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This is a branch of electrical sciences involved with the studies of unintentional generation, propagation as well as reception of electromagnetic energy with a particular reference to electromagnetic Interference, EMI, (unwanted effects) that may come along with that kind of energy. EMC’s main goal is correct operation within a similar electromagnetic environment and avoid interference effects of the equipment that use electromagnetic phenomena. Thus EMC aims at pursuing emission and susceptibility or immunity issues, Eric S. R, and Radke C. J. (1991)
There are different types of coupling mechanisms that includes; conductive coupling, inductive coupling, capacitive coupling, magnetic coupling and radioactive coupling. Conductive coupling takes place when there is a direct contact between the source and the receptor e.g. by a wire, transmission line or a cable. Inductive coupling takes place when there is a short distance (less than a wavelength) between the source and the receiver. Magnetic coupling occurs when there is a varying magnetic field between two parallel conductors that are less than a wavelength apart thus causing a voltage across the receiving conductor.
On the other hand, capacitive coupling takes place when there is a varying electric field between two adjacent conductors less than a wavelength apart. Electromagnetic or radioactive coupling occurs when the source of noise and sink are more than a wavelength apart. The sink and the source act as radio antennae where the electromagnetic waves emanating from the source crosses the open space and is received by the sink, McFee, S and Giannacopoulos, D., (2001).
Cause and effects of EMC
To avoid the direct effect of EMC, it is a requirement to observe certain rules for example switch off electronic devises before taking a flight. In this instance it is required that the electronic systems, equipments and other electrical devises be in a position to operate in a defined margin of safety in their intended electromagnetic environment as well as at levels that do not cause unacceptable degradation due to electromagnetic interference. Devises such as radio transmitters, hand phones, motor drives devices and solid state switching devises cause electromagnetic pollution due to the emissions they give out to the environment. Susceptible electronic equipment will thus be affected by these emissions. It’s thus apparent that the EMC issues cannot be ignored, Martha M. Y., (1991).
There are thus three types of standards that have been provided so as to ensure that the equipments can work as closely as possible. These include; product family standards, generic standards and basic standards. The product family standards define the tests to be carried out, limits or levels, and performance criteria or operating conditions to apply. Whenever possible, the family product standards should refer to the Basic Standards for test. Generic standards relate to a particular environment e.g. commercial, domestic, light industry and Industrial environment. General information on disturbing phenomena, testing and measuring techniques is provided forth by the Basic standards. Although they do not contain performance criteria or limits, they serve as reference for product standards, Erren T.C., (2001).
Electromagnetic noise is usually produced from the source due to a rapid current as well voltage changes and spreads through the coupling mechanisms. Breaking a coupling path has been found to effective both at the start and at the end of a path. Thus most of the good EMC designs apply both to the potential victims as well as to the potential emitters. Since a circuit used to couple energy to the outside world will also couple energy back and thus be susceptible, a design improvement would reduce both the susceptibility and emissions. Some of the design measures taken include: Decoupled Cable Entries (Line filter, Signal filter) by use of RC elements or RF chokes; Shielded Lines; Shielded Housings; and the avoidance of Antenna Structures in PCB Design e.g. loops of unbalanced transmission lines or circulating current.
There are additional measures that can be taken to reduce the emissions. These includes avoiding unnecessary switching operations. The necessary switching should be carried out as slowly and technically as possible. It is recommended that noisy circuits that has a lot of switching activity be physically separated from the rest of the design. Use of harmonic wave filters should also be encouraged. In order to reduce susceptibility, use of fuses, circuit breakers and trip switches as well as transient absorbers should be encouraged, Tsuyoshi, N., et al.. (2007).
Emission issues are concerned with the generation of unwanted electromagnetic energy, the counter measures to be taken to avoid such generation and how to avoid the remaining energy from escaping into the environment. Immunity or susceptibility issues refer to the correct operation in the presence of unplanned electromagnetic disturbances of the electrical equipment. Thus mitigation, noise or Interference and thus electromagnetic compatibility can be achieved by addressing both the susceptibility and emission issues. This implies silencing the sources of interference, having the path between source and victim being less efficient as well as having the potential victim systems to be less vulnerable.
Eric S. R, and Radke C. J. (1991). Electrostatic interactions in colloidal suspensions: Tests of pair wise additivity. AIChE Journal. Volume 37, Issue 6. Pages: 805-824.
Martha M. Y. (1991). System design and cataloging meet the user: User interfaces to online public access catalogs. Journal of the American Society for Information Science Volume 42, Issue 2. Pages: 78-98.
McFee, S and Giannacopoulos, D. (2001). Optimal discretizations in adaptive finite element electromagnetics International Journal for Numerical Methods in Engineering Volume 52, Issue 9. Pages: 939-978.
Erren T.C. (2001). A meta-analysis of epidemiologic studies of electric and magnetic fields and breast cancer in women and men Bioelectromagnetics Volume 22, Issue S5, Pages: S105-S119.
Tsuyoshi, N., Kazuo, S., Kenji, T., Tatsuya, K and Shinji, N. (2007). Structural topology optimization for the design of broadband dielectric resonator antennas using the finite difference time domain technique International Journal for Numerical Methods in Engineering Volume 71, Issue 11, Pages: 1261-1296.