A simple, high sensitivity torquemeter

A simple torquemeter has been developed with a sensitivity exceeding 10 −13 Nm when using a 13-μm-diam glass fiber and a low-mass suspension. The maximum twist angle of the fiber is constrained by the choice of its diameter to ∼1°. This angle is measured using a light, mirror, and split silicon photodetector, and is proportional to the torque on a sample in a rotating dc magnetic field.