Electromagnetic Interference & Electromagnetic Compatibility


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Electromagnetic Interference & Electromagnetic Compatibility

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  2. 2. INTRODUCTION:  Electromagnetics (EM) is a branch of physics or electrical engineering in which electric and magnetic phenomena are studied.  Electromagnetic interference exist in every communication link.it manifests itself as noise.  Electromagnetic interference (EMI) is electromagnetic energy that adversely affects the performance of electrical/electronic equipment by creating undesirable responses or complete operational failure.  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 intentional EMI.  The most common methods of noise reduction include proper equipment circuit design, shielding , grounding, filtering, isolation, separation and orientation and noise cancellation techniques. 2
  3. 3. EM Signal: E=Electric field B=Magnetic field 3 E B
  4. 4. DEFINITION OF EMI & EMC: EMI???  Electromagnetic interference is the degradation in the performance of a device due to the fields making up the electromagnetic environment. EMC???  Electromagnetic compatibility is achieved when a device functions satisfactorily without introducing intolerable disturbances to the electromagnetic environment. 4
  6. 6. 6 Example: Electromagnetic interference in TV signal
  7. 7. BASIC ELEMENTS OF EMI SITUATION 7 Interference occurs if the received energy causes the receptor to function in unwanted manner. Whether the receiver is functioning in wanted or unwanted manner, depends on the coupling path as well as the source and victim. The medium is to be made as inefficient as possible.
  9. 9. RADIATED INTERFERENCE 9 Narrow band interference usually arises from intentional transmissions such as radio and TV stations, pager transmitters , cell phones etc. It is a high frequency operation . Example: proximity effect Broad band interference usually comes from incidental radio frequency emitters. These includes electric power transmission lines, electric motors etc. It is a low frequency operation Example : skin effect
  10. 10. CONDUCTED INTERFERENCE  Conducted electromagnetic interference is caused by the physical contact of the conductors as opposed to radiated EMI, which is caused by induction (without physical contact of the conductors).  Electromagnetic disturbances in the EM field of a conductor will no longer be confined to the surface of the conductor and will radiate away from it.  This persists in all conductors and mutual inductance between two radiated electromagnetic fields will result in EMI 10
  11. 11. Differences between conducted and radiated interference 11
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  13. 13.  Intra system EMI causes  Inter system EMI causes 13 Effects of EMI Momentary disturbance in TV and radio reception due to operation of mixer- grinder/electric shavers/a passing vehicles etc Reset of computers and loss of data. Change of setting of status of control equipments. Failure of pace maker implemented in a patient due to a „walkie talkie‟ Malfunctioning of flight controlling system due to use of laptop by passenger. Biological hazards.
  14. 14. Sources of EMI: The sources of EMI can be broadly classified into two groups  Natural sources of EMI example: lightning  Manmade sources of EMI example: commercial radio and telephone communications In specific we can classify as  Functional: EMI can originate from any source designed to generate electromagnetic energy and which may create interference as a normal part of its operation  Incidental: EMI can originate from man made sources .These sources are not designed specifically to generate electromagnetic energy but which do infact cause interference.  Natural: EMI can be caused by natural phenomena, such as electrical storms , rain particles , solar and interstellar radiation. 14
  15. 15. 15 Fig:1 Fig: 2 Fig1-lightning hitting between the Buildings. Fig2-lightning hitting a tree
  16. 16. EMI CONTROL TECHNIQUES: To control or suppress EMI, the three common means employed in the design process are Grounding Shielding Filtering 16
  17. 17. Grounding: 17 Grounding is the establishment of an electrically conductive path between two points to connect electrical and electronic elements of a system to one another or to some reference point, which may be designated as the ground. .An ideal ground plane is a zero-potential ,zero-impedance body that can be used as a reference for all signals in associated circuitry and to which any undesired current can be transferred for the elimination of its effects. Bonds provide protection from electrical shock, power circuit current return paths, and antenna ground plane connections, and also minimize the potential difference between the devices. They have the ability to carry large fault current. Bonding is the establishment of a low-impedance path between two metal surfaces. Grounding is a circuit concept, while bonding denotes the physical implementation of that concept.
  18. 18. Shielding:  The purpose of shielding is to confine radiated energy to a specific region or to prevent radiated energy from entering a specific region.  Shields may be in the form of partitions and boxes as well as in the form of cable and connector shields.  Shield types include solid, nonsolid (e.g., screen), and braid, as is used on cables. In all cases, a shield can be characterized by its shielding effectiveness.  The shielding effectiveness is defined as SE=10 log incident power density transmitted power density  where the incident power density is the power density at a measuring point before a shield is installed and the transmitted power is the power density at the same point after the shield is in place. 18 10
  19. 19. Filtering:  An electrical filter is a network of lumped or distributed constant resistors, inductors, and capacitors that offers comparatively little opposition to certain frequencies, while blocking the passage of other frequencies.  Filter provides the means whereby levels of conducted interference are substantially reduced.  The most significant characteristic of a filter is the insertion loss it provides as a function of frequency.  Insertion loss is defined as IL=20 log V2/V1  Where V1 is the output voltage of a signal source with the filter in the circuit, and V2 is the output voltage of the signal source without the use of the filter. 19 10
  20. 20. ELECTRO MAGNETIC COMPATIBILITY  Electromagnetic compatibility (EMC) is the branch of electrical science which studies the unintentional generation, propagation and reception of electromagnetic energy with reference to the unwanted effects (Electromagnetic interference, or EMI) that such energy may induce.  The goal of EMC is the correct operation, in the same electromagnetic environment, of different equipment which use electromagnetic phenomena, and the avoidance of any interference effects.  A system is said to be electro magnetically compatible if :- • It doesn't cause interference with other system . • It is not susceptible to emissions from other systems. • It doesn‟t cause interference with itself.  EMI is a phenomenon while EMC is an equipment characteristic or a property not to generate EMI above a certain limit and not to be affected or disturbed by EMI. The statement "Live and let live" is the best way to describe EMC. 20
  21. 21. The methodologies used to prevent EMI are:-  Suppress the emissions at source point , best method to control EMI.  Make the coupling path as inefficient as possible.  Make the receiver less susceptible to emission. 21
  22. 22. COUPLING MECHANISM: 22 The basic arrangement of noise source, coupling path and victim, receptor or sink is shown in the figure below. Source and victim are usually electronic hardware devices, though the source may be a natural phenomenon such as a lightning strike, electrostatic discharge(ESD) or, in one famous case, the Big Bang at the origin of the Universe.
  23. 23. There are four basic coupling mechanism : 1. Conductive 2. Capacitive 3. Magnetic/Inductive 4. Radiative Conductive coupling: Conductive coupling occurs when the coupling path between the source and the receptor is formed by direct contact with a conducting body, for example a transmission line, wire, cable, PCB trace or metal enclosure. Conduction modes: Conducted noise is also characterized by the way it appears on different conductors:  Common mode or common impedance coupling: Noise appears in phase(in the same direction) on two conductors.  Differential mode coupling: Noise appears out of phase(in the opposite direction)on two conductors. 23
  24. 24. Capacitive coupling:  Capacitive coupling occurs when a varying electrical field exists between two adjacent conductors typically less than a wavelength apart, inducing a change in voltage across the gap. Inductive coupling:  Inductive coupling occurs where the source and receiver are separated by a short distance (typically less than a wavelength).  Strictly, "Inductive coupling" can be of two kinds, electrical induction and magnetic induction.  It is common to refer to electrical induction as capacitive coupling, and to magnetic induction as inductive coupling. Magnetic coupling:  Magnetic coupling (MC) occurs when a varying magnetic field exists between two parallel conductors typically less than a wavelength apart, inducing a change in voltage along the receiving conductor. 24
  25. 25. Radiative coupling:  Radiative coupling or electromagnetic coupling occurs when source and victim are separated by a large distance, typically more than a wavelength.  Source and victim act as radio antennas: the source emits or radiates an electromagnetic wave which propagates across the open space in between and is picked up or received by the victim. 25
  26. 26. NEED FOR EMC STANDARDS:  The EMC standards are required for trouble free co-existence and to ensure satisfactory operation.  They are also required to provide compatibility between electrical, electronic, computer, control and other systems.  Standards are required as manufacturer-user interaction and user‟s knowledge on EMI are limited.  They are also required for establishing harmonized standards to reduce international trade barriers and to improve product reliability and life of the product. 26
  27. 27. EMC STANDARDS: These are of two types  Military Standards : Military EMC standards are made in order to ensure system-to-system compatibility in the real time military environment. Military standards are more stringent than civilian standards. Most of the military standards are broadly based on MIL-STD 461 and 462.  Civilian Standards: The civilian EMC standards are applicable for equipments used for commercial, industrial and domestic applications. The emission standards are specified to protect the broadcast services from interference.. 27
  28. 28. ADVANTAGES OF EMC STANDARDS The advantages are: Compatibility, reliability and maintainability are increased. Design safety margin is provided.  The equipment operates in EMI scenario satisfactorily.  Product life and profits are increased. 28
  29. 29. EMC STANDARDS IN DIFFERENT COUNTRIES: Sl no Standard name Meaning Country 1 CISPR(IEC) Committee International Special Perturbations Radioelectriques – Europe International committee 2 FCC Federal Communications Council USA 3 SAE Society of Automobile Engineers Trade Association Technical Committee 4 VG Military standard Germany 5 VDE Verband Deutscher Electrotecknikev Germany 6 ISI EMI measurements & measuring apparatus India 29
  30. 30. CONCLUSION:  The fact that EMI was recognized as a problem of significant practical concern three-quarters of a century ago generally suggests that by now this must be a well-understood field, and solutions to problems are consequently a routine technology.  The position is that a great deal of theoretical, analytical and practical information is today available to understand EMI, have graduated from the traditional EMC fixes based on trail and error approach.  EMC has developed into a very interdisciplinary subject.  Many problems and topics in this field are how ever still open for further research.  There is aerial need for further research on several aspects of EMC .These include characterization of interferences, measurements techniques etc... 30
  31. 31. REFERENCES:  “Emi protection for communication systems” a textbook by kresimir malaric.  “Elements of electromagnetics” a textbook by Sadiku,3rd edition.  “Applied electromagnetics and Electromagnetic compatibility” a textbook by Dipak L.Sengupta, Valdis V.liepa  http://www.arrl.org/tis/info/rfigen.html RadioFrequency Interference/ElectroMagnetic Interference, ARRL  http://www.kyes.com/antenna/interference/tvibook.html INTERFERENCE HANDBOOK  EMC Testing and Standards in Transient Immunity Testing, RF Immunity. Electronics-project-design.com. Retrieved on 2011-07-19. 31
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