Electromagnetically induced torque on a large ring in the microwave range

Phys Rev Lett. 2014 Feb 7;112(5):053902. doi: 10.1103/PhysRevLett.112.053902. Epub 2014 Feb 5.


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.