ELECTROMAGNETIC INTERFERENCE (EMI)

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24 Νοε 2013 (πριν από 3 χρόνια και 6 μήνες)

121 εμφανίσεις

ELECTROMAGNETIC
INTERFERENCE (EMI)

Eric Mitchell

Phil
Zanotti

Kasra

Dabiran

Leon
Voskov

Ross Schwarz

OVERVIEW


Introduction


Examples


Wireless Devices


Natural Interferences


Switching Circuits


Radio Frequency


Electromagnetic warfare


Prevention and Mitigations Techniques


Standards and Regulations


Summary



BACKGROUND


What is EMI?



Electromagnetic Interference is disturbance that affects an electrical
circuit


Caused by induction or outside radiation


Can temporary and permanently disrupt circuit components


Big design issue for new products

HOW DOES EMI WORK?


Causes


Electric fields radiating from currents


Switching
circuits, clocks, natural fields,
ect
.


Coupling
of electric fields into circuits and
components


Unintentional and intentional


Effects


Causes problems for electronics


Loss and disruption of data


Growing problem with more advanced devices


EXAMPLES
O
F EMI

SOLAR INTERFERENCE


2012 Solar Maximum


11 year solar cycles


Flight routes over north pole changed


Solar Storm of 1859


March 1989 Solar Storm


X
-
class solar flare


Power outage in Quebec


Communications with some satellites disrupted for hours


Other potential issues


Spacecraft communication


Induced currents on underground piping


HF radio interference


INTERFERENCE AT 2.4
GHZ


Why use 2.4GHz?


Part of the ISM Band


No license needed to design
devices in this range


FCC originally designated
2.4
-
2.483 GHz band for
microwave ovens



Devices and protocols
that operate in this band


Cordless telephones


Baby monitors


Bluetooth


Wi
-
Fi 802.11b and 802.11g
wireless devices (most
routers)


Wireless cameras and
controllers


CELLULAR DEVICE
INTERFERENCE


Airplanes


No proven scientific basis for banning cell phone use on airplanes


FAA
, FCC
, and aircraft OEMs are unwilling to spend money to do
testing


Ban on cell phone use errs on the side of caution


Medical Equipment


2007 Mayo Clinic study showed that phones have no negative effect
on medical equipment


FDA has developed standards for pacemaker OEMs to ensure safety



POWER CONVERTERS


Capacitive, Inductive, and Resistive
loads



Caused by
sudden load
changes



Found in many household items


Computers, p
hone
chargers,
TVs, etc.



Minimal or
no EMI
effect created

ELECTROMAGNETIC PULSE


Intense surge of electromagnetic radiation


Created using high
-
energy explosion (i.e. nuclear)


Gamma rays trap high
-
energy electrons in earth’s magnetic
field


Destroys all power electronics connected to affected
power grid

RADIO FREQUENCY INTERFERENCE


Two way transmitters, radio
stations, amateur radio
broadcast


Interrupted signal before
reaching
receiver


Results in signal masking and
distortion


PREVENTION AND MITIGATION

EMI FILTERS AND CHOKES


Coil of wire wound around magnetic core


Blocks high
-
frequency AC in a circuit


Passive
inductor


Impedance is proportional to frequency


Simple and inexpensive


Energy


Reflected back up the cable


Absorbed resistively within ferrite core (heat)


Audio vs. Radio


ELECTROMAGNETIC SHIELDING

Shields

Examples


Enclosure formed by
conducting material


Isolates electrical devices and
blocks external electric fields


Often known as Faraday Cage
(invented in 1836)


Amount of reduction depends


Material and its thickness


Size of shielded volume


Frequency of fields





Cables


MRI scan room


Microwave oven


Electronic devices

MITIGATION SOFTWARE AND
TECHNIQUES


EMI Analyst

is a tool used for meeting EMI requirements set
by regulatory agencies


Combines all four areas of EMI analysis


Conducted Emissions


Radiated Emissions


Conducted Susceptibility


Radiated Susceptibility


Money Saving Tool


Reduction of circuit design area


FINAL EMISSIONS SCREENSHOT

STANDARDS AND REGULATIONS

EMI TESTING PROCEDURE

REGULATION COMMITTEES

FCC

CISPR


The International Special
Committee on Radio Frequency
Interference


International


House hold appliances, Ignition
systems, fluorescent lamps



Federal Communications
Commission


United States


Modems, Printers, and other
I/O devices

CLASSES OF REGULATIONS

Class A

Class B

“A computing
device that is
marketed for use in a commercial,
industrial, or business
environment; exclusive of a device
which is marketed for use by the
general public, or which is
intended to be used in the home.”


“A
computing device that is
marketed for use in a residential
environment notwithstanding use
in a commercial, business, and
environmental environments.”


FCC AND CISPR CLASS A

FCC AND CISPR CLASS B

OTHER TYPES OF STANDARDS

MIL
-
STD
-
416D

CE
-

Conformité

Européenne


Department of Defense


Even harder
-
to
-
meet standards
than FCC and CISPR


Dependent on reliability of
electronic and communication
equipment



European Conformity


Identifies that a product or
machine is compliant with all
safety requirements


Requirement not a voluntary
process


CONCLUSION


Introduction and Background


Examples of Electromagnetic Interference


Prevention and Mitigation Techniques


Laws and Regulations


Questions?