<Geomagnetic Sensor>
What is a geomagnetic sensor?
Earth’s magnetic field is also known as the geomagnetic field.
Geomagnetic sensors are sensors that detect the magnetic field of
the Earth, and are commonly referred to as electronic compasses.
Geomagnetic sensors can determine direction by detecting the
geomagnetic field.
Geomagnetic field surrounding the Earth

Geomagnetic sensors include 2-axis types (X and Y) and 3-axis models
with a Z axis that measures the magnetic force in that direction.
For simple compasses that do not need to consider the slope
(inclination), only the X and Y axes are used. However, when tilting
the compass it is necessary to correct it in the proper direction by
combining the values of the 3 axes from the geomagnetic sensor with
an accelerometer.
The below figure shows the distribution chart of the X and Y values
when the geomagnetic sensor is rotated horizontally.

If the geomagnetic sensor is rotated horizontally, in the ideal case
where there are no effects from the surrounding magnetic field, the
center of the circle of the output distribution map becomes zero.
However, since the center shifts due to the influence of the ambient
magnetic field, it is necessary to make an adjustment to move the
center of the circle to zero.
The north that can be derived from a geomagnetic sensor is called
the magnetic north (which is slightly shifted from the north pole),
and the direction can be known by simply calculating the angle from
this magnetic north using the above formula.
Various types of magnetic sensors
A magnetic sensor is a sensor capable of measuring the magnitude
and direction of a magnetic field.
A variety of sensors exist depending on the purpose, but the
following are typical examples.
Detection Method | Hall | MR | MI |
---|---|---|---|
Configuration |
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Anti-Noise (Sensitivity) |
× | △ | ◎ |
Current Consumption | × | △ | ◎ |
Response Speed | × | △ | ◎ |
Hall Sensor
A sensor that measures the magnetic flux density using the Hall
effect and outputs a voltage proportional to the magnetic flux
density is called a Hall sensor.
It is easy to use and mainly adopted for contactless switch
applications such as open/close detection of doors and notebook
PCs.
MR Sensor
An MR (Magnetoresistive) sensor measures field strength through
changes in individual electrical resistors based on the magnetic
field.
This type of magnetic sensor is used quite frequently due to its
higher sensitivity and lower power consumption vs Hall sensors. In
addition to geomagnetic detection in e-compasses, MR sensors are
used for applications such as motor rotation and position
detection.
MI Sensor
An MI (Magneto-Impedance) sensor is a next-generation magnetic
sensor that takes advantage of the magneto-impedance effects of a
special amorphous wire.
It features more than 10,000 times the sensitivity of Hall
sensors, allowing measurement of minute variations in the
geomagnetic field with high accuracy.
It is ideal for applications requiring high sensitivity, such as
indoor positioning, metal foreign object detection, and
ultra-low-current azimuth detection (e-compass).