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.