  Broadband electromagnetic transparency phenomenon is realized with a
well-designed graded-permittivity sphere, which has an extremely low scattering
cross section over a wide frequency range, based on the generalized Mie
scattering theory and numerical simulation in full-wave condition. The dynamic
polarization cancellation is revealed by studying the variation of the
polarization with respect to the frequency. Furthermore, a properly-designed
multi-shell sphere is also proposed and examined in order to reduce the
rigorous conditions for realizing the broadband transparency in experiments.
