Wireless Applications of the ELF Range EECS 4390: Wireless and Mobile Networks Robert Hannan Laura Bott James Jones

Frequency Classifications ELFextremely low frequency3Hz to 30Hz 100'000km to 10'000 km SLFsuper-low frequency30Hz to 300Hz 10'000km to 1'000km ULFultra-low frequency300Hz to 3000Hz 1'000km to 100km VLFvery low frequency3kHz to 30kHz 100km to 10km LFlow frequency 30kHz to 300kHz 10km to 1km MFmedium frequency300kHz to 3000kHz 1km to 100m HFhigh frequency 3MHz to 30MHz 100m to 10m VHFvery high frequency30MHz to 300MHz 10m to 1m UHFultrahigh frequency300MHz to 3000MHz 1m to 10cm SHFsuper-high frequency3GHz to 30GHz 10cm to 1cm EHFextremely high frequency30GHz to 300GHz 1cm to 1mm

Extra Low Frequency < 1 Hz – 300 Hz < 1 Hz – 300 Hz Not commonly used in communication Not commonly used in communication Due to large wavelength, permeates large objects and water 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 Wireless Communication –Used by the US Navy for submarine communication Tesla briefly transmitted large amounts of power using ELF Tesla briefly transmitted large amounts of power using ELF Non-destructive testing Non-destructive testing Earthquake Prediction Earthquake Prediction

Properties of Large Wavelengths Reflection and scattering are relatively negligible for the fact that the propagating wavelength will be much larger than the object it impinges upon 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 Experience very little path loss

For Example… A 100 MHz displays a 56.2 dB path loss in free space 10 log (4*3.14*100,000/3) = dB compared to 30 Hz wave with a -9 dB path loss 10 log (4*3.14*100,000/10,000,000) = dB

Utilization of ELF in Communication Primarily used by U.S. Navy for communication with submerged submarines. 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 Has Transmitting antennas in Wisconsin and the Upper Peninsula of Michigan 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 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 Signal can be transmitted around the world at a frequency of 76Hz They use SQUID and Tether antennas for signal reception They use SQUID and Tether antennas for signal reception

Navy Communication System

ELF for Communication Advantages Advantages –Penetrate virtually any object –It can Travel Long distances with little path loss Disadvantages 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 Improve the sensitivity of a receiving antenna Improve the sensitivity of a receiving antenna Improve the relative size of the antenna Improve the relative size of the antenna Make an economic receiving antenna Make an economic receiving antenna

Antenna Characterization ELF antennae Electrical Horizontal TetherGround Vertical RodT-ShapedBallTripod Magnetic CoilSQUID

Tether and Ground antenna Measure E-field Measure E-field Too long Too long –Wavelength of signal at 8 Hz –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 Too long Too long Sensitive to noise and interference Sensitive to noise and interference Very unpractical Very unpractical Magnetic field antennas (sensors) is a better choice Magnetic field antennas (sensors) is a better choice

Various Antennas Ball antenna stands over 5’ tall   Coil Antenna about 2 m in length Stanford’s Elf Magnetic Field Antenna

Magnetic Sensors Can be small and very sensitive Can be small and very sensitive Exhibit a usable signal-to-noise ratio Exhibit a usable signal-to-noise ratio Of interest: Coil antennas Of interest: Coil antennas

SQUID Super Conducting Quantum Interference Device - Sensitivity threshold magnitude: T

Basic 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.