Sensing Dynamic Forces by Fe–Ga in Compression

Abstract

This paper concerns the sensing of dynamic force/stress by means of a measuring system based on the use of an Fe–Ga sample (Galfenol) coupled to a magnetic circuit. The study is focused on the measurement of the effective magnetic field, detected at the rod specimen surface, and its variation $\Delta \! H_{\mathrm {eff}}$ under time-dependent applied sinusoidal stress $\Delta \sigma $ , oscillating at frequencies between 5 and 20 Hz at different values of applied bias field $H_{\mathrm {bias}}$ (2.5 kA/m $\le H_{\mathrm {bias}} \le 27$ kA/m). For the considered frequency and $H_{\mathrm {bias}}$ range, the measured $\Delta \! H_{\mathrm {eff}}$ tends to linearly depend on $\Delta \sigma $ , in contrast with the corresponding induction variation behavior ( $\Delta \! B-\Delta \sigma $ ), where hysteresis effects appear. With $\Delta \sigma $ in the range of ±15 MPa, we obtain 0.06 MPa resolution in the determination of the alternating stress $\Delta \sigma $ , a result pointing to the effectiveness and sensitivity of this Galfenol-based method for detection and measurement of time-dependent stresses.