Electromagnetic fields and applications
Dr. Jonathan Bredow
Fields and their applications
• A field relates to the spatial distribution of some quantity of
interest
• The field may be described by a scalar, or it may be described
by a vector
• Pressure example (scalar field)
http://www.usairnet.com/weather/maps/current/barometric-pressure/
Fields and their applications
• Wind direction example
http://www.ambientweather.com/cuunstwimap.html
• Wind direction and barometric pressure are related by the
gradient operator
Common fields in electrical engineering
• An Electric Field is produced by charges, and influences other
charges (single charge example)
http://www.google.com/search?q=electric+field+lines&hl=en&prmd=imvnsfd&tbm=isch&tbo=u&source=univ&sa=X&ei=id5pT6vhIqapsQKStvmOCQ&sqi=2
&ved=0CCwQsAQ&biw=1027&bih=521
Common fields in electrical engineering
• A Magnetic Field is produced by charges in motion, and
influences other charges in motion
http://www.google.com/search?q=magnetic+field&hl=en&prmd=imvns&tbm=isch&tbo=u&source=univ&sa=X&ei=jttpT665D-LQsgLX4dikCQ&ved=
0CF8QsAQ&biw=1027&bih=521
Applications involving electric/magnetic fields
• Influence position or motion of charges by producing fields
(CRT, MRI)
• Sense information about the surrounding electric/magnetic
environment from the fields being produced (Power line
monitoring, Hall-effect detectors), or from how fields are
disturbed (Metal detection, MRI)
• Energy storage (Capacitor – electric field, inductor – magnetic
field)
• Energy conversion – transformers, motors, relays
• Many applications for waves involving electric and magnetic
fields (more coming on this)
Magnetic fields in motors
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/motdc.html
Magnetic resonance imaging
http://en.wikipedia.org/wiki/Larmor_precession#mediaviewer/File:Pr%C3%A4zession2.png
Waves
• Wave - a disturbance or variation that transfers energy progressively from
point to point in a medium and that may take the form of an elastic
deformation or of a variation of pressure, electric or magnetic intensity,
electric potential, or temperature
• http://www.acs.psu.edu/drussell/Demos/waves-intro/waves-intro.html
• Time varying electric fields couple with (result in) time varying magnetic
fields and vice-versa leading to a wave of energy referred to as an
electromagnetic (EM) wave which propagates away from the source at the
speed of light (in open air or vacuum).
• For practical applications EM waves may propagate in free space, or they
may be confined to structures referred to as transmission lines.
Transmission lines
• Circuit models
http://www.google.com/search?q=transmission+lines&hl=en&prmd=imvnsb&tbm=isch&tbo=u&source=univ&sa=X&ei=zyNqT8i1IbHLsQKH_8WVCQ
&ved=0CHgQsAQ&biw=1097&bih=535
Practical transmission lines
• Coaxial line
• Twisted pair
• Microstrip
• Waveguide
• Fiber optics
• Optical lens systems (wave beam modes)
Applications of transmission lines
• Microwave circuits
http://www.google.com/search?q=microwave+circuits&hl=en&prmd=imvns&tbm=isch&tbo=u&source=univ&sa=X&ei=ByhqT7e-JoHctgeTibTkCA&sqi=2&
ved=0CFUQsAQ&biw=1097&bih=535
Applications of transmission lines (2)
• Optical lens systems
http://www.google.com/search?q=compound+lens&hl=en&prmd=imvns&tbm=isch&tbo=u&source=univ&sa=X&ei=mClqT9bmLtLqtgfL1OWPCQ&
sqi=2&ved=0CFAQsAQ&biw=1097&bih=535
Applications of transmission lines (3)
• Other – What do you think?
Applications of free space EM waves –
communications
• Broadcast radio/television
– Radio and television (Analog and HD)
– Analog and Digital, AM, FM, SW & Satellite
• Two-way radio communication
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Point-to-point (Family radio, emergency communications)
Wire replacement (Bluetooth)
Networked (internet, 802.11)
Cellular (CDMA, GSM, 3G, 4G)
Radar: determining range to objects
t = 2R/c, where R is range to the object
http://www.radartutorial.eu/01.basics/rb04.en.html
1 msec corresponds to 150 m
Doppler Shift
- Relationship between wavelength, l, and frequency, f, is c= fl
- Distance traveled during one period
of the waveform is x= v/f
-The apparent wavelength is thus
l’=l – x, or l’ = (c-v)/f
‘
- Hence, the apparent frequency is
f’ = c/l’ = f(1/(1-v/c))
- The Doppler shift is then fd=f’-f
http://imagine.gsfc.nasa.gov/YBA/M31-velocity/Doppler-shift-2.html
Radar applications
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Weather monitoring
Speed monitoring
Aircraft monitoring
Surveillance
Remote sensing from space
UTA anechoic chamber – purpose?
Radiometry
• All objects emit EM energy according to Planck’s Law
• Radiometry applications
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Assessing heat leakage (for example, in a home)
Assessing heating/overheating in devices and systems
Radioastronomy
Night vision
Planck’s Law
http://claesjohnson.blogspot.com/2014/03/the-true-meaning-of-plancks-constant-as.html
Antennas
• Antennas are designed to efficiently radiate or capture radio
frequency energy – cellular basestation example
http://www.google.com/search?q=antenna+images&hl=en&prmd=imvns&tbm=isch&tbo=u&source=univ&sa=X&ei=7jJqT6WmJ
OyGsALe6oyjCQ&ved=0CD4QsAQ&biw=1097&bih=535