Micro-Doppler signatures of subwavelength nonrigid bodies in motion

Motion signatures of nonstationary electromagnetic bodies are imprinted in their scattering spectrum. While the Doppler frequency shift holds information about the velocity of its center of mass, internal degrees of freedom in a nonrigid body, such as rotation and vibration, introduce nontrivial spectral distortions, termed micro-Doppler signatures. Contemporary analytic characterization of such signatures typically neglects subwavelength electromagnetic coupling, which can dominate the scattering signatures of motion. To address this overlooked scattering regime, a theory of moving coupled dipoles is used to model a moving nonrigid body. The method is verified experimentally in the microwave regime, demonstrating remote sensing of subwavelength information. The method can be useful for analyzing and characterizing effects that frequently emerge in radar science, healthcare monitoring, optical manipulation of particles, and many other applications, where remote sensing and classification of motion are important.