The influence of low-level pre-stressing on resonant magnetoelectric coupling in Terfenol-D/PZT/Terfenol-D laminated composite structure

The resonant magnetoelectric coupling behavior in a Terfenol-D/PZT/ Terfenol-D laminated composite structure is experimentally studied with specific interest in the dependence on the pre-applied low-level mechanical stress up to 1.25 MPa. A laminated composite consisting of two Terfenol-D plates and one transversely polarized sandwiched-in PZT plate is fabricated in lab followed by pre-stressing along the direction of length, width, and thickness, respectively. It is observed that resonant magnetoelectric coupling develops in such pre-stressed composite when magnetically excited in each of the orthogonal directions, and the longitudinal mode of principle vibration can be confirmed. The action of pre-stresses generally elevates the frequency of resonance through the ΔE effect in Terfenol-D. In the meanwhile, the increased pre-stress lowers the value of the resonance magnetoelectric coefficient. This is partly attributed to the decrease of the effective quality factor of the structure along the increase of pre-stress, and partly attributed to the piezomagnetic coefficient of Terfenol-D, which either decreases or remains constant depending on the magnetizing state. In addition to the resonant behaviors, the tunability of the magnetoelectric coefficient of the pre-stressed structure is examined at fixed excitation frequency. For the structure excited in the length or width direction, the magnetoelectric coupling can reach the maximum at an optimal bias field. When excited in thickness, however, the magnetoelectric coupling becomes very weak, and the value of the coefficient increases monotonically with the pre-stresses. The increase of the pre-stress causes degradation of the maximum magnetoelectric coefficient for the structure when excited in length or width direction. This observation can be explained via the upshift of the resonance frequency of the structure caused by increased pre-stresses. Alternatively, it can be viewed as the consequence of the change in the maximum piezomagnetic coefficient of Terfenol-D, which is observed to decrease upon the increase of pre-stresses.