Conducted Electromagnetic Interference
Encyclopedia
EMI- Electromagnetic Interference: EMI is unwanted effects in the electrical system due to electromagnetic radiation and electromagnetic conduction. Electromagnetic radiation and electromagnetic conduction are differentiated by the way an EM field propagates. Conducted EMI 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.
Due to this EMI, the electromagnetic field around the conductor is no longer evenly distributed and causes skin effect, proximity effect, hysteresis losses, transients, voltage drops, electromagnetic disturbances, EMP/HEMP, eddy current losses, harmonic distortion, and reduction in the permeability of the material.
EMI can be conductive and/ or radiative. Its behavior is dependent on the frequency of operation and cannot be controlled at higher frequencies. For lower frequencies, EMI is caused by conduction and, for higher frequencies, by radiation. For ex: Skin effect is due to the conductive EMI and proximity effect is due to the radiative EMI.
The worst part of a high frequency electromagnetic signal is that it makes every conductor an antenna, in the sense that they can generate and absorb electromagnetic fields. In the case of a PCB (printed circuit board), which consists of capacitors and semiconductor devices which are soldered to the bread board, the capacitors and soldering act like antennas, generating and absorbing electromagnetic fields. The chips on these boards are so close to each other that the chances of conducted and radiated EMI are significant. Bread boards are designed in such a way that the case of the board is connected to the ground and the radiated EMI is diverted to ground. Technological advancements have drastically reduced the size of chipboards and electronics; however, this means they are also much more sensitive to EMI.
The most common solution to EMI is electromagnetic shielding. However, EMI shielding is expensive and has negative consequences. Another method to reduce EMI is to twist wires; however many facilities have tens of thousands of feet of wire, so this is not practical.
A common example of radiated EMI is a cable TV wire and the TV. If you unhook the cable from the TV and place it in front of the plug, video can still be seen on the TV. This is due to electromagnetic signals capable of traveling through the air from cable to TV.
The designers of the distribution system did not have to worry about the compatibility of wire, transformers, heavy machinery, sensitive computers, copy machines, fax machines, server room
s, fluorescent lighting and automated phone systems, all functioning together in one electrical environment. The EM fields of all the various wire and electrical equipment are constantly interfering with each other, degrading performance, degrading efficiency, degrading equipment and degrading wire.
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Due to this EMI, the electromagnetic field around the conductor is no longer evenly distributed and causes skin effect, proximity effect, hysteresis losses, transients, voltage drops, electromagnetic disturbances, EMP/HEMP, eddy current losses, harmonic distortion, and reduction in the permeability of the material.
EMI can be conductive and/ or radiative. Its behavior is dependent on the frequency of operation and cannot be controlled at higher frequencies. For lower frequencies, EMI is caused by conduction and, for higher frequencies, by radiation. For ex: Skin effect is due to the conductive EMI and proximity effect is due to the radiative EMI.
The worst part of a high frequency electromagnetic signal is that it makes every conductor an antenna, in the sense that they can generate and absorb electromagnetic fields. In the case of a PCB (printed circuit board), which consists of capacitors and semiconductor devices which are soldered to the bread board, the capacitors and soldering act like antennas, generating and absorbing electromagnetic fields. The chips on these boards are so close to each other that the chances of conducted and radiated EMI are significant. Bread boards are designed in such a way that the case of the board is connected to the ground and the radiated EMI is diverted to ground. Technological advancements have drastically reduced the size of chipboards and electronics; however, this means they are also much more sensitive to EMI.
The most common solution to EMI is electromagnetic shielding. However, EMI shielding is expensive and has negative consequences. Another method to reduce EMI is to twist wires; however many facilities have tens of thousands of feet of wire, so this is not practical.
A common example of radiated EMI is a cable TV wire and the TV. If you unhook the cable from the TV and place it in front of the plug, video can still be seen on the TV. This is due to electromagnetic signals capable of traveling through the air from cable to TV.
EMI & Electrical Configurations
When there is no return path of current due to an improper electrical configuration, the chance of generating EMI is significantly increased. When the electrical circuit is not complete (no return path of current), the current doesn't know which way to go. This will certainly cause the electrical wire to generate the electromagnetic field into the air as radiated EMI. EMI through the ground wire is also very common in an electrical facility.The designers of the distribution system did not have to worry about the compatibility of wire, transformers, heavy machinery, sensitive computers, copy machines, fax machines, server room
Server room
A server room is a room that houses mainly computer servers. In information technology circles, the term is generally used for smaller arrangements of servers; larger groups of servers are housed in data centers...
s, fluorescent lighting and automated phone systems, all functioning together in one electrical environment. The EM fields of all the various wire and electrical equipment are constantly interfering with each other, degrading performance, degrading efficiency, degrading equipment and degrading wire.
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Standards
A standard specification is an explicit set of requirements for an item, material, component, system, or service. In the EMC field, there are several organizations that set standards for performance. The largest of these organizations are the Institute of Electrical and Electronics Engineers (IEEE), the International Electrotechnical Commission (IEC), the American National Standards Institute (ANSI), and the US Military (MILSTD).See also
- Electromagnetic CompatibilityElectromagnetic compatibilityElectromagnetic compatibility is the branch of electrical sciences which studies the unintentional generation, propagation and reception of electromagnetic energy with reference to the unwanted effects that such energy may induce...
- Electromagnetic InterferenceElectromagnetic interferenceElectromagnetic interference is disturbance that affects an electrical circuit due to either electromagnetic induction or electromagnetic radiation emitted from an external source. The disturbance may interrupt, obstruct, or otherwise degrade or limit the effective performance of the circuit...
- Switched-mode power supplySwitched-mode power supplyA switched-mode power supply is an electronic power supply that incorporates a switching regulator in order to be highly efficient in the conversion of electrical power...
- Proximity effect (electromagnetism)Proximity effect (electromagnetism)In a conductor carrying alternating current, if currents are flowing through one or more other nearby conductors, such as within a closely wound coil of wire, the distribution of current within the first conductor will be constrained to smaller regions. The resulting current crowding is termed the...