetic fields that can, in

turn, affect other devices.

CONDITIONS

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A FEW CONCEPTS

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Everyone knows the fire triangle; well here we have a variation on it, the EMI triangle.As with its predecessor, remove any of the 3 sides and the EMI problem goes away.

Electromagnetic interference occurs when three elements come together:

A source of interferenceA receiver of the interference

A path of transfer.According to this simple scheme, minimizing the electromagnetic interference can be attained by

eliminating one of the three elements:82


CONCEPT CONT’ED

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The so called source-path-receptor model is illustrated in the slide before, suggests that electromagnetic interference can be prevented in one of three ways:- suppress emissions at the source- interrupt or reduce the efficiency of the coupling path- make the receptor immune to emissions

(For the purpose of this explanation I have used the radiated propagation

method)

SO HOW DO YOU DO THAT?

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Coupling paths are typically classified as belonging to one of four general classes:•CONDUCTIVE•RADIATIVE•INDUCTIVE•CAPACITIVE

Causes of EMI can be intentional or inadvertent, hostile or friendly, military or civil, and either

foreign or domestic. They can come from a jamming device,

malfunctioning equipment, or improper system operation.

Regardless of the cause or intent, the effect is always the same—interference of our

electromagnetic emissions. Electronic jamming, while not common in our everyday operations, is nonetheless a potential

threat against which we need to be ever ready to guard and overcome.

What occurs much more frequently than is generally realized is interference from extraneous navigation

and telecommunications systems, and other sources .

OTHER SOURCES

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INCREASE THE DISTANCE

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EMF causes electromagnetic interference or "EMI" with a large variety of sensitive

equipment: DC magnetic fields from subway rail lines can disrupt computer monitor

displays. ELF or AC magnetic fields from a building's

electrical system can interfere with computer systems.

RF from nearby broadcast antennas can interfere with wireless LAN systems, IT

equipment and highly sensitive equipment. With the pervasive increase in EMF sources

throughout the world, there is a corresponding increase in concern that human exposure to

EMF may cause adverse health effects.

OTHERS

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OTHER METHODS

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Microwave towerThe majority of EMI concerns are centered on radio frequency (RF) emission sources

due to the massive global increase in personal computers, digital pagers, hand-

held radios, cellular phones, wireless devices, etc.

Although most RF transmissions are achieved under controlled conditions, it is this transmitted energy that may create an

interference producing phenomenon, a phenomenon that may affect the

performance of many electronic devices.

INTERFERENCE FROM RADIO FREQUENCY FIELDS

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Transient Electromagnetic Fields are produced by the switching of inductive loads such as circuit breakers

or motors. Lightning will also cause this type of disturbance. A transient signal in a cable produces a radiated

emission with a spectral content dependent on the amplitude, rise time and pulse width.

The reception of broadband fields at the lower frequencies is mainly via cables, which are electrically

long with respect to the wavelength. A cable longer than one quarter of a wavelength will

be an efficient receptor. Broadband radiation from transient sources is rarely

found to have significant energy at frequencies exceeding 500 MHz. 94


Conducted interference may originate from the coupling of ambient radiated interference or may be capacitive, inductively or galvanically induced in the cable by an emitting source. At audio and lower radio frequencies, EMI is primarily caused by conduction. The impedance presented by power cables, cable screens, etc. is generally low and this type of EMI will be readily propagated.

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Unfortunately, the potential of an EMI threat from elevated AC magnetic fields to computer and telecommunications equipment is not well

understood. While there are numerous antidotal reports of EMI problems with routers and distribution systems from external AC magnetic fields,

very few manufacturers of such equipment or systems provide meaningful sensitivity or

immunity specifications or guidelines. Moreover EMI guidelines for AC magnetic

field immunity thresholds are internationally inconsistent.

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As a precautionary measure, several major industrial and financial services companies have established internal

guidelines which recommend that computer equipment including

cabling, data-hubs, network controllers, servers, etc. should not be operated in environments where AC magnetic field levels exceed 20 to 30

mG. 97


In patient-connected medical electronics, immunity to external radio-frequency

interference (RFI) is one of the toughest electromagnetic interference (EMI)

problems to handle. Patient-connected devices are often placed

in high-noise environments and often perform life-critical functions.

And one of the most difficult EMI issues to address is protecting analog signals from RFI generated by a nearby handheld radio

or cellular phone. 98


Three main elements contribute to the problem. First, physiological processes emit very weak

signal levels, which makes the signals vulnerable to RFI.

Second, the input signals are impossible to shield adequately because the end of the cable connected to the patient cannot be terminated.

Third, leakage current limitations restrict capacitive filtering to the ground, thereby

prohibiting the most effective method of RFI filtering.

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THANK YOU

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