wireless applications of the elf range eecs 4390: wireless and mobile networks robert hannan laura...
TRANSCRIPT
Wireless Applications of Wireless Applications of the ELF Rangethe ELF Range
EECS 4390: Wireless and Mobile EECS 4390: Wireless and Mobile NetworksNetworks
Robert HannanRobert HannanLaura BottLaura Bott
James JonesJames Jones
Frequency ClassificationsFrequency Classifications
ELF extremely low frequency 3Hz to 30Hz 100'000km to 10'000 kmSLF super-low frequency 30Hz to 300Hz 10'000km to 1'000km ULF ultra-low frequency 300Hz to 3000Hz 1'000km to 100kmVLF very low frequency 3kHz to 30kHz 100km to 10kmLF low frequency 30kHz to 300kHz 10km to 1kmMF medium frequency 300kHz to 3000kHz 1km to 100mHF high frequency 3MHz to 30MHz 100m to 10mVHF very high frequency 30MHz to 300MHz 10m to 1mUHF ultrahigh frequency 300MHz to 3000MHz 1m to 10cmSHF super-high frequency 3GHz to 30GHz 10cm to 1cmEHF extremely high frequency 30GHz to 300GHz 1cm to 1mm
Extra Low FrequencyExtra Low Frequency
< 1 Hz – 300 Hz< 1 Hz – 300 Hz
Not commonly used in Not commonly used in communicationcommunication
Due to large wavelength, Due to large wavelength, permeates large objects and waterpermeates large objects and water
History of ELFHistory of ELF
Nikola Tesla 1900Inventor 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 Utilization or ELF waveswaves Wireless CommunicationWireless Communication
– Used by the US Navy for submarine Used by the US Navy for submarine communicationcommunication
Tesla briefly transmitted large Tesla briefly transmitted large amounts of power using ELFamounts of power using ELF
Non-destructive testingNon-destructive testing Earthquake PredictionEarthquake Prediction
Properties of Large Properties of Large WavelengthsWavelengths
ReflectionReflection and and scatteringscattering are are relatively negligible for the fact relatively negligible for the fact that the propagating wavelength that the propagating wavelength will be much larger than the will be much larger than the object it impinges upon object it impinges upon
Experience very little path lossExperience very little path loss
24
d
L f
For Example…For Example…
A 100 MHz displays a 56.2 dB path loss in free spaceA 100 MHz displays a 56.2 dB path loss in free space
10 log (4*3.14*100,000/3) = 112.437 dB10 log (4*3.14*100,000/3) = 112.437 dB
compared tocompared to
30 Hz wave with a -9 dB path loss30 Hz wave with a -9 dB path loss
10 log (4*3.14*100,000/10,000,000) = -18.02 10 log (4*3.14*100,000/10,000,000) = -18.02 dBdB
Utilization of ELF in Utilization of ELF in CommunicationCommunication Primarily used by U.S. Navy for Primarily used by U.S. Navy for
communication with submerged communication with submerged submarines.submarines.– The extremely high electrical conductivity The extremely high electrical conductivity
of seawater shields submarines from most of seawater shields submarines from most electromagnetic communications.electromagnetic communications.
– Signals in ELF range, however, can Signals in ELF range, however, can penetrate much more deeply.penetrate much more deeply.
– Low transmission rate of most ELF Low transmission rate of most ELF communications limits their use as communications limits their use as communication channels.communication channels.
US Navy ELF US Navy ELF Communication Communication NetworkNetwork Has Transmitting antennas in Has Transmitting antennas in
Wisconsin and the Upper Peninsula of Wisconsin and the Upper Peninsula of MichiganMichigan
Signal is transmitted into the Signal is transmitted into the atmosphere where it is enclosed atmosphere where it is enclosed between the Earth and the Ionospherebetween the Earth and the Ionosphere
Signal can be transmitted around the Signal can be transmitted around the world at a frequency of 76Hzworld at a frequency of 76Hz
They use SQUID and Tether antennas They use SQUID and Tether antennas for signal receptionfor signal reception
Navy Communication Navy Communication SystemSystem
ELF for CommunicationELF for Communication
AdvantagesAdvantages– Penetrate virtually any objectPenetrate virtually any object– It can Travel Long distances with little path It can Travel Long distances with little path
lossloss DisadvantagesDisadvantages
– Though it travels at the speed of light it Though it travels at the speed of light it has a very low data ratehas a very low data rate
– The size of receiving and transmitting The size of receiving and transmitting antenna is inversely proportional to the antenna is inversely proportional to the frequencyfrequency
Problem StatementProblem Statement
Improve the sensitivity of a Improve the sensitivity of a receiving antennareceiving antenna
Improve the relative size of the Improve the relative size of the antennaantenna
Make an economic receiving Make an economic receiving antennaantenna
Antenna Antenna CharacterizationCharacterization
ELF antennae
Electrical Magnetic
Horizontal Vertical
Tether Ground Rod T-Shaped Ball Tripod
Coil SQUID
Tether and Ground Tether and Ground antennaantenna Measure E-fieldMeasure E-field Too longToo long
– Wavelength of signal at 8 HzWavelength of signal at 8 Hz
– Basic antenna Theory says the antenna should Basic antenna Theory says the antenna should be at least half the wavelength of the signalbe at least half the wavelength of the signal
– That equates to over 100 miles in wire.That equates to over 100 miles in wire.– Impractical because of size and the amount of Impractical because of size and the amount of
noise it would be exposed to over that noise it would be exposed to over that distancedistance
@8Hz 375/ kmfc
Electric Field AntennasElectric Field Antennas
Too longToo long Sensitive to noise and Sensitive to noise and
interferenceinterference Very unpractical Very unpractical Magnetic field antennas (sensors) Magnetic field antennas (sensors)
is a better choiceis a better choice
Various AntennasVarious Antennas
Ball antenna stands over 5’
tall
Coil Antenna about 2 m in length
Stanford’s Elf Magnetic Field Antenna
Magnetic SensorsMagnetic Sensors
Can be small and very sensitiveCan be small and very sensitive
Exhibit a usable signal-to-noise Exhibit a usable signal-to-noise ratioratio
Of interest: Coil antennasOf interest: Coil antennas
SQUIDSQUID
Super Conducting Quantum Super Conducting Quantum Interference DeviceInterference Device
- - Sensitivity threshold magnitude: 10Sensitivity threshold magnitude: 10-14-14 T T
Basic Concept of a DC SquidBasic Concept of a DC Squid
Characteristics of the SQUID
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
Advantages• Very Sensitive to ELF signals
• Can be made light weight and portable
Disadvantages• Has to be Cryogenically cooled
• Very sensitive to environmental noise
• The driving electronics are extremely complex
• Expensive and requires regular maintenance
Coil Antenna
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
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
Loop Antenna• Easy to fabricate
• Inexpensive
• Low maintenance
• Sensitivity of 1 pico Tesla (10^-12)
• Frequency Range of 1Hz to about 1 kHz
Squid Antenna• Complicated driving
electronics
• Highly susceptible to environmental noise
• Cryogenic cooling needed
• Sensitivity of 10^-14 Tesla
• Frequency Range of DC to about 1kHz
Conclusions
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. Researched and became familiar with
Navy communication system and antenna design
2. 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.