TMR (Tunneling Magneto Resistance) angle sensor is a high-precision sensor based on the tunneling magneto resistance effect, which is widely used in industrial control, automotive electronics, aerospace and other fields. Its working principle deeply combines the magnetic theory of physics and the principle of electronics, by measuring the change of resistance value to determine the direction and strength of the magnetic field, and then determine the angle information.
I. The basic principle of TMR effect
The TMR effect, or tunneling magnetoresistance effect, is a special phenomenon that occurs in magnetic tunnel junctions (MTJs), which consist of two ferromagnetic layers (fixed and free) separated by a non-magnetic insulating layer (barrier layer). When the insulating layer is thin enough (usually a few nanometers), electrons can cross the insulating layer from one ferromagnetic layer to the other under the effect of quantum tunneling. This tunneling process is extremely sensitive to the magnetization directions of the two ferromagnetic layers: when the magnetization directions of the two layers are parallel, the tunneling resistance is small; when the magnetization directions are antiparallel, the tunneling resistance is large. Therefore, by measuring the change of tunneling resistance, it can reflect the relative change of the magnetization direction of the two ferromagnetic layers.
II. Structure of TMR angle sensor
The TMR angle sensor usually consists of two parts: the TMR sensor chip and the permanent magnet. Among them, multiple MTJ structures are integrated inside the TMR sensor chip, and each MTJ structure contains a fixed layer, a barrier layer and a free layer. The magnetization direction of the fixed layer is fixed during the manufacturing process and does not change with the external magnetic field; the magnetization direction of the free layer is relatively flexible and can change with the external magnetic field. The permanent magnet is used to generate a stable magnetic field, and when the permanent magnet rotates, the direction of the magnetic field it generates will also change, thus affecting the magnetization direction of the free layer in the TMR sensor chip.
III. Working principle of TMR angle sensor
1. Influence of magnetic field on the free layer
When the permanent magnet rotates, the direction of the magnetic field it produces changes. This changed magnetic field will act on the free layer in the TMR sensor chip, causing the magnetization direction of the free layer to change accordingly. Since the magnetization direction of the free layer is directly related to the magnitude of the tunneling resistance, a change in the magnetization direction will result in a change in the tunneling resistance.
2. Relationship between resistance change and angle
In TMR angle sensors, multiple MTJ structures are usually arranged on the sensor chip according to a certain layout, and the resistance changes of these MTJ structures are converted into measurable electrical signals by circuit design. When the permanent magnet rotates, the change in the direction of the magnetic field leads to a change in the direction of the magnetization of the free layer, which in turn causes a change in the tunneling resistance. After these resistance changes are converted into electrical signals, the angle of rotation of the permanent magnet can be determined by further processing and analysis.
Specifically, TMR angle sensors typically employ circuit designs such as Wheatstone bridges to minimize the effects of external factors such as temperature on the measurement results. When the permanent magnet rotates, the MTJ structures at different locations on the sensor chip are subjected to magnetic fields of different directions and sizes, resulting in different changes in their resistance values. These changes in resistance values generate a differential signal in the Wheatstone bridge, the size of which is proportional to the rotation angle of the permanent magnet. By measuring the size of this differential signal, the angle of rotation of the permanent magnet can be determined.
3. Angle Measurement Range and Accuracy
TMR angle sensors usually have a wide measurement range and high measurement accuracy. Since the TMR effect is very sensitive to changes in the direction of the magnetic field, TMR angle sensors are able to realize accurate measurement of small angular changes. At the same time, due to the use of non-contact measurement, the TMR angle sensor avoids problems such as mechanical wear and contamination, and improves the stability and reliability of the measurement.
IV. Advantages and Applications of TMR Angle Sensor
1. Advantages
High accuracy: TMR angle sensors can realize the precise measurement of small angular changes, with high measurement accuracy.
High sensitivity: Because the TMR effect is very sensitive to changes in the direction of the magnetic field, so the TMR angle sensor has a high sensitivity.
Low power consumption: TMR angle sensors consume less power during operation, which is conducive to energy saving and environmental protection.
Low Noise: TMR angle sensors have a high signal-to-noise ratio and can accurately measure angle information in complex environments.
Low Temperature Drift: By adopting circuit design such as Wheatstone bridge, TMR angle sensor can reduce the influence of temperature and other external factors on the measurement results, and has low temperature drift.
2. Application
Industrial control: In industrial automated production lines, TMR angle sensors can be used to measure the rotation angle and position information of mechanical parts to realize precise control.
Automotive electronics: In the automotive industry, TMR angle sensors can be used to measure the rotation angle and position information of steering wheels, steering wheel shafts, wheels and other components, to improve the stability and safety of automobile driving.
Aerospace: In the aerospace field, TMR angle sensors can be used to measure the attitude, rudder deflection and other key parameters of the aircraft to ensure the safety and stability of the aircraft.
V. Conclusion
TMR angle sensor is a high-precision sensor based on the tunnel magnetoresistance effect, and its working principle determines the direction and strength of the magnetic field by measuring the change of the resistance value, and then determines the angle information. Due to its advantages of high accuracy, high sensitivity, low power consumption, low noise and low temperature drift, TMR angle sensors are widely used in industrial control, automotive electronics, aerospace and other fields. With the continuous development and progress of science and technology, TMR angle sensors will play an even more important role in the future.