Electromagnetic scattering in accelerating reference frames inspires avariety of phenomena, requiring employment of general relativity for theirdescription. While the quasi-stationary field analysis could be applied toslowly-accelerating bodies as a first-order approximation, the scatteringproblem remains fundamentally nonlinear in boundary conditions, giving rise tomultiple frequency generation (micro-Doppler shifts). Here a frequency comb,generated by an axially rotating subwavelength (cm-range) wire and split ringresonator (SRR), is analyzed theoretically and observed experimentally byilluminating the system with a 2GHz carrier wave. Highly accurate lock indetection scheme enables factorization of the carrier and observation of morethan ten peaks in a comb. The Hallen integral equation is employed for derivingthe currents induced on the scatterer at rest and a set of coordinatetransformations, connecting laboratory and rotating frames, is applied in orderto predict the spectral positions and amplitudes of the frequency comb peaks.Unique spectral signature of micro-Doppler shifts could enable resolving aninternal structure of the scatterers and mapping their accelerations in space,which is valuable for a variety of applications spanning from targetsidentification to stellar radiometry.
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