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 OF 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?
 Devices and protocols
 Part of the ISM Band
that operate in this band
 No license needed to design
 Cordless telephones
devices in this range
 FCC originally designated
2.4-2.483 GHz band for
microwave ovens
 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, phone 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
 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
Examples
 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
 Federal Communications
Commission
 United States
 Modems, Printers, and other
I/O devices
CISPR
 The International Special
Committee on Radio Frequency
Interference
 International
 House hold appliances, Ignition
systems, fluorescent lamps
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
 European Conformity
 Even harder-to-meet standards
 Identifies that a product or
than FCC and CISPR
 Dependent on reliability of
electronic and communication
equipment
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?