Transcript Nten216_Oct4_06

Oct. 4, 2006
Assignment #2 Marked
Lab #3 due today
Electromagnetic Radiation and Health
Systems
Non-ionizing Radiation
Insufficient energy to cause ionization
High energy non-ionizing radiation still
won’t cause ionization
– Ionizing energy: depends on frequency not
amplitude
– UV frequency: 750-800THz
Sources of Non-ionizing Radiation
Mostly man-made sources
Electronics and electrical devices
– FCC/Industry Canada regulations
High voltage power lines
Mobile phones and base stations
WLANs, bluetooth
Microwave ovens
Cordless phones
Number is growing
Health Effects of Non-Ionizing
Radiation
Thermal – increase temperature of molecules
– Microwave oven
– Smaller scale effect in any RF field
Non-thermal – uncertain as to any non-thermal
effect
– Potentially: damage to cells, DNA, chromosomes
REFLEX study, Cemfec project, Interphone
project, Perform-A project, and others
Measuring EM Exposure
Specific Absorption Rate
– Measures absorption of EM radiation by body
– RF electronics have SAR ratings available to
users
– Less than 1.6watts/kg is max level allowed
Health Effects of Non-Ionizing
Radiation
Independent Expert Group on Mobile
Phones
“Weight of evidence does not suggest that there are
adverse health effects from exposure to RF fields below
guideline levels, but the published research…has
limitations, and mobile phones [and WLANs] have only
been in widespread use for a limited time. The possibilty
therefore remains open that there could be health effects
from exposure to RF fields below guideline levels; hence
more research is needed.”
What then to do?
What then to do?
WHO suggests:
– Take precautions to minimize exposure
– Limit cellphone use
– Limit WLAN use (how do we do that at OC)
– Limit wireless use by children
– Place high power antennas away from people
– Microcell networks
EM and Health Review
What is ionizing radiation?
Name 2 natural sources of ionizing
radiation.
Name 2 man-made sources of ionizing
radiation.
Ionizing radiation is known to be harmful,
why are there any man-made sources of
ionizing radiation.
EM and Health Review (2)
When is non-ionizing radiation harmful.
What is potentially the most harmful source of
non-ionizing radiation that you might encounter?
Is there reason to be worried about the levels of
non-ionizing radiation we are exposed to today?
What about in the future?
Which would you rather be subjected to, 60
watts of 2.4 yoctohertz EM waves, or 60 watts
of 2.4 yottahertz EM waves?
Systems
Systems
Generic Communications Block
Diagram
This diagram generalizes previous one
– Can be used to model entire thing or just a part of it
Qualitatively: System will do something to input
to give output
Quantitatively: If you know any two of the three
parts, you can figure out the third
System Types
Gain/Loss
Filtering/Bandlimiting
Adding Noise
Changing signal type
Modulating/Demodulating
Gain and Loss
SigOutwatts = SysGainabsRatio x SigInwatts
SigOutdBm = SysGaindB + SigIndBm
Filtering/Bandlimiting
System prevents certain frequencies from
passing through
Range allowed is between an upper cutoff
and a lower cutoff
– For low pass filters, the lower cutoff is 0
– For high pass filters, the upper cutoff is infinity
Adding Noise
No signal can be free of noise
No system can be free of noise
NoiseSigOut(watts) = NoiseSystem(watts) +
NoiseSigIn(watts)
Caveat: To do above calculation, noise
must be in watts – you can’t add dBm
together
Changing Signal Type
Converts signal from one type to other
– Continuous ↔ discrete
– Analog ↔ digital
– Periodic ↔ aperiodic
– Deterministic ↔ random
– Finite ↔ infinite
Analog to Digital Converters (ADCs)
Digital to Analog Converters (DACs)
Modulation/Demodulation
Analog Modulation/Demodulation
– AM: Vary signal amplitude to carry data
– FM: Vary signal frequency to carry data
Digital Modulation/Demodulation
– FSK: Use frequencies to encode/decode data
– PSK: Use phase to encode/decode data
– ASK: Use amplitude to encode/decode data