Electromagnetic scattering from moving bodies, being inherentlytime-dependent phenomenon, gives rise to a generation of new frequencies, whichcould characterize the motion. While a standard linear path leads to a constantDoppler shift, accelerating scatterers could generate a micro-Doppler frequencycomb. Here, a spectra produced by rotating objects, was studied and observed ina bi-static lock in detection scheme. Internal geometry of a scatterer wasshown to determine the spectra, while the degree of structural asymmetry wassuggested to be identified via signatures in the micro-Doppler comb. Inparticular, hybrid magneto-electric particles, showing an ultimate degree ofasymmetry in forward and backward scattering directions were investigated. Itwas shown that the comb in the backward direction has signatures at thefundamental rotation frequency and its odd harmonics, while in the forwardscattered field has the prevailing peak at the doubled frequency and itsmultiples. Additional features in the comb were shown to be affected by thedimensions of the particle and strength of magneto-electric coupling.Experimental verification was performed with a printed circuit board antenna,based on a wire and a split ring, while the structure was illuminated with at2GHz carrier frequency. Detailed analysis of micro-Doppler combs enables remotedetection of asymmetric features of distant objects and could find use in aspan of applications, including stellar radiometry and radio identification.
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