Transcript Wireless Applications of the ELF Range EECS 4390: Wireless and Mobile Networks

Wireless Applications of the
ELF Range
EECS 4390: Wireless and Mobile Networks
Robert Hannan
Laura Bott
James Jones
Frequency Classifications
ELF
SLF
ULF
VLF
LF
MF
HF
VHF
UHF
SHF
EHF
extremely low frequency
super-low frequency
ultra-low frequency
very low frequency
low frequency
medium frequency
high frequency
very high frequency
ultrahigh frequency
super-high frequency
extremely high frequency
3Hz to 30Hz
30Hz to 300Hz
300Hz to 3000Hz
3kHz to 30kHz
30kHz to 300kHz
300kHz to 3000kHz
3MHz to 30MHz
30MHz to 300MHz
300MHz to 3000MHz
3GHz to 30GHz
30GHz to 300GHz
100'000km to 10'000 km
10'000km to 1'000km
1'000km to 100km
100km to 10km
10km to 1km
1km to 100m
100m to 10m
10m to 1m
1m to 10cm
10cm to 1cm
1cm to 1mm
Extra Low Frequency
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< 1 Hz – 300 Hz
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Not commonly used in communication
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Due to large wavelength, permeates
large objects and water
History of ELF
Nikola Tesla 1900
Inventor of AC current
•First to work with ELF
transmission
• Purpose was to Transmit
power
wirelessly in
Colorado Springs
•Was the first to build an ELF
transmitting antenna
Utilization or ELF waves

Wireless Communication
– Used by the US Navy for submarine
communication
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Tesla briefly transmitted large amounts
of power using ELF
Non-destructive testing
Earthquake Prediction
Properties of Large
Wavelengths
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Reflection and scattering are
relatively negligible for the fact that
the propagating wavelength will be
much larger than the object it
impinges upon
Experience very little path loss
 4d 
Lf  

  
2
For Example…
A 100 MHz displays a 56.2 dB path loss in free space
10 log (4*3.14*100,000/3) = 112.437 dB
compared to
30 Hz wave with a -9 dB path loss
10 log (4*3.14*100,000/10,000,000) = -18.02 dB
Utilization of ELF in
Communication

Primarily used by U.S. Navy for
communication with submerged
submarines.
– The extremely high electrical conductivity of
seawater shields submarines from most
electromagnetic communications.
– Signals in ELF range, however, can penetrate
much more deeply.
– Low transmission rate of most ELF
communications limits their use as
communication channels.
US Navy ELF
Communication Network
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Has Transmitting antennas in Wisconsin and
the Upper Peninsula of Michigan
Signal is transmitted into the atmosphere
where it is enclosed between the Earth and
the Ionosphere
Signal can be transmitted around the world
at a frequency of 76Hz
They use SQUID and Tether antennas for
signal reception
Navy Communication
System
ELF for Communication

Advantages
– Penetrate virtually any object
– It can Travel Long distances with little path loss

Disadvantages
– Though it travels at the speed of light it has a
very low data rate
– The size of receiving and transmitting antenna is
inversely proportional to the frequency
Problem Statement
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Improve the sensitivity of a receiving
antenna
Improve the relative size of the
antenna
Make an economic receiving antenna
Antenna Characterization
ELF antennae
Electrical
Magnetic
Horizontal
Tether
Vertical
Ground
Rod
T-Shaped
Coil
Ball
SQUID
Tripod
Tether and Ground
antenna
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Measure E-field
Too long
– Wavelength of signal at 8 Hz
  c / f  375km
@8Hz
– Basic antenna Theory says the antenna should
be at least half the wavelength of the signal
– That equates to over 100 miles in wire.
– Impractical because of size and the amount of
noise it would be exposed to over that distance
Electric Field Antennas
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Too long
Sensitive to noise and interference
Very unpractical
Magnetic field antennas (sensors) is a
better choice
Various Antennas
Ball antenna stands
over 5’ tall
Stanford’s Elf Magnetic Field Antenna
Coil Antenna about 2 m in length
Magnetic Sensors
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Can be small and very sensitive
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Exhibit a usable signal-to-noise ratio
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Of interest: Coil antennas
SQUID
Super Conducting Quantum
Interference Device
-
Sensitivity threshold magnitude: 10-14 T
Basic Concept of a DC Squid
Characteristics of the SQUID
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Frequency detection range is from DC up to
1kHz

Sensitivity threshold of 10^-14 Tesla
Measurements are based on the change in the
H field based on one flux quantum\

*Flux quantum is the amount of magnetic flux from the earth’s magnetic
field passing through an area the size of a human red blood cell.
SQUID Conclusions
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Advantages
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Disadvantages
• Very Sensitive to ELF signals
• Can be made light weight and portable
• Has to be Cryogenically cooled
• Very sensitive to environmental noise
• The driving electronics are extremely complex
• Expensive and requires regular maintenance
Coil Antenna
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High Permeable Ferrite Core
1,000 turns of wire
Sensitivity of 1 pT (10^-12)
Frequency Range of < 1Hz-1kHz
Active Circuit developed by Dr. John
Sutton
Active Circuit
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Patented by Dr. John
Sutton of Goddard
Allows the coil to attract
and bend the incoming
magnetic waves
Small coil absorbs
energy from large
portion of magnetic wave
Comparison of Normal coil antenna
to coil antenna using active circuitry
Comparison of Two Antenae
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Loop Antenna
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•
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Easy to fabricate
Inexpensive
Low maintenance
Sensitivity of 1 pico
Tesla (10^-12)
Frequency Range of
1Hz to about 1 kHz
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Squid Antenna
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Complicated driving
electronics
Highly susceptible to
environmental noise
Cryogenic cooling
needed
Sensitivity of 10^-14
Tesla
Frequency Range of
DC to about 1kHz
Conclusions
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Coil antenna can be used for ELF reception
Using the Introduced circuitry we can improve
on the Navy’s current receiving antenna
The coil antenna will decrease maintenance
and cost of production while maintaining the
required frequency range and sensitivity
Actually the low sensitivity will decrease the
amount of environmental interference
What We DID?
1.
2.
Researched and became familiar with
Navy communication system and
antenna design
Using developed circuitry we propose a
transition for the US Navy to use a loop
antenna using an active circuit as
opposed to the SQUID or Tether.