Electromagnetically Induced Torque on a Large Ring in the Microwave Range

We report on the exchange of orbital angular momentum between an electromagnetic wave and a 30 cm diameter ring. Using a turnstile antenna in the GHz range, we induce a torque on a suspended copper strip of the order of 10^-8 N m. Rotations of a few degrees and accelerations up to 4×10^-4 ^∘/s² are observed. A linear dependence of the acceleration as a function of the applied power is found. There are many applications in the detection of angular momentum in electromagnetics, in acoustics, and also in the magnetization of nanostructures.