Effect of Grain Size on Magnetic Loss of Nanocrystalline Alloy Under High-Frequency Non-Sinusoidal Excitation

To investigate the effects of internal microstructure and high-frequency non-sinusoidal excitation on the magnetic loss of nanocrystalline alloy, a 3-D mesoscopic model based on G. Herzer’s theory of random anisotropy is developed. First, the ac test platform is used to measure the loss value of the nanocrystalline alloy under sinusoidal excitation, and then, the model is subjected to the same excitation to obtain its loss value. These values are compared to verify the model’s accuracy. Using the micromagnetic model provided by OOMMF software, we investigate the microscopic effect of grain size $d$ on the high-frequency magnetic loss $p_{v}$ of nanocrystalline alloys. Next, we apply non-sinusoidal alternating magnetic fields (square wave, trapezoidal wave, and triangular wave) to the model to explore $p_{v}$ under non-sinusoidal excitation. The results show that as the grain size $d$ of the nanocrystalline alloy increases, $p_{v}$ also increases. Additionally, when $d$ and the frequency $f$ are held constant, $p_{v}$ is greatest under triangular wave excitation, followed by trapezoidal wave excitation, and smallest under square wave excitation. This conclusion is due to the fact that the equivalent frequency $f_{\text {eq}}$ , which contains the rate of change of magnetic flux density ( $dB/dt)$ , can replace $f$ in the original Steinmetz formula when the excitation source is non-sinusoidal. Our calculations indicate that $f_{\text {eq}}$ is smaller under square wave excitation than under triangular wave excitation.