EM Day 1.pptx

33 Pages·2013·5.75 MB·English

by  Jamesina Simpson

Why Study Electromagnetics?

Prof. Jamesina Simpson
Department of Electrical and Computer Engineering
University of Utah, Salt Lake City, UT
www.ece.utah.edu/~simpson
Communications in the Mid-1800’s
Letters, Horses, Trains… and

Telegraph Wires
Ø  Electrical telegraph wires over land
(1830’s and 1840’s)
Ø  Transatlantic telegraph cable (1866)

Source: National Archives NWDNS-77-
F-194(6)(62), ca.1862-ca.1863
Photographer, Russell, Capt. Andrew J.
How are signals transmitted down
telegraph wires at fractions of a second?
How Long Will it Take
for an Electron to Travel 1 cm?
Ø  Copper wire, cross-sectional area A = 32 mm2
(assuming an ~1863 telegraph wire of ~1/8” radius)
Ø  Average drift velocity of these conduction electrons:

1
v =
Ane
Charge of an electron
Valence-electron density
€ (number of atoms per unit
volume)
Drift Velocity of the Electrons

Ø  Using n = 8.4 x 1028 free electrons/m3, we get
v = 2.3 x 10-6 m/s
It takes 72 minutes for the
electrons in this wire to drift 1 cm!
What about a wire that is 1000 km long?

Tagging an electron at one end of the wire, it
would take 12,800 years for the tagged
electron to arrive at the other end!
Explanation

Ø  We can infer from this that signals on wires are not
transmitted via traveling electrons.
Ø  Instead, signals are transmitted by way of an electromagnetic
wave just outside the wire.
Ø  And we can extend this to modern day applications, such as
microstrip or striplines in computers!
Maxwell’s Equations and the
Electromagnetic Spectrum
Source: http://
en.wikipedia.org."
Maxwell’s equations apply to electromagnetic wave phenomena from
DC to light. Let’s look at some examples…
Finite-Difference Time-Domain (FDTD)
Computational Electrodynamics
FDTD has become one of the most widely used methods for solving
Maxwell’s equations to investigate electromagnetic wave guiding,
radiation, and scattering phenomena and technologies.

Military Defense Application Example:
Interaction of a 100-MHz Radar Beam with a Prototype Fighter Jet
The study of
Electromagnetic
waves has grown to
include much more
than military
applications.
Source: A. Taflove, Computational Electrodynamics: The Finite-Difference 

Time-Domain Method, Norwood, MA: Artech House, 1995."