Electrodeposited Fe–Ga Alloy Films for Directly Coupled Noncontact Torque Sensing

Torque measurements are used in a number of controls applications, but indirect coupling, size, and the quality of commercially available sensor materials can limit their utility. Here, a compact magnetostrictive torque sensor is made by electrodeposition of Fe_1-xGa_x (0.1<;x<;0.4, aka Galfenol), onto Cu shafts using rotating cylinder electrodes (RCEs). The alloy composition is controlled by tuning the RCE rotation rate between 500 and 2000 RPM, while the electrode potential is varied from 1.15 to 1.20 V. Direct coupling of Fe_1-xGa_x to the shaft with the electrodeposition process enables magnetic anisotropy to be induced via shaft surface texturing, as seen by a 260% increase in susceptibility along a 400 grit texturing direction versus perpendicular to the texture and compared with the isotropic behavior of films deposited on polished shafts. Inverse magnetostriction-based torque sensing is demonstrated by measuring stray fields from Fe_1-xGa_x films as torque loads of 0-16.9 Nm were applied to the shaft. Films electrodeposited on circumferentially textured shafts had torque responses almost 1.5 times greater than films electrodeposited on longitudinally textured shafts and five times greater than films on polished shafts.