Magnetostrictive bilayer sensor for micro torque measurements

The paper reports the practical application of novel, highly bending sensitive bilayer force sensors, 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 composition of the counter layer. 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. Torque measurements were performed on commercially available micro-motors utilizing 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.