A magnetoelastic microtransformer-based microstrain gauge

A magnetoelastic material is subject to a change in magnetic permeability when exposed to strain, a phenomenon known as the Villari effect (which is the inverse of Joule's magnetostriction). Using a magnetoelastic material appropriately in sensors assists measurement of mechanical forces, pressures, and elongations. One approach to use the Villari effect for strain gauge measurements is to build a microtransformer with a magnetostrictive core. An elongation of the substrate material causes the core to be strained, affecting the amount of coupling between the transformer's primary and secondary coil. Such a microtransformer is an attractive alternative to both classic metal strain gauges as well as piezoresistive devices (W. Heywang, Sensorik, Springer Verlag, Berlin, 1987).The microtransformer has been fabricated in thin film technology. While earlier investigations proved the feasibility of such an approach (L.H. Rissing, S.A. Zielke, H.H. Gatsen, Inductive microtransformer exploiting the magnetoelastic effect, IEEE Trans. Magn. 34 (4) (1998) 1378–1380), this paper describes the design and the performance of a microtransformer with an improved sensor layout, discusses experimental test results, and compares them to simulation results. Based on the measurement results and the mechanical properties of the test setup, a strain gauge factor k of 1500 was determined.