Eur. Phys. J. D (2016) 70: 172
https://doi.org/10.1140/epjd/e2016-70193-6

Regular Article

Mechanism of angular momentum transfer from microwaves to a copper ring

¹ Université Rennes 1, 35042 Rennes Cedex, France
² UMR CNRS 6164 IETR, Université Rennes 1, 35042 Rennes Cedex, France
³ UMR CNRS 6251 IPR, Université Rennes 1, 35042 Rennes Cedex, France
⁴ Swedish Institute of Space Physics, Ångström Laboratory, P.O. Box 537, 751 21 Uppsala, Sweden

^a e-mail: olivier.emile@univ-rennes1.fr

Received: 15 March 2016
Received in final form: 25 May 2016
Published online: 30 August 2016

Abstract

In the exchange of orbital angular momentum between an electromagnetic wave and a copper ring we examine the origin of the Angular Momentum. We then investigate the transfer mechanism between the microwave and the object, and compare it with other mechanisms. We evidence a transfer mechanism based on the reflection of the electromagnetic field on the copper ring. In particular, at a microscopic scale, we show that the electromagnetic field induces alternative electric currents in the ring, with a small drift. Although little, the resistivity of copper leads to a force that rotates the ring. The estimation of the torque, which is of the order of 10^-8 Nm, is in good agreement with the experimental measurements. We also show that the transfer of electromagnetic orbital angular momentum to objects could be a way to measure the orbital angular momentum carried by electromagnetic fields, and we discuss possible applications.