How to evaluate the performance of Special Shaped NdFeB Magnet in a complex magnetic field environment?

1. Core challenges of complex magnetic field environment
Complex magnetic field environment usually has the characteristics of multi-directional alternation, strong gradient and temperature fluctuation. Taking the electric vehicle drive motor as an example, the magnet needs to withstand: ① alternating magnetic field interference of more than 1000 A/m; ② working temperature range of -40℃ to 180℃; ③ mechanical stress caused by 6-axis vibration. Due to the geometric asymmetry, the magnetic domain distribution of Special Shaped NdFeB Magnet is easily disturbed by external fields, resulting in a magnetic moment deflection angle of 2-3 times that of conventional magnets.
2. Three-dimensional magnetic performance evaluation system
Material intrinsic analysis
The VSM vibrating sample magnetometer is used to measure Br (remanence), Hcj (coercive force) and (BH)max (maximum magnetic energy product). The anisotropy index (δ=Hk/Hcj) is observed in particular. When δ<0.9, it indicates that the magnet's anti-demagnetization ability is significantly reduced.
Multi-physics coupling simulation
The three-dimensional finite element model is established through COMSOL Multiphysics, which must include:
Bidirectional coupling of temperature field and static magnetic field (temperature coefficient αBr≈-0.12%/℃)
Dynamic eddy current loss calculation (eddy current density at the edge of special-shaped magnets can reach 4 times that of the central area)
Stress-magnetization coupling module (piezomagnetic coefficient λ≈3×10^-6 MPa^-1)
Dynamic test verification
The test platform is built in accordance with the IEC 60404-5 standard. The key indicators include:
Dynamic hysteresis loss (should be <15 at 100Hz) mW/cm³)
Magnetic field uniformity deviation (recommended to be controlled within ±5%)
Temperature cycle stability (Br attenuation should be <3% after 1000 cycles of -40-150℃)
III. Typical case analysis
The key performance of the C-type NdFeB magnet used in a medical CT device has been improved after optimization:
The δ value has been increased from 0.82 to 0.93 through the gradient annealing process
The arc magnetic circuit design reduces the stray field by 42%
The surface AlCrN coating reduces the high-temperature demagnetization rate by 67%