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Now that we understandElectromagnetic
Radiation, How do we use it?
Information in Waves provided by McGourty and Rideout
Four Ways to Encode “Information”
1. Amplitude
2. Frequency
3. Phase
4. Polarization
Information?
• Telecommunication relies on encoding information in one of the four ways
• Probing nature: information is about the source of the wave and/or about the medium it traveled through
Information in the Amplitude
• A higher “amplitude” signal corresponds to a larger number of photons in the quantum view
• In radio astronomy, the amplitude of a signal lets you know the strength of the source
• Your eye perceives amplitude as “brightness”
Information in the Amplitude
AM radio relies on Amplitude Modulation to encode audio info
Information in the Frequency
• Frequency corresponds to the energy gap
• In radio astronomy, the frequency tells you about what the source of the signal is made of (different materials have different energy levels)
• Your eye perceives frequency as color
Information in the Frequency
The frequency can tell you about the relative velocity of the emitter (Doppler shift)
Information in the Frequency
FM radio relies on Frequency Modulation to encode audio info
Phase is the determining factor in how waves interfere
See a cool demo here
In radio astronomy, the phase shift of a wave tells us about the medium through which it traveled
Information in the phase
Information in the phase
In Radio Interferometry, multiple telescopes can create one single, high resolution image if their differing phases are handled properly
Our eyes are insensitive to the phase of a wave
Information in the phase
Sometimes used in RFID tags
Information in the Polarization
• Polarization gives information about the last object the wave bounced off of
Information in the Polarization• Human eyes are
not sensitive to polarization
• Polarized sunglasses work by excluding reflected and scattered light preferentially since they tend to be polarized in certain directions
Information in the Polarization
• Some animals (e.g. bees, ants, fish, octopuses, crickets) are sensitive to polarized light and use it to navigate and enhance their vision
Left Panel presents a normal image of a soft plastic CD case with no polarization information.
Right Panel shows the image with polarization information. The finger print on the CD becomes clearly visible.
(Nader Engheta, University of Pennsylvania)
Information in the Polarization
• In radio astronomy the degree of rotation of a polarized signal (Faraday rotation) gives information about the density of material along the path of the signal
Information in the Polarization
Satellite communication frequently makes use of polarization to send two separate non-interfering signals at the same frequency
Information in the Wave Summary
• Amplitude Intensity
• Frequency Energy
• Phase Timing
• Polarization Orientation