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Transcript:

Welcome to ECE 3300, Introduction to

Electromagnetics. This lecture is lecture number

three. We're going to be talking about traveling waves.

There are three important factors to

remember about waves. The first is that moving waves

actually carry energy. They carry power and voltage

and current from one location to another. For example,

when a ship passes through water and creates a wave,

that's really an energy source. You can certainly feel it

if you are in a boat near that ship.

The second thing to remember is that waves

have velocity. They move with different speeds in

different media. The very fastest velocity in all of our

applications is going to be in air or in vacuum, and the

third is to remember that they are in linear. They add

up so if I have one wave coming from one direction and

another wave coming from another direction, I can find

the total field at any location just by adding up or

summing these two waves.

Now, there are several ways that we

categorize waves in electromagnetics. One of them is a

function of time. So if we put time on this axis, a

sinusoidal wave would come in and run something like

this so it would be a sine wave. A sine wave is also

called a CW wave. CW stands for continuous wave and

what that means is that we assume that a sine wave has

been going forever. We don't assume that it started at

zero and then we saw it coming, you know, from the

left side. We assume that that has been going forever.

So a sine wave or a continuous wave is sometimes also

called a frequency domain wave because the only thing

that we need to know is the frequency and the

amplitude and then the entire wave is defined.

Now a second type of wave would be something

that changes with time so changes substantially with

time; something like a step function from turning a

source on or off, something like a pulse, perhaps like

this maybe another kind of pulse, spike. Another thing

that you might see is a sine wave something stops. All

of these would be called time domain waves because

there's going to be a substantial variation with time.

Some examples of this would be the electromagnetic

pulses that happen because of a large explosion or

turning things on or off, cell phone signals that turn

themselves on or off, those would be typical examples

of time domain for pulsed or electromagnetic pulsed

simulations. Another way that we can describe waves is

in terms of space.

There are three kinds of waves that we

typically talk about in our electromagnetic classes.

One, for instance, is a one dimensional wave. A wave

that has only one dimension is something that is going

to be continuous in a plane and traveling this way. So

this plane right here is going to be copied and copied

and copied, and the only variance in this wave is in this

one dimension, perhaps in the X direction. This would

be typical of waves that are on transmission lines, and

it's equally applicable to something that we call plane

waves, which we will learn about near the end of our

class, near the end of our course. A plane wave is

something that is constant in two directions, say the Y

and the Z direction, but varies in the X direction. So

those would be 1D waves.

2D waves are waves that vary in two

dimensions. That would be typical, for instance,

suppose that I had a current or some source that was

linear that went from minus infinity to plus infinity.

It's an infinitely long type of system, and then I would

see variation in this plane right here. So in this case,

for instance, the wave would propagate out away from

this current. That would be very much the same as

dropping a stone in the water and having the waves

propagate out from the stone. So that's a two

dimensional wave. These are also called cylindrical

waves and typically, those are caused by very long wire

antennas. An example where you might use antennas

like that would be in geophysical prospecting where you

want to be able to find things that are under the

ground and you use a very, very long wire for that.

A third type of wave is a three dimensional

wave. Most of our realistic situations....

Electromagnetics. This lecture is lecture number

three. We're going to be talking about traveling waves.

There are three important factors to

remember about waves. The first is that moving waves

actually carry energy. They carry power and voltage

and current from one location to another. For example,

when a ship passes through water and creates a wave,

that's really an energy source. You can certainly feel it

if you are in a boat near that ship.

The second thing to remember is that waves

have velocity. They move with different speeds in

different media. The very fastest velocity in all of our

applications is going to be in air or in vacuum, and the

third is to remember that they are in linear. They add

up so if I have one wave coming from one direction and

another wave coming from another direction, I can find

the total field at any location just by adding up or

summing these two waves.

Now, there are several ways that we

categorize waves in electromagnetics. One of them is a

function of time. So if we put time on this axis, a

sinusoidal wave would come in and run something like

this so it would be a sine wave. A sine wave is also

called a CW wave. CW stands for continuous wave and

what that means is that we assume that a sine wave has

been going forever. We don't assume that it started at

zero and then we saw it coming, you know, from the

left side. We assume that that has been going forever.

So a sine wave or a continuous wave is sometimes also

called a frequency domain wave because the only thing

that we need to know is the frequency and the

amplitude and then the entire wave is defined.

Now a second type of wave would be something

that changes with time so changes substantially with

time; something like a step function from turning a

source on or off, something like a pulse, perhaps like

this maybe another kind of pulse, spike. Another thing

that you might see is a sine wave something stops. All

of these would be called time domain waves because

there's going to be a substantial variation with time.

Some examples of this would be the electromagnetic

pulses that happen because of a large explosion or

turning things on or off, cell phone signals that turn

themselves on or off, those would be typical examples

of time domain for pulsed or electromagnetic pulsed

simulations. Another way that we can describe waves is

in terms of space.

There are three kinds of waves that we

typically talk about in our electromagnetic classes.

One, for instance, is a one dimensional wave. A wave

that has only one dimension is something that is going

to be continuous in a plane and traveling this way. So

this plane right here is going to be copied and copied

and copied, and the only variance in this wave is in this

one dimension, perhaps in the X direction. This would

be typical of waves that are on transmission lines, and

it's equally applicable to something that we call plane

waves, which we will learn about near the end of our

class, near the end of our course. A plane wave is

something that is constant in two directions, say the Y

and the Z direction, but varies in the X direction. So

those would be 1D waves.

2D waves are waves that vary in two

dimensions. That would be typical, for instance,

suppose that I had a current or some source that was

linear that went from minus infinity to plus infinity.

It's an infinitely long type of system, and then I would

see variation in this plane right here. So in this case,

for instance, the wave would propagate out away from

this current. That would be very much the same as

dropping a stone in the water and having the waves

propagate out from the stone. So that's a two

dimensional wave. These are also called cylindrical

waves and typically, those are caused by very long wire

antennas. An example where you might use antennas

like that would be in geophysical prospecting where you

want to be able to find things that are under the

ground and you use a very, very long wire for that.

A third type of wave is a three dimensional

wave. Most of our realistic situations....