Theory and Implementation of Scattering-Dark-State Particles at Microwave Frequencies

Recently, a special scattering phenomenon due to nanostructured metallic-dielectric particles was reported. With the plasmonic dispersion of metals at optical frequencies, these nanoparticles can exhibit a 'scattering dark state,' showing a theoretically zero Rayleigh scattering. In this paper, aiming to implement such particles at microwave frequencies, we explain this scattering state using antenna theory. The analytical result shows that when the distance between two short dipoles approaches zero, their far-field radiations can be mutually canceled at the frequency where the derived condition is satisfied. Furthermore, simulation and experiments are performed to verify that either a single particle or a random collection of such particles could have omnidirectional invisibility. The derived theory also provides a new understanding to conventional microwave structures such as frequency-selective surfaces. Our method can be applied to a broad spectrum from radio frequency to optical regime, and can potentially inspire new applications such as perfect antenna radomes.