Sandia Research specializes in the development of electromagnetic geophysics solutions using frequencies ranging from HF down to ELF.

Through-the-Earth (TTE) Communications

 

Conventional electromagnetic-based communications methods are not effective in underground and other hostile environments, such as deep building interiors. Military organizations, firefighters, rescue crews, and mine workers need to communicate in these difficult environments. Poor communications in underground environments have too commonly resulted in unnecessary deaths, as evidenced by disasters in the mining industry.

 

Through-The-Earth (TTE) communications is a difficult task. The U.S. Bureau of Mines undertook an extensive effort to develop a TTE electromagnetic trapped miner location and communications system following the 1977 Coal Mine Safety and Health Act. Although tremendous progress was made in this program, a completely satisfactory solution to the problem has not been fully realized. Sandia Research has made breakthrough developments that allow TTE through 2,000+ feet of rock - all using a hand-held, low-powered, radio. The basis of our technique is described in US Patent # 8,462,829.

 

Contact us to discuss your TTE needs.

 

 

Magnetic Dipoles

 

A magnetic dipole is simply a circular loop of current flow. Physically, a magnetic dipole can be created with an n-turn coil.  A loop created by wire lying in the x-y plane creates a z-oriented magnetic dipole.  The vector magnetic moment,M ⃗, is used to characterize the strength of the dipole.  The magnitude of the vector, M, is a function of the area of the loop, A, the number of turns in the loop, N, and the current flowing in the coil, I.  For example, the magnetic vector moment of a coil lying in the x - y plane is:

     M = I  N  A

 

In three dimensions, an arbitrary dipole will be a 3-D vector magnetic dipole.

     M = Mx x + My y + Mz z

 

For low frequencies, this problem may be defined as a quasi-static condition. This means that the fields produced by a magnetic dipole are not near field terms and are not radiating or propagating fields, but rather, they fall in between both such extremes and are labeled quasi-static, where the field properties are a function of frequency and media conductivity. The fields of a magnetic dipole, in cylindrical coordinates, have a vertical and a radial component - but, no azimuthal component.  This fact is exploited in our positioning, surveying and tracking applications.

 

Fields of a magnetic dipole

 

James R. Wait (1972, Trans Antennas & Propagation), originally developed a closed form integral solution for both horizontal and vertical magnetic dipoles in a homogeneous half space model. Sandia followed this with a n-layer solution, again using integral solutions.  The solutions are developed using Hertz vector potentials and result in integral solutions containing Bessel functions.  An example of the solution (for both radial and vertical fields) for a vertical magnetic dipole source in a homogeneous half space is shown below:

Magnetometry

 

A magnetometer is an instrument used to measure the earth's magnetic field strength at a given point on the earth. Ferrous objects such as iron, will distort the magnetic field of the earth. The earth's magnetic field is measured in nano-Telsas (NT) and can vary in magnitude from approximately 20,000nT at the southern coast of Brazil to more than 65,000nT near the north and south poles. The inclination (the angle between the Earth’s field and the horizontal) varies from 90 degrees at the magnetic poles to zero degrees at the equator. On land, magnetometers can be used to find buried ferrous objects such as unexploded ordinance. Marine magnetometers are commonly used to find shipwreck or other submerged cultural artifacts. Marine magnetometers towed behind a survey vessel and are positioned to be as near the bottom as possible.

 

Modern magnetometers are often of the alkaline vapor type, such as cesium and can provide total magnitude readings up to 10 Hz with sensitivities of 0.01 nT. The challenge in analyzing magnetometer data  is locating anomalies that may be 1 nT in a background field of 40,000 nT.

 

Sandia Research has more than 30 years of experience working with magnetometers and magnetic data. During this period we've supported the National Park Service's Submerged Resources Center with both hardware and software solutions.

 

Turrets of the USS Arizona - NPS Divers

MAD SEA Software

 

 

 

 

 

Sandia Research has developed marine Magnetic Anomaly Detection (MAD-SEA) software that automatically detects targets, even with strong regional trends and high frequency noise. MAD-SEA software will be commercially available in early 2017.

 

Full field magnetic data contour plot

3-D plot after processing with MAD-SEA automatic target detection

Contour plot after processing with MAD-SEA automatic target detection

Quality of Survey (QoS)

 

When conducting both terrestrial and marine magnetic survey, there doesn't exist a tool to analyze the quality of a given survey. The major goal of a QoS analysis is to determine the percentage of the survey that would have missed targets of interest. Sandia Research has recently developed a QoS tool for marine magnetometer surveying. In marine survey the following data is needed to conduct a QoS analysis.

 

  • Northing
  • Easting
  • Magnetometer height off bottom (HOB)
  • A noise sample from an anomaly-free area.

 

 

The survey bounding area calculated by a Convex Hull in this figure. Other options include:

  • Imported bounding polygon
  • Axis Aligned Bounding Box (AABB)
  • Oriented Bounding Box (OBB)

QoS results. In this example the target was 100 kg of cast iron with a minimum detection SNR of 6 dB. The red areas show where this target may have gone undetected. In this example, the criteria were meet 98.23%.

Tunnel Detection

 

Sandia Research has been involved in tunnel detection research for nearly three decades. The detection of clandestine tunnels remains a challenging endeavor. Recent breakthroughs by Sandia Research have lead to some innovative methods for both tunnel detection and tunnel  mapping from the surface. Contact us for additional information.