Electromagnetic fields and applications

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16 Νοε 2013 (πριν από 4 χρόνια και 7 μήνες)

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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

Common fields in electrical engineering

An
Electric Field
is produced by charges, and influences other
charges (single charge example)

http://
=2

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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

-
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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://

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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

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=0CFUQsAQ&biw=1097&bih=535

Applications of transmission lines (2)

Optical lens systems

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=2&ved=0CFAQsAQ&biw=1097&bih=535

Applications of transmission lines (3)

Other

What do you think?

Applications of free space EM waves

communications

Radio and television (Analog and HD)

Analog and Digital, AM, FM, SW & Satellite

Two
-

Point
-
to
-

Wire replacement (Bluetooth)

Networked (internet, 802.11)

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

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

Weather monitoring

Speed monitoring

Aircraft monitoring

Surveillance

Remote sensing from space

UTA anechoic chamber

purpose?

All objects emit EM energy according to Planck’s Law

Assessing heat leakage (for example, in a home)

Assessing heating/overheating in devices and systems

Night vision

Antennas

frequency energy

cellular
basestation

example

http://