Electromagnetic fields and applications

wizzstuffingUrban and Civil

Nov 16, 2013 (3 years and 8 months ago)

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Electromagnetic fields and applications

Dr. Jonathan Bredow

F
ields 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/

F
ields 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)




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


Point
-
to
-
point (Family radio, emergency communications)


Wire replacement (Bluetooth)


Networked (internet, 802.11)


Cellular (CDMA, GSM, 3G, 4G)

Radar: determining range to objects

http://www.radartutorial.eu/01.basics/rb04.en.html

t = 2R/c, where R is range to the object

1
m
sec

corresponds to 150 m

Doppler Shift

-

Relationship between wavelength,
l
, and frequency, f, is c= f
l

-

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 f
d
=f’
-
f



http://imagine.gsfc.nasa.gov/YBA/M31
-
velocity/Doppler
-
shift
-
2.html

Radar applications


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



Assessing heat leakage (for example, in a home)


Assessing heating/overheating in devices and systems


Radioastronomy


Night vision

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