Evaluation of magnetic flux density change for vibration energy harvesting: Comparison between direct and indirect measurements

The evaluation of magnetic-flux-density
$\Delta B$
due to the inverse magnetostrictive effect is important to develop superior inverse magnetostrictive materials for the application to vibration energy harvesting. In this study, the
$\Delta B$
value of an
$\text{Fe}-70$
at.%Co alloy was directly measured by applying dynamic stresses
$\Delta\sigma$
under constant magnetic fields. The
$\Delta B$
value in
$\Delta\sigma=160$
MPa increased with increasing magnetic fields and showed a maximum. The maximum value of
$\Delta B$
was approximately 0.35 T. This value is about 19% less than that evaluated indirectly from magnetization curves under constant stresses. Consequently, the
$\Delta B$
values obtained by the direct measurement indicate different behaviors from that obtained by the indirect measurement.