Past exam of the materials science course of the University of Cambridge / 2018 / Paper 1 / 2 / c / ii / Solution

Reversing a saturating longitudinal field gives approximately the same strain and the same voltage polarity relative to the original unmagnetized reference. In the isotropic orientational model,It is unchanged under $\mathbf{m}\to -\mathbf{m}$. Both positive and negative longitudinal saturation therefore contract the negative-magnetostriction nickel in the same axial direction. The resulting stress on the piezoelectric layer has the same sign.

During field reversal there can be a hysteretic transient as domains reorganize, and finite circuit leakage can alter the measured waveform. Those effects do not turn the saturated strain law into a response odd in the field.