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Applications of high sensitivity magnetometers:
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A magnetometer is used to measure the strength of the Earth’s magnetic field. To
get a feel for the sensitivity of these magnetometers, the earth’s magnetic
field strength in London on 24 SEP 2005 was 48,489 nT, increasing by 31.43 nT
per annum. The 0.1 nT accuracy of the potassium magnetometer is very close to
the 0.086 nT daily increase in the earth’s magnetic field strength, in London.
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geophysical surveys measuring the minute variations in the Earth’s magnetic
field strength, to identify the location of mineral Kimberlite pipes and provide
hints as to the location of hydrocarbon deposits
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compliment seismic surveys, in oil and gas exploration work
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detect underground metallic structures, such as pipes, tunnels, barrels, items
of archaeological importance
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detect the presence of metallic structures in dense foliage, such as trucks,
pipes, crashed aircraft, artefacts from lost civilisations, using differential
magnetometry
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detect metallic structures under rivers and oceans, such as pipes, ship wrecks
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detect the presence of intruders in dense undergrowth, such as armed militia,
with metal guns, possibly travelling on metal bicycles, motorbikes, or, in metal
trucks…
The Earth's total magnetic field intensity in nT.
from
http://www.gemsys.ca/PDFDocs/MM3_GEM_Brief_Review_of_Quantum_Magnetometers.pdf
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Sensor noise as a function of frequency
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from JamesMacnae presentation at SEG 2006
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Typical Detection Range For Common Objects
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Ship 1000 tons
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0.5 to 1 nT
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at 244 m
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Light Aircraft
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0.5 to 2 nT
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at 12 m
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Pipeline (12 inch)
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1 to 2 nT
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at 60 m
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Pipeline (6 inch)
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1 to 2 nT
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at 30 m
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Automobile
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1 to 2 nT
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at 30 m
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100 Kg of iron
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1 to 2 nT
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at 15 m
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45 Kg of iron
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0.5 to 1 nT
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at 9 m
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4.5 Kg of iron
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0.5 to 1 nT
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at 6 m
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0.45 Kg of iron
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0.5 to 1 nT
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at 3 m
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Screwdriver 125 mm
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0.5 to 2 nT
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at 4 m
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- from
http://www.heritagegeophysics.com/Magnetometers/Magnetometers.htm
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Characteristics of some magnetic field sensors
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sensor
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accuracy
in pT
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noise level
in fT/sqrt(Hz)
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solid state magnetoresistance
eg. Honeywell HMC1001 / HMC1002
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350,000
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180,000
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Fluxgate 3 axis magnetometer
eg. Bartington Mag-03
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250,000
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~6,000
low noise ver
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Cesium beam magnetometer
eg. Scintrex CS-3L
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2,500
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600
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Potassium beam magnetometer
eg. Gem Systems GSMP-30A
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100
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700
high sens option
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low temperature (liquid Helium) SQUID
eg. Supracon
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only noise limited
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3.5
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For reference, the Earth’s magnetic field strength at London on the 24
th
September 2005 was 48,489,000 pT.
Magnetic field strength is often quoted in Gauss. 1 Tesla = 10,000 Gauss.
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The Honeywell magnetoresistance sensor
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- from Honeywell application Note An211.pdf as found on
www.magneticsensors.com
site.
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The Bartington Mag-01 and Mag-03 Fluxgate Magnetometer
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.
Above: the Mag-01 instrument.
- from
http://www.bartington.com/
Above and below: the Mag-01MS from
http://www.bartington.com/
Above and below: the Mag-03MC from
http://www.bartington.com/
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Example of a Potassium Magnetometer: GEM Systems GSMP-30
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Small experimental Cesium magnetometer from NIST
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- from Electronics Weekly, 9th January 2005
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The SQUID = Super Conducting Quantum Interference Device magnetic field sensor
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from “LTS SQUIDS: …” by A. Chwala et al,
www.supracon.com
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Comparative sensor noise during winter atmospheric (“sferic”) disturbance
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From James Macnae presentation at SEG 2006
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