T HE U NIVERSITY OF W ESTERN AUSTRALIA - S CHOOL OF C OMPUTER S CIENCE AND S OFTWARE
E NGINEERING
CITS4419 Sensors Survey - Magnetic Field
Sensors
Alexander Mazur, 20516281
August 4, 2014
1 M AGNETIC F IELD S ENSORS
A magnetic field sensor, or a magnetometer, is a measurement instrument used to either measure the strength (and possibly direction) of the magnetic field at a point in space, or the
magnetisation of a magnetic material (such as a ferromagnet). [1] Magnetic fields are vector
quantities produced by the movement of electric charges. They indicate the magnetic influence of electric currents and magnetic materials. In everyday life, magnetic fields can be
most obviously observed through permanent magnets.
1.1 M EASUREMENT
Magnetic fields can be measured through the Hall Effect. This produces a voltage difference
across an electrical conductor (such as a metallic wire), transverse to an electric current in
the conductor and a magnetic field perpendicular to the current. [2] Simply, this effect can
be exploited with a coil, and used to spin a needle indicating relative magnetic field strength.
Many modern magnetic field sensors still exploit this effect, but a variety of more complicated
methods exist.
1.2 T YPES OF S ENSORS
As magnetic fields have a strength and direction, absolute and vector magnetometers exist. Specific magnetometers for applications such as measurement of the Earth’s magnetic
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Figure 1.1: A diagram explaining the Hall Effect, used as the basis of many modern magnetic
field sensors. [5]
field also exist (this would specify direction in terms of declination). Modern magnetometers
specify several practical specifications, which include:
• Sample rate. The number of readings per second.
• Bandwidth. How well a magnetometer tracks rapid magnetic field changes.
• Resolution. The smallest change in the magnetic field the magnetometer can resolve.
• Absolute error. The variance expected from each result.
• Drift. The change in absolute error over time.
1.3 C OST AND S OURCES
Magnetometers have been miniaturised to the extent that they can be incorperated into integrated circuits at low cost. As such, they are commonly found included in modern smartphones. Sensor units utilising the hall effect can be found online and locally for as little as a
few dollars. [3] [4]
1.4 A PPLICATIONS
Given the pervasive and fundamental nature of magnetic fields, magnetometers have a diverse range of uses. They can be used to locate submarines, hazards for tunnel boring machines and in coal mines, unexploded ordnance (mine-sweeper), and mineral deposits and
geological structures. They can also be used in heart-beat monitors, weapons positioning,
weather prediction, radio wave propagation and astrophysics. Magnetometers are deployed
in common smartphones to act as, among other things, compasses. [6]
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1.5 F URTHER R EADING
For an excellent and simple explanation of the Hall Effect, see [5].
R EFERENCES
[1] Wikipedia,
Magnetometer — Wikipedia,
The Free Encyclopedia,
2014,
http://en.wikipedia.org/w/index.php?title=Magnetometer&oldid=619400422, [Online;
accessed 4-August-2014]
[2] Wikipedia,
Hall effect — Wikipedia,
The Free Encyclopedia,
2014,
http://en.wikipedia.org/w/index.php?title=Hall_effect&oldid=609525092,
[Online;
accessed 4-August-2014]
[3] Jaycar
Electronics,
UGN3503UA
Hall
Effect
Sensor,
2014,
http://www.jaycar.com.au/productView.asp?ID=ZD1902&form=CAT2&SUBCATID=977#1,
[Online; accessed 4-August-2014]
[4] Deal
Extreme,
KY024
Magnetic
Detecting
Sensor
Module,
http://www.dx.com/p/ky024-magnetic-detecting-sensor-module-red-blue232563#.U9-mHPmSys0, [Online; accessed 4-August-2014]
2014,
[5] Hyperphysics,
Hall
Effect,
2014,
http://hyperphysics.phyastr.gsu.edu/hbase/magnetic/hall.html, [Online; accessed 4-August-2014]
[6] NASA
Goddard
Space
Flight
Center:
Polar,
Wind
and
Geotail
site,
About
Electronic
Magnetometers
and
about
Smoking,
2007,
http://pwg.gsfc.nasa.gov/earthmag/magmeter.htm, [Online; accessed 4-August-2014]
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