Electromagnetic Interference Ppt

Electromagnetic Interference (EMI)  A disturbance that affects an electrical circuit due to

either electromagnetic induction or electromagnetic radiation emitted from an external source.  Radio Frequency Interference (RFI) is a special class of EMI in which radio frequency transmissions (usually narrow-band) cause unintentional problems in equipment operation.

 EMI is any undesirable electromagnetic emission or any electrical or

electronic disturbance, man-made or natural, which causes an undesirable response, degradation in the performance of electrical equipment  The fundamental concept of electrical and electromagnetic interference involves an emanating source and an affected device or system.  The transfer of energy between systems can occur through radiation, conduction, or induction.  The actual transfer of energy is facilitated respectively through a transmission path, conductive path, or through magnetic coupling.

 Electromagnetic Interference (EMI) is the result of

electromagnetic (E/M) emissions. Every piece of electrically powered equipment transmits and receives E/M energy  Conductors are better antennas as the frequency increases  Since LANs operate at very high speeds there can be lots of problems due to EMI

Electromagnetic interference in analog TV signal

Propagation of emi  Electro-magnetic interference propagate through

conduction over signal and power lines and through radiation in free space.

Sources of EMI   

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Sources of emi can be separated in following catgoriesIncidental interference External noise Inter modulation distortion Spurious emission Adjacent channel interference Environmental interference

Incidental Interference  When a device is unable to distinguish desired signal

due to the reception of a strong signal.  Result of the issues relating to circuit design,shielding requirements etc which lead to the inability to reject these unwanted signal.  Incidental EI have potentially devastating effects on medical devices and airplane electronics.

External Noise  It can be electromagnetic or electrical in nature.

 Noise from electromagnetic source can vary in

intensity and period.  Electrical sources are constant in narure.

Spurious Emission  Transmission of signals that are outside the prescribed

frequency band of a transceiver are considered spurious emissions.  It involves harmonics at multiples of fundamental frequency.

Types of EMI  Depending on the frequency ranges over which an interference

extends, it can be classified into two types: Narrowband interference  Broadband interference  Helps in analysing the effects of emi .

Narrowband Interference  Narrow band interference is electromagnetic radiation

broadcasted by TV and radio stations, as well as cell phones.  These types of interferences are confined to certain select frequency bands and are therefore known as narrow band electromagnetic interferences.  Narrowband interference usually arises from intentional transmissions such as radio

transmitters, cell

and TV stations, pager

phones, etc.

Effects of Narrowband interference  Mobile phones are one of the cases of its effects.  Mobile Phone causes speaker interference any time when it

has an incoming call or is connecting to the service after being shut off.  It causes speakers to sort of blip in and out on the nearby speakers

Cause of the problem  Narrowband electromagnetic interference is the culprit in this case.  Mobile phone must emit electromagnetic waves (like microwaves, x-

rays, or radio waves) to communicate with a tower.  This communication is kept open all the time, and is increased when on a call, or when the phone switches from one tower to the next.  As the phone sends and receives bursts of electromagnetic waves from the tower, the waves impart voltage in a circuit which makes cut-out silence, or noises from the speakers.

Broadband interference

The power density of electromagnetic interference in an average urban environment since 1945.

CAUSES OF EMI