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Magnetic sensors are devices that convert various magnetic fields and their changing quantities into electrical signals for output. We can artificially set up a permanent magnet, the use of its magnetic field as a carrier of information, so that the magnetic sensor to undertake a set of detection, storage, conversion, reproduction and monitoring of various magnetic fields and magnetic fields in the task of information. In today's information society, magnetic sensors have become an indispensable cornerstone component of information technology and information industry. At present, people have developed a variety of physical, chemical and biological effects of magnetic sensors, and in scientific research, production and all aspects of social life has been widely used.

Classification and Introduction of Magnetic Sensors

Today, we will mainly introduce Hall elements, anisotropic magnetoresistive AMR elements, giant magnetoresistive GMR elements and tunneling magnetoresistive TMR elements, which are four kinds of magnetic sensors

Hall Sensors

Hall sensors, as the name suggests, are based on the Hall effect. Hall effect is the basic method of studying the properties of semiconductor materials, the Hall coefficient determined by Hall effect experiments, to be able to determine the conductive type of semiconductor materials, carrier concentration and carrier mobility and other important parameters.

Hall sensors are divided into linear Hall sensors and switching Hall sensors.

1. Linear-type Hall sensors are composed of Hall elements, linear amplifiers and emitter followers, and output analogue.

2. Switching Hall sensors consist of a voltage regulator, Hall element, differential amplifier, smith trigger and an output stage, which outputs a digital quantity.

According to the Hall effect with semiconductor materials made of components called Hall elements. It has the advantages of magnetic field sensitivity, simple structure, small size, wide frequency response, large output voltage variation and long service life. Therefore, it is widely used in the fields of measurement, automation, computer and information technology.

Anisotropic magnetoresistive AMR

Anisotropic magnetoresistive sensors, ditto, are made using the magnetoresistive effect.

In 1857, Thomson discovered the anisotropic magnetoresistive effect.

The anisotropic magnetoresistive effect (AMR) refers to the fact that when the external magnetic field is at a zero-degree angle to the direction of the built-in magnetic field of the magnet, the resistance does not change with the applied magnetic field; however, when the external magnetic field is at an angle to the built-in magnetic field of the magnet, the magnetisation vector inside the magnet is shifted, and the resistance of the film decreases.

AMR is good at sensing weak magnetic field measurements within the geomagnetic field, and is often made into rotational speed sensors, proximity switches, isolation switches, as well as compasses in navigation systems, computers, and other devices. As well as navigation systems in the compass, computer disk drives, a variety of magnetic card machines, rotary position sensing, drilling orientation.

Giant Magnetoresistor GMR

Giant magnetoresistance (GMR) is a phenomenon in which the electrical resistivity of a magnetic material changes dramatically in the presence of an external magnetic field compared to the absence of an external magnetic field. Giant magnetoresistance arises from a layered magnetic film structure, which consists of thin layers of ferromagnetic and non-ferromagnetic materials alternately laminated together. When the magnetic moments of the ferromagnetic layers are parallel to each other, the scattering of carriers with respect to spin is minimised and the resistance of the material is minimised. When the magnetic moments of the ferromagnetic layers are antiparallel, the spin-related scattering is the strongest, and the resistance of the material is the highest at this time.

Based on the giant magnetoresistance effect developed an extremely sensitive magnetic head, which can clearly read out the weaker magnetic signals and convert them into clear current changes, and the appearance of this head triggered the hard drive "high-capacity, miniaturised" revolution. At the same time, giant magnetoresistors can also be used in MRAM, angle or position sensors, current sensors, bio-detection, and military fields.

Tunneling Magnetoresistor TMR

TMR element is a new type of magneto-resistive effect sensor that has begun to be used industrially in recent years, which utilises the tunneling magneto-resistive effect of the magnetic multilayer film material to sense the magnetic field, and has a greater resistive rate of change than AMR elements and GMR elements.

At present, AMR sensors have long been used on a large scale, and GMR sensors are developing rapidly.
TMR sensing technology was first applied to hard disc drive readout heads, which dramatically increased the recording density of hard disc drives.
TMR combines the high sensitivity of AMR with the wide dynamic range of GMR, and thus, among all types of magnetic sensor technology, the TMR magnetic sensors have an unparalleled technical advantage. TMR magnetic sensors have an unrivalled technical advantage among all types of magnetic sensor technology. Therefore, TMR sensors can be widely used in industrial control, financial instruments, biomedical, consumer electronics, automotive field and so on.