The frequency dependence of eddy current losses in Terfenol-D

Abstract

The frequency response of the magnitude and phase of the dynamic relative permeability of Terfenol-D (Tb0.27Dy0.73Fe2) has been measured for low drive fields (a few hundred A m−1 rms) and the energy loss per cycle determined. The data shows that when eddy current shielding is not significant, the frequency dependence of the magnitude of this energy loss follows that calculated from classical eddy current theory, suggesting that there is negligible anomalous loss. The permeability, along with the dynamic strain coefficient, is observed to possess a flat response with frequency up to the value at which eddy current shielding of the sample core is expected to be significant. However, the ratio of the dynamic strain coefficient to the dynamic susceptibility (d/χ) remains independent of drive frequency, suggesting that the magnetization processes do not change. Measurements using high drive fields show that at 5 kA m−1 rms the frequency dependence of the loss is still in good agreement with classical eddy current theory. This data also shows that the loss angle is identical to that measured at low drive fields, indicating that the eddy current losses scale as the square of the drive field.