Slide 1
SCALING THE
ELECTROMAGNETIC
SPECTRUM
Boxing out waves
Slide 2
The First Big Idea
• Scale describes matter and predicts behavior.
During this session we will focus on size
and scale, using the electromagnetic
spectrum as our medium. Size and
scale is the first of nine big ideas of
nanoscale science and technology
recognized by the National Science
Teachers Association (NSTA). Students
deal with size and scale regularly in
both math and science, but
conceptualizing the nanoscale is
difficult even for many adults.
Nanotechnology is defined in part by its
scale, from one to one hundred
nanometers, with one nanometer being
10-9m. The nanoscale is a transitional
zone between the atomic scale and the
micro and macroscales, with which we
are more familiar. Properties of matter
can change significantly as objects
become smaller and move into the
nanoscale. Light waves also exhibit
interesting behaviors as wavelength
gets smaller and as light interact with
matter at the nano scale.
Scale is fundamental to math and
science, and can be represented in
many ways. The EM scale is particularly
suited to the task of illustrating scale.
Wavelength can be measured in metric
units and represented with scientific
notation. The changes in properties of
the EM scale are directly related to
wavelength (scale). This session will
focus on wavelength and frequency.
Slide 3
The “Other” Big Ideas of Nano
• Structure of Matter
• Forces and
Interactions
• Quantum Effects
• Size-Dependent
Properties
Slide 4
Other Big Ideas - continued
• Self-assembly
• Tools and
Instrumentation
• Models and
Simulations
• Science, Technology,
and Society
The next two slides give a brief
overview of the other “Big Ideas”. Size
Dependent Properties involve the
behavior substances at different scales,
and most closely relate to the
characteristics of the EM scale.
Structure of Matter involves the
building blocks of matter from atoms to
molecules to nanoscale structures.
Forces and Interactions at the
nanoscale are dominated by electrical
interactions—gravity and other
Newtonian forces are insignificant.
Quantum Effects related to the
probability of events are also significant
at this scale, and are beyond the scope
of most middle school curricula.
Due to forces and interactions, matter
at the nanoscale tends to selfassemble. Nature has been this way for
millions of years (think biology).
Without Tools and Instrumentation
such as the atomic force microscope,
humans could not “see” or work at the
nanoscale. Models and Simulations are
key to teaching and learning at this
scale because size is so small.
Inventions and innovations impact on
Science, Technology and Society in
potentially positive and negative ways.
Producers and consumers need to be
aware of the potential impacts
(remember asbestos).
Slide 5
• More than you can see
An
Amazing
Scale
Slide 6
Wavelength is the Key
What we see is much less than what we get.
Most people think of light as the colors
of the rainbow—the visible light
spectrum. Visible light is only a small
part of the EM spectrum. Pay close
attention to the video (listen to the
words) and learn some amazing
properties about light beyond what is
visible to our eyes. [Click the picture to
open a link for the video.]
(*Figure Caption: The electromagnetic
spectrum. The red line indicates the
room temperature thermal energy.
*This illustration was made for the
Opensource Handbook of Nanoscience
and Nanotechnology. Illustration by
Kristian Molhave.
Opensource Handbook of Nanoscience and Nanotechnology. Illustration by Kristian
Molhave
What’s important to note here is the
range of wavelength and the associated
energy (inversely related to
wavelength). Visible light is only a
small segment of the spectrum. Radio
waves have very long wavelengths and
low energy (harmless to humans).
Gamma rays have very short
wavelengths and high energy (very
dangerous to humans).
Slide 7
Nanoscale =1 - 100nm
10-7 = 0.0000001 = 100 nm
The lower end of the visible light
spectrum is above the upper end of the
nano scale. We don’t see the light
waves, but we can see the color
reflected off of objects.
Visible Light 390-750nm
Slide 8
10-9 = 0.000000001 = 1 nm
The lower end of the nanoscale
corresponds with the wavelength of xrays. Image of broken leg: from
http://www.sxc.hu/photo/978477
X-ray .01 to 10nm
Slide 9
Waves
• Transfer energy without transferring matter
Open animation at
http://phet.colorado.edu/sims/waveon-a-string/wave-on-a-string_en.html.
Use the applet to complete the activity
Wave Properties. This activity can be
completed as a whole class or small
group activity (provided students have
computers with Internet access).
3.2. Students complete questions 1 and
2 on the Activity Sheet.
Also can demonstrate with a slinky.
Slide 10
Electromagnetic Energy
Determined by wavelength and frequency.
E = mc2
c = 2.9979 x 108 m/s
In the famous equation by Albert
Einstein, energy is related to mass and
the speed of light. All energy in the EM
spectrum travels at the same speed in a
vacuum. Many students have difficulty
with this concept—harmless radio
waves travel at the same speed as
deadly gamma rays. Image by Richard
F. Lyon published under Creative
Commons license.
Light speed is the fastest known speed
in the Universe. A more familiar
expression for students for the speed of
light is 186,000 miles/sec—fast enough
to travel from Earth to the Moon in 1.3
seconds, or from the Sun to Earth in 8.3
minutes.
At the nano scale, all matter exhibits
wavelike properties, so understanding
wave behavior is essential to
understanding nanotechnology.
Slide 11
Dual Nature of Light
• Light is also photons (particles)
• Zero mass and zero rest energy
• Can be destroyed and created
• Can have particle-like interactions with matter
Atoms and molecules are particles.
Atoms are made of smaller particles
(protons, neutrons, and electrons),
which are made of even smaller
particles (quarks). Photons are also
particles, but unlike particles of matter,
they have no measureable mass. They
can also be created and destroyed
when radiation is emitted or absorbed.
They are electrically neutral and unlike
most other particles, the antiphoton is
exactly the same as the photon.
The particle theory of light has been
around since the days of Isaac Newton,
but lost popularity until Einstein
demonstrated the photoelectric effect
required light to have a particle nature.
The dual nature of light (as both
particles and waves at the same time) is
mysterious but essential to
understanding its properties and uses.
From Andrew Zimmerman Jones,
Your Guide to Physics.
http://physics.about.com/od/lightoptic
s/f/photon.htm
Slide 12
Electricity and Magnetism
• Magnetism and electricity move together in the
EM spectrum.
Diagram from Schneider, Remote Sensing and the Global Environment,
http://www.geo.mtu.edu/rs/back/spectrum/
Slide 13
Appearances May Deceive
• Optical properties vary at the nanoscale.
Image source: L. R. Hirsch, R. J.Stafford, J. A. Bankson, S. R. Sershen, B. Rivera, R. E.
Price, J. D. Hazle, N. J. Halas, & J. L. West, Proc. Natl. Acad. Sci. USA, 100, 1354913554 (2003).
Energy in the EM spectrum is both
electrical and magnetic. The
relationship between electricity and
magnetism was long misunderstood.
We know that electricity produces
magnetism and magnetism produces
electricity. In fact, both move together
in waves perpendicular to one another
through the EM spectrum.
Color we see is a measure of light that
is reflected or refracted (not absorbed)
by objects. Gold nanoparticles in
suspension (colloids) of varying
diameters appear different colors as
the particles absorb different
wavelengths of light. [Later in the Nano
Fellows course we will look more
closely at the behavior of light and its
interactions at the nano scale.]
Image source: L. R. Hirsch, R. J.Stafford,
J. A. Bankson, S. R. Sershen, B. Rivera,
R. E. Price, J. D. Hazle, N. J. Halas, & J. L.
West, Proc. Natl. Acad. Sci. USA, 100,
13549-13554 (2003). Anyone may,
without requesting permission, use
original figures or tables published in
PNAS for noncommercial and
educational use (i.e., in a review article,
in a book that is not for sale) provided
that the original source and the
applicable copyright notice are cited.
Slide 14
Blocking Out Signals
This image of a Faraday Cage illustrates
that electrical charges (waves) can be
blocked. Click on the picture to open a
video showing a Faraday Cage in action.
Clicking on a link with the text at the
bottom opens a different video
(airplane struck by lightning).
• Faraday Cage
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Free Documentation License.
Slide 15
Faraday Cage
• How does it work?
Faraday cage was first invented by
Michael Faraday in 1836. The diagram
demonstrates that the charge on a
charged conductor exists only on the
outside (a hollow conductor). These
cages or boxes are made from
conducting material and are used to
protect from EM signals. In a
grounded cage (like that shown on the
previous slide) the excess charges go to
the ground. In an ungrounded cage an
external electrical field causes the
charges to rearrange, cancelling the
electrical field inside the cage.
Effectiveness depends on the
conductivity and thickness of the
material, and the size of the openings.
Image author: Stanisław Skowron.
Public domain.
Slide 16
Blocking Signals Activities
• Materials Needed
• Cell phone or small radio
• Small box with lid
• Aluminum foil
• Aluminum screen
• Scissors
• Tape and/or stapler
• ruler
Slide 16 outlines materials needed for
several experiments to follow. These
materials can vary depending on
availability and student abilities.
Slide 17
Activity – Control Experiment
1. Turn on radio and set in
box.
2. Place lid on box.
3. Turn off radio.
4. One (or more) group test
with cell phone if available.
Slide 18
Activity – Box the Signal
• Wrap box and lid
separately in aluminum
foil (ensure snug fit).
• Set radio in box.
• Open box slightly
(experiment with opening
size).
• One (or more) group test
with cell phone if
available.
Slide 19
Activity – Screen the Signal
• Make a cylinder with
aluminum screen.
• Leave one end open.
• Make a prediction.
• Place radio inside.
• Close other end of
cage.
• Test with a cell phone
if available.
Conduct the Control Experiment
outlined in Step 1 of the Experimenting
With Faraday Cages Activity. You can
save class time by prewrapping the
boxes (not the lids) in aluminum. If you
want to reuse the boxes repeatedly,
you may want to wrap a layer of
polyester film (e.g., Mylar) on top of
the aluminum to protect the aluminum
from tearing. Be careful to leave an
exposed aluminum edge along the top
rim of the boxes if you wrap them in
polyester.
Repeat the experiment (Step 2 in
Experimenting With Faraday Cages
Activity) (Slide 18), but this time have
both the boxes and the tops wrapped,
so that the tops fits snuggly, making a
good connection between the
aluminum on the boxes and tops.
Students complete questions 3 and 4
on the Activity Sheet.
Provide participants with a
square foot of aluminum
screening material. Precut the
material to save time and wrap
the edges in heavy tape (duct
tape) to protect against sharp
edges. Conduct Step 3 of
Experimenting With Faraday
Cages Activity.
Students complete question 5
on the Activity Sheet.
Slide 20
Wavelength and Frequency Activity
• Wavelength
• l = c/f
• C = 3.0 x 108 m/s
Review the relationship between
wavelength and frequency. Have
participants complete questions 6 and
7 on the Activity Sheet.
• Example
l = (300,000,000m/s) /
(540,000 Hz) = 55.6 m
• Frequencies
• AM radio: 540-1640 KHz
• FM radio: 88-174 MHz
• Cell: 850-1900 MHz
Slide 21
What Size Mesh Do You Need?
• Mesh size 1/10 the
wavelength
Slide 22
Activity: Building a Faraday Cage
• Remove foil from top
of box lid.
• Cut several ½” strips of
foil.
• Make a grid of strips
on the lid.
• Experiment with size
openings until a phone
will not ring in box.
Shorter wavelengths have higher
frequencies and energy and are more
difficult to block. To block a signal with
a Faraday Cage using wire mesh, you
need a mesh size about 1/10th the
wavelength. Higher conductive
materials (e.g., copper) work best.
Grid size about 1/10 of wavelength
should screen out the signal. Make
sure strips that are added on the top
make contact with the aluminum on
the sides.
Slide 23
Data Analysis and Conclusions
• When using aluminum
strips, what size
openings worked to stop
the radio? A cell phone?
• Why does the opening
size matter in a Faraday
Cage?
• What other materials
could be used?
Slide 24
Wavelength Matters
• Locations where
wireless equipment
does not work
• Protection from
electronic spies
• Space weather effects
• EMP
Slide 25
Thank You!
The size of the openings that work will
depend on the frequency of the radio
and cell phone and the materials used.
EM waves, unlike sound waves, are
polar. The orientation of EM waves is
usually perpendicular to the direction
of travel. Note that you can reduce a
radio’s reception simply by turning the
radio 90 degrees. Faraday cages can be
constructed to block wavelengths of a
specific frequency (and larger). The
better the conductive material, the
more effective the cage will be.
Discuss why understanding wavelength
and frequency matters. Point out
locations where wireless equipment
will not work due to natural or human
structures. Note the increasing need
for electronic security measures to
protect against theft (financial and
personal information, national
security). Point out that space weather
(radiation from the sun) can create
electronic challenges and beautiful
aurora borealis, and can be dangerous
in space travel. Electromagnetic pulse
(EMP) is being studied as a weapon to
knock out an enemy’s electronic signals
and command structure.