Most magnetic sensor systems consist of a magnetic field sensor that
measures the magnetic field in one or more directions and a magnetic
element that creates the magnetic field. Different kind of stimulus
changes the distance or the orientation of the magnetic element with
respect to the magnetic field sensor or even the magnetic properties of
the material in the magnetic element can change for a specific stimuli
which can be detected by the sensor. Thus, with a magnetic sensor system
it is possible to detect all kinds of parameters for instance distance,
orientation or even different kind of molecules in a liquid.
In other cases a magnetic field sensor can detect the magnetic
orientation in the magnetic element (which can be used to store data as
zeros and ones) positioned on a hard disk in a computer or in other types
of information carrier media. The magnetic field sensor can either be a
sensitive and low noise ordinary magnetoresistive sensor or a giant
magnetoresistance (GMR) sensor, a Hall sensor (to be used in a wider
field range) or just a coil wounded with copper windings (to be used at
higher frequencies since its sensitivity increases linearly with the
frequency).
Motion and position detection
The classic magnetic sensor system for position and orientation detection
is constructed as follows. Around a permanent magnet of, for instance an
NdFeB alloy (which is the strongest permanent magnet that it is possible
to purchase today), there lies a magnetic field. The strength and
direction of this magnetic field depends on the distance and direction to
the permanent (and also on the dimension and geometry of the magnet) in a
complex way. However, for small changes in direction and orientation the
strength is more or less linear to the changes in both distance or
changes in orientation. Together with a sufficiently sensitive magnetic
field sensor (that can measure the magnetic field strength in one or more
orthogonal directions) it can be used to measure changes in position down
to a few micrometers up to several millimeters and angle changes down to
a few milliradians up to a full rotation of an object. This kind of
sensor system can be designed for many application areas where
measurement changes in distance or orientation between two or more
objects is required. The complete sensor system is highly cost effective
in many applications. It can also be used in harsh environments (for
instance in high temperature conditions).
Recently it was reported that Adidas had used a magnetic detection
technique in their newly developed sport shoes in order to first measure
the compression of the sole of the shoe allowing the shoe to thereafter
automatically adjust the damping in the sole. Using sensitive magnetic
sensor systems it is also possible to detect the approach, speed and even
identification of objects manufactured with magnetic materials, for
instance vehicles.