Magnetostrictive bilayer sensor system for testing of rotating microdevices

The paper reports the practical application of novel, highly bending sensitive bilayer force sensors, ribbons of about 100 μm in thickness, which consist of a magnetostrictive layer and a non-magnetic counter layer. Bending yields stress in the magnetostrictive layer, the sensitivity being adjustable by the physical properties of the counter layer. Force signals are established on the basis of permeability changes using a simple electronic circuit. Extremely high sensitivities proved to yield effective applications for the detection of ultra-low values of torque M (order of 10^-6 Nm) as being typical for rotational microdevices. For this study, torque measurements were performed on commercially available micro-motors utilising the cable brake principle in combination with the bilayer force sensors. The rotational speed was measured by means of a laser tachometer. The dependence of torque on rotational speed was then evaluated. The compact and low cost bilayers proved to act as ultra-low-force sensors with highest sensitivity, enabling rapid and effective torque tests of micro-motors.