Frequency-dependent, dynamic sensing properties of polycrystalline Galfenol (Fe_81.6Ga_18.4)

This paper presents the first measurement of Galfenol's frequency-dependent strain and magnetic flux density responses to controlled dynamic stress, from which frequency-dependent, effective material properties relating these quantities are calculated. Solid and laminated Galfenol (Fe_81.6Ga_18.4) rods were excited by 2.88 MPa compressive stresses up to 1 kHz under constant field and constant current conditions. Due to magnetic diffusion cut-off frequencies of only 59.3 to 145.7 Hz, the dynamic properties of the solid rod are found to vary significantly; this illustrates the inaccuracy of frequency-independent dynamic properties calculated via linear piezomagnetic models from experimental responses to electrical excitation. Conversely, the sensing properties of the laminated rod exhibit a weak dependence on frequency over the measurement range (i.e., a cut-off >1 kHz). The data are used to validate an existing model for mechanically induced magnetic diffusion. Loss factors and magnetomechanical energy densities are also presented and discussed in terms of loss separation, magnetic diffusion, and energy conservation.