Field dependence of magneto-mechanical damping in magnetostrictive material for magnetic field sensing

The magneto-mechanical damping (MMD) in Terfenol-D is investigated by measuring the resonance vibration spectra of Terfenol-D bar. It is observed that MMD in Terfenol-D strongly depends on DC magnetic field (H_dc), and the ratio of the maximum variation of MMD over H_dc to the MMD at zero bias field achieves ~255%. Taking advantage of this MMD dependence on H_dc, a coil-less DC magnetic field sensor is proposed by attaching a Terfenol-D layer to a piezoelectric micro-transformer. An analytical model for the composite micro-transformer is developed and validated. The results show that the transformer voltage gain is inversely proportional to its damping and therefore depends on H_dc. In addition, the sensor sensitivity can be controlled by changing the input voltage of the composite micro-transformer. Preliminary test results are presented as principle verification with a mesoscale Terfenol-D/Pb(Zr,Ti)O₃ composite transformer. The experimental results show that the magneto-electric sensitivity with respect to H_dc achieves ~5.54 mV/Oe under the excitation of an input voltage with magnitude of 0.5 V.