Now that we understand Electromagnetic Radiation, How do we use it?

1. Now that we understandElectromagnetic Radiation, How do we use it? Information in Waves provided by McGourty and Rideout

2. Four Ways to Encode “Information” • Amplitude • Frequency • Phase • Polarization

3. 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

4. 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”

5. Information in the Amplitude AM radio relies on Amplitude Modulation to encode audio info

6. 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

7. Information in the Frequency The frequency can tell you about the relative velocity of the emitter (Doppler shift)

8. Information in the Frequency FM radio relies on Frequency Modulation to encode audio info

9. Information in the phase 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

10. 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

11. Information in the phase Sometimes used in RFID tags

12. Information in the Polarization • Polarization gives information about the last object the wave bounced off of

13. 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

14. 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)

15. 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

16. Information in the Polarization Satellite communication frequently makes use of polarization to send two separate non-interfering signals at the same frequency

17. Information in the Wave Summary • Amplitude  Intensity • Frequency  Energy • Phase  Timing • Polarization Orientation