Delta ElectroMagnetic Gradiometer

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Delta ElectroMagneticGradiometer
Presented by Larry Stolarczyk, Sc.DStolar
Research Corporation848 Clayton HighwayRaton,
New Mexico 87740(505) 445-3607
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Fundamental Science
Electrical conductor
I
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Electrical Conductivity Frequency Dependence of
Ash Fall Tuff at NTS

• Electrical conductivity of soils and most rock
  increases with frequency
• Signal attenuation rate decreases as the
  operating frequency is decreased

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Attenuation Rate Versus Frequency
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DeltaEM Gradiometer Features

• Provides real-time high-signal-to-noise-ratio
  detection
• Estimates burial depth and center line
• Detects passageways with man-made and
  natural electrical conductors
• Detects at depths ranges from several feet to
  several hundred feet

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Gradiometer Antennas Operating Principles
Electromotive force voltage (emf) produced by
magnetic field (B)
-i N? (?rA) B N number of turns in
coil ?r relative permeability of ferrite
rod ? 2?f and f is operating frequency Primary
wave is suppressed!
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Gradiometer Antennas Schematic
eo emfLMD emfRMD
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Surface Response Over a Long Conductor
Total Field
Gradient
After David Hill, NIST
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Surface Response Over a Sphere
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Delta EMTM Gradiometer Response
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Delta EMTM Gradiometer Features

• DSP processing
• Multiple discrete frequency of operation
• Transflective color display
• GPS receiver with differential WAAS
• Memory card storage
• RF modem
• Telescoping carbon-fiber chassis
• Battery operated

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Delta EMTM Gradiometer Receiver

• Suppresses surface radio frequency
  interference (RFI)
• Detects spreading EM waves
• Detects voids in mines

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Delta EMTM Gradiometer Transmitter
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Delta EMTM Gradiometer Electronics
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Transmit Air-Core Antenna
30-inch diameter loop
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Remote Computer Data Processing

• LabView Graphical Programming
• Three-dimensional spatial plot
• Multiple trace overlay plot

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Delta Mine Test, March 2004
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Emery Coal Mine Test 2005

• Nonintrusive surveys over Emery Coal Mine
• Coal-void boundary information (no known
  conductors)
• Tested areas had 50 to 200 ft of overburden