Definition and Classification of Magnetic Sensor
Magnetic sensors are widely used in modern industry and electronics to sense the magnetic field strength to measure current, position, motion, direction, and other physical parameters. In the technical field of magneto resistive transducers, there are many different types of sensors for measuring magnetic field and other parameters. Commercially important ones, in order of technical advancement, include: Hall Effect, AMR (Anisotropic Magneto Resistance), GMR (Giant Magneto Resistance) and the latest TMR (Tunneling Magneto Resistance).
The Hall Effect is a magnetic sensor sensing element for which the applied magnetic field is typically amplified using magnetic flux concentrator to improve the sensitivity of the Hall output, thereby increasing the size and weight of the sensor. Hall Effect has large power consumption and poor non-linearity. The AMR has much higher sensitivity than the Hall Effect’s, but it has a narrow linear operating range. The AMR magnetic sensor needs to use a set/reset coil for their preset/reset operation. It results in increasing the complexity of their manufacturing process, while also increasing their size and power consumption. The GMR magnetic sensor sensitivity is higher than that of AMR’s, but its linear range is still low.
Recently, TMR (Tunnel Magneto Resistance) was introduced as a new type of magneto resistance sensor for industrial applications. They are constructed as a magnetic multilayer film material. TMR magnetic sensor exhibits a greater change in resistivity, as a function of applied magnetic field induction, than that of the previously developed magneto resistance technologies, AMR and GMR. The term MTJ (Magnetic Tunnel Junction) is used to refer to a TMR sensor.