Working principle of the hottest GMR magnetic fiel

2022-08-01
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Working principle of giant magnetoresistance (GMR) magnetic field sensor

the magnetoresistance (GMR) effect is a magnetoresistance effect discovered in 1988. Because it is more than an order of magnitude larger than the traditional magnetoresistance effect, it is called giant magnetoresistance (GMR) for short

1. The principle of giant magnetoresistance (GMR) is shown in Figure 1

the giant magnetoresistance (GMR) effect results from the different spin states of the current carrying electrons and the different effects of the magnetic field, resulting in the change of the resistance value. This effect can only be observed in nano scale thin film structures. Given special structural design, this effect can also be adjusted to meet different performance needs

when antiferromagnetic coupling is applied (the applied magnetic field is 0), the conductive output characteristic is in the high resistance state. Resistance: r1/2

when the applied magnetic field makes the magnetic multilayer film in the saturated state (the magnetic moments of adjacent magnetic layers are distributed in parallel), while the conductive output characteristic of the resistance is in the low resistance state. Resistance: r2*r3/(r2+r3), r2>r1>r3

Figure 1. Use the two flow model to explain the mechanism of GMR

2 See Figure 2 for the principle of giant magnetoresistance (GMR) sensor

the giant magnetoresistance (GMR) sensor consists of four giant magnetoresistance (GMR) to form a Wheatstone bridge structure, which can reduce the impact of external environment on the output stability of the sensor and increase the sensitivity of the sensor. During operation, the "current input terminal" in the figure is connected with a space contraction and zigzag ~20v regulated voltage under 5V, and the "output terminal" outputs a voltage signal under the action of an external magnetic field

Figure 2 (1): principle of Wheatstone bridge in the application of magnetic field sensor

Figure 2 (2): changes of R1 and R2 in Wheatstone bridge under the action of external magnetic field

3 See Fig. 3 and table 1 for the performance of giant magnetoresistance (GMR) sensor

Figure 3 shows the performance curve of the giant magnetoresistance (GMR) sensor in the external field, indicating that the sensor has good linearity in the magnetic field range of ± 200oe

Figure 3: performance curve of giant magnetoresistance (GMR) under applied magnetic field

table I performance comparison of giant magnetoresistance (GMR) sensors of various companies

4 Product instructions

a As an active device, giant magnetoresistance (GMR) sensor must provide 5~20v DC power supply. Moreover, the stability of the power supply directly affects the test accuracy of the sensor, so it is required to provide it with a regulated power supply; Overvoltage power supply shall also be avoided in use

b . As a high-precision magnetic sensor, giant magnetoresistance (GMR) sensor also has certain requirements for the magnetic environment, and its model selection should be determined according to the magnetic field of the environment

c. the sensitivity of giant magnetoresistance (GMR) sensor to magnetic field is related to the direction. The sensitive axis marked on the outline structure is the most sensitive direction of the sensor to the magnetic field,

see Figure 4. When it is not parallel, the sensitivity decreases, and the relationship is

s θ= S0COS θ

where s θ Is the included angle between the magnetic field direction and the sensitive axis of the sensor θ S0 is the sensitivity when the magnetic field direction is parallel to the sensitive axis of the sensor

Fig. 4 outline structure and wiring diagram of giant magnetoresistance (GMR) sensor

d. when the output characteristic is low compared with the external magnetic reason, it is certain that its original quality field cannot be guaranteed to be even function, the sensor needs to be applied with a bias magnetic field when used for measurement. Ideally, the size of the bias magnetic field is 1/2 of the magnetic field within the range of the sensor to maintain linearity and avoid bumping. (end)

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