Hi I'm Christopher Young
and my name is Jhonnatan Ascate
and we're both undegraduate students 
at the University of California Davis
and we're here to demonstrate how our project helps visualize electromagnetic waves
First, let's take a look at the
electromagnetic specrtrum
In the electromagnetic spectrum we're 
interested in RF or radio frequency region
Today, radio frequency has become a very
general term that represent electromagnetic waves
From frequencies froma few tens of 
kilohertz to several hundred gigahertz
Radio frequency has many applications
Such as GPS, radio, wifi, cell phones, 
and RADAR
RF waves are actually similar to light in 
that they are both electromagnetic waves
The biggest difference between them is their wavelength and correspondingly their frequency
RF electromagnetic waves fall below the 
visible spectrum
And as far as humans are concerned, 
RF electromagnetic waves are invisible
As the saying goes, "Seeing is believing"
Not being able to see the RF 
eletromagnetic waves
compared to other common forms of 
waves found in nature
Makes it hard for people to
comprehend the concept 
As a counter example, water waves can
be easily observed when we throw a pebble
into a pond
the ripple in this image shows a mechanical wave carried by the movement of the water molecules
In our case, it is the electric and magnetic
fields that carry the electromagnetic waves
In this video, we are going to show our
experiments to visualize RF waves
Using an oscillator, we first generate a
single frequency RF electromagnetic wave
Now if we have a receiver at a distance
"D" away from the transmitter, we can
receive a signal that is represented by
this e_r expression. If we compare the
transmitted signal to the received signal
we can extract the phase difference between
them by applying the signal to a mixer
As we can see, the out of the mixer is 
dependent on the phase, which in turn
follows the amplitude variation of the 
transmitted electromagnetic wave in space
Also as the electromagnetic waves move, 
or propogate through space
the field intensity becomes smaller
according to the inverse of the distance
propagated squared
We also used both RF and base-band amplifiers
to make the signal strong enough to be observed
Now to the part where we actually 
visualize the wave
We use a microcontroller to control 
an array of LEDs 
to display the strength of the mixer
phase difference output
The number of illuminated LEDs is 
proportional to the strength of
the phase difference output of 
the mixer
The color of the LEDs corresponds to 
the sign of the wave amplitude
with positive being blue and 
negative being green.
This means that when the sine wave 
reaches its positive peak, 
all of the green LEDs will be lit up
and similarly when the sine wave
reaches its negative peak, all of the
blue LEDs will be lit up
By moving the receiver back and forth, 
we can see the change in phase difference
and the transition from negative to positive
In this set up, we have the transmitted 
antenna on the floor facing upwards
and are moving the receiving antenna
By moving the receiving antenna slowly, 
we are able to see the transition clearly
If we move the receiving antenna back, 
we are, in a way
tracing the sine wave pattern
with the LEDs
We can then use this this set up to create 
a "light painting" with LEDs in a dark room
This picture is a result of a 30 
second exposure 
during which we slowly moved the
receiving antenna in one direction
We can clearly see the sinusoidal pattern
of the RF electromagnetic wave
You can also see the decaying amplitude
of the sine wave as it propogates
Following in Thomas Young's footsteps
we can perform an interference experiment
by using microwaves instead of 
visible light
and using two transmitters 
instead of slits
By adding a splitter to out schematic, 
we can trasmit through two antennas
instead of just one
With two transmitting antennas stationary
we move the receiving antenna around
and paint the waves in a manner similar
to the previous experiment
So in this video we have shown you our
the invisible RF electromagnetic waves
We hope you enjoyed it
We like to give our special thanks to 
our buddy Huangqing Xiao
From Zhejiang University in 
Hanzhou, China
He was with us during the summer
and worked on the project with us
We'd also like to thank our advisor,
Dr. Xiaoguang Liu
Better known as Leo
And Dr Gregory Charvat from 
Massachusetts for his generous help
With financial help the UC Davis ECE
department and 
MIT's lincoln lab, part of the experiments
you saw today has become
a senior design project at UC Davis
Thank you for watching!
and watch out for a lot more cool 
stuff from us!
