On wave modulation by a rotating object

When a time harmonic electromagnetic wave is incident upon a rotating object which is not rotationally symmetric about the axis of rotation, modulation in the secondary waves generally will occur. Two scattering and reflection problems where, under certain conditions, no modulation occurs, are discussed. In the first case, a transverse electric (TE) or transverse magnetic (TM) wave is incident upon an object inside a circular waveguide. The object is rotating about the axis of the waveguide and has periodic characterisitcs in the azimuthal direction with period
2\pi/N
(
N
: an integer). In the second case, the waveguide is removed, and a linearly polarized plane wave is incident upon the object along its axis of rotation.