What's magnetic deviation angle?

Definition:

The magnetic deviation angle refers to the angular difference between the actual and the ideal magnetic dipole moments of a magnetized permanent magnet. It measures the deflection of the magnetization vector from its intended direction.

Causes of Magnetic Deviation Angle

1. Uneven Material Composition:

Inconsistent material distribution or crystalline structures within the magnet can result in irregular magnetization, causing a magnetic deviation.

2. Manufacturing Process Issues:

Imperfect application of a magnetic field during magnetization or suboptimal heat treatment processes can lead to a magnetic deviation angle.

3. External Magnetic Field Interference:

Nearby magnetic fields can alter the magnetization direction during the magnet’s manufacturing or application, contributing to magnetic deviation.

4. Temperature Changes:

Thermal fluctuations can affect the arrangement of magnetic domains, leading to deviations in the magnetization direction.

5. Mechanical Stress:

Shocks, mechanical stress, or vibrations may shift the orientations of magnetic domains, resulting in magnetic deviation.

Impact on Motors

1. Reduced Efficiency:

- A large magnetic deviation angle may prevent the magnet’s full utilization, lowering motor efficiency.

- The existence of magnetic deviation increases stray magnetic fields and leads to magnetic flux leakage, reducing the effective utilization of the magnetic field.

2. Speed and Torque Issues:

- Excessive deviation may misalign the rotor and stator magnetic fields, resulting in speed inconsistencies and failure to meet design specifications.

- Torque output can be affected, causing the motor to underperform within its designed torque range.

3. Increased Noise and Vibration:

- Larger magnetic deviation angles exacerbate motor noise and vibration due to the formation of asymmetric magnetic fields.

- These vibrations can impact smooth motor operation and shorten its service life.

4. Cogging Torque Problems:

- Magnetic deviation increases cogging torque, causing torque fluctuations during motor operation.

- Even with design optimizations like segmented skewed poles, severe magnetic deflection can undermine these improvements.

Impact on Sensors

1. Reduced Accuracy:

- Excessive magnetic deviation may lead to misalignment of the sensor with the magnetic field, reducing measurement accuracy.

- For instance, in magnetic angle sensors, large deviations can cause significant angle measurement errors.

2. Limited Sensing Range:

- Magnetic deviation can restrict the sensor’s ability to sense magnetic fields within its designed range.

- In high-precision magnetic angle sensors, deviations beyond ±3° can impair sensor performance.

3. Increased System Error:

- Misalignment between the sensor and the magnetic field due to magnetic deviation increases system nonlinearity errors (INL).

- For example, MPS’s MA600 magnetic angle sensor can reduce INL to 0.1° after user calibration, but excessive magnetic deviation can render calibration ineffective.

Recommendations for Mitigation

1. Material Optimization:

- Use high-quality, homogeneous materials to ensure consistent magnetization.

2. Process Control:

- Optimize magnetic field application during magnetization and maintain stringent heat treatment controls.

3. Environmental Protection:

- Shield magnets from external magnetic fields during manufacturing and application.

4. Temperature Management:

- Maintain stable operating temperatures to reduce domain rearrangement.

5. Mechanical Protection:

- Minimize exposure to mechanical stress, shock, and vibration.

By addressing these factors, manufacturers can reduce the magnetic deviation angle, thereby improving motor performance and sensor accuracy.