Thermal Demagnetization Characteristics of NdFeB Used in Eddy Current Dampers

With continuously improving NdFeB magnetic properties, eddy current dampers using NdFeB materials as energy sources can be used in places with high energy consumption densities. However, the magnetic properties of NdFeB are greatly threatened by the increase in temperature, and the demagnetization process of NdFeB remains unclear. To comprehend demagnetization due to temperature increases in the working environment, this study reproduces the microscopic demagnetization process of NdFeB under high temperatures using the micromagnetic numerical simulation method. The demagnetization mechanism of NdFeB at different temperatures is analyzed using micromagnetic calculations, and the hysteresis phenomenon of NdFeB is explained accordingly. To quantify the demagnetization phenomenon of NdFeB in engineering practice, it is crucial to mathematically express its demagnetization behavior at different temperatures. We used the Jiles–Atherton (J–A) model, frequently used in ferromagnetic materials, to describe the demagnetization process. Next, a dynamic hysteresis experiment of NdFeB is conducted to validate the accuracy of the J– A model in expressing the magnetic properties. Finally, considering the artillery launch as a typical engineering case, the demagnetization and resistance drop calculation of the eddy current damper due to the heating of the permanent magnet during the launch process is performed. Results imply that under the worst working conditions, the maximum demagnetization amount of NdFeB is 0.351 T, and the maximum recoil displacement of the damper is 1,108 mm, theoretically supporting the design of the eddy current damper.