Magnetometers are scientific instruments that measure the strength and direction of magnetic fields, varying by location due to Earth's rock composition and solar particle interactions. Different types include scalar and vector magnetometers, with historical advancements beginning in 1833 by Carl Friedrich Gauss. Modern iterations, such as rotatable coil, Hall effect, and atomic magnetometers, offer various methods and sensitivities for detecting magnetic fields, including applications in space exploration.

1. Magnetometer
Space Instrumentation and
Observation (I)
2/24 2011

2. Magnetometer
• A magnetometer is a scientific instrument
used to measure the strength and/or direction
of the magnetic field. Magnetism varies from
place to place and differences in Earth's
magnetic field can be caused by the differing
nature of rocks and the interaction between
charged particles from the Sun and the
magnetosphere. Magnetometers are a
frequent component instrument on spacecraft
that explore planets.

3. Types
• Scalar magnetometers measure the total
strength of the magnetic field to which they
are subjected, and
• Vector magnetometers have the capability to
measure the component of the magnetic field
in a particular direction, relative to the spatial
orientation of the device.

4. Early magnetometers
• In 1833, Carl Friedrich Gauss, head of the
Geomagnetic Observatory in Göttingen,
published a paper on measurement of the Earth's
magnetic field. It described a new instrument
that Gauss called a "magnometer" (a term which
is still occasionally used instead of
magnetometer). It consisted of a permanent bar
magnet suspended horizontally from a gold fibre.
A magnetometer may also be called a gaussmeter.

6. Modern magnetometers
• Rotating coil magnetometer
• Hall effect magnetometer
• Proton precession magnetometer
• Gradiometer
• Fluxgate magnetometer
• Caesium vapor magnetometer
• Spin-exchange relaxation-free (SERF) atomic
magnetometers

7. Rotating coil magnetometer
• The magnetic field induces a sine wave in a
rotating coil. The amplitude of the signal is
proportional to the strength of the field,
provided it is uniform, and to the sine of the
angle between the rotation axis of the coil and
the field lines.

10. Hall effect magnetometer
• The most common magnetic sensing devices
are solid-state Hall effect sensors. These
sensors produce a voltage proportional to the
applied magnetic field and also sense polarity.

12. Proton precession magnetometer
• Proton precession magnetometers, also
known as proton magnetometers, measure
the resonance frequency of protons (hydrogen
nuclei) in the magnetic field to be measured,
due to nuclear magnetic resonance (NMR).
Because the precession frequency depends
only on atomic constants and the strength of
the ambient magnetic field, the accuracy of
this type of magnetometer is very good.

15. Gradiometer
• Magnetic gradiometers are pairs of magnetometers
with their sensors horizontally separated by a fixed
distance. The readings are subtracted in order to
measure the difference between the sensed
magnetic fields, which measures the field gradients
caused by magnetic anomalies. This is one way of
compensating both the variability in time of the
Earth's magnetic field and for other sources of
electromagnetic interference, allowing more
sensitive detection of anomalies.

17. Fluxgate magnetometer
• A fluxgate magnetometer consists of a small,
magnetically susceptible, core wrapped by
two coils of wire. An alternating electrical
current is passed through one coil, driving the
core through an alternating cycle of magnetic
saturation. This constantly changing field
induces an electrical current in the second coil,
and this output current is measured by a
detector.

20. Caesium vapor magnetometer
• A basic example of the workings of a
magnetometer may be given by discussing the
common optically pumped caesium vapor
magnetometer which is a highly sensitive
(300 fT/Hz0.5) and accurate device used in a
wide range of applications.

23. Spin-exchange relaxation-free (SERF)
atomic magnetometers
• At sufficiently high atomic density, extremely high
sensitivity can be achieved. Spin-exchange-
relaxation-free atomic magnetometers containing
potassium, caesium vapor operate similarly to the
caesium magnetometers described above yet can
reach sensitivities lower than 1 fT/Hz0.5.
• The SERF magnetometers only operate in small
magnetic fields. The Earth's field is about 50 µT.
SERF magnetometers operate in fields less than
0.5 µT.

25. Magnetometers in Taiwan

26. Hangshen Station
National Chung Cheng University
Nei-Cheng Station
Yuan-Shan Station
Wan-Fu Station
National Dang Hwa University
Fu-Li Station

27. Wan-Fu Station

28. Yuan-Shan Station

29. Nei-Cheng Station

30. National Dang Hwa University