1.2 Magnetic Sensors

Various classifications for sensors have been made [36,40]. A magnetic sensor converts a magnetic field into an electrical signal. Two applications can be distinguished for the magnetic sensors. In direct applications the magnetic sensor is part of a magnetometer. Examples are the geomagnetic field measurements, the reading of magnetic data storage media, the identification of magnetic patterns in cards and banknotes, and the control of magnetic apparatus. In indirect applications the magnetic field is used as an intermediary carrier for detecting non-magnetic signals. Examples are potential-free current detection for overload protection, integrated watt-hour meters, and contactless linear or angular position, displacement, or velocity detection using a permanent magnet. These applications require the detection of magnetic fields in the micro- and millitesla range, which can be achieved by integrated semiconductor sensors.

In the case of solid-state magnetic sensors such as MAGFETs, the measurand is the magnetic induction $\mathbf{B}$

$$\mathbf{B} = \mu\mu_0\mathbf{H}.$$ (1.1)

$\mathbf{B}$ is the magnetic induction in Tesla units (Vs/m$^2$), $\mathbf{H}$ is the magnetic field vector, $\mu_0$ denotes the permeability of free space, and $\mu$ is the relative permeability. Silicon is a low-permeability material, that is, $\mu$ is approximately one.