Radiation beats and rotating systems

If a wave of powerW and of angular frequencyω, circularly polarized, is reflected by a polarization inverter device, this wave exertes a torque 2W/ω on the device itself. In this work a circularly polarized wave is reflected by a polarization inverter device that rotates with angular velocity ±Ω, so we observe that the reflected wave frequency is shifted by Δω=∓2Ω. The experiment is done with a circularly polarized wave (ω=2π·9000 MHz) in a cylindrical wave guide excited in theTE10 mode. The results are explained considering the work done by the device. Besides it is shown that if the experiment is done with a wave in theTEm0 mode the reflected wave frequency is shifted by Δω=∓2mΩ. From intuitive arguments we obtain that these considerations are valid for a plane wave too.