Rotational Doppler Effect of Spinning Metasurface in Radar System

In this paper, we demonstrate through the use of a spinning polarization-independent metasurface, the ability to detect the rotational Doppler effect from a radar system. The proposed metasurface with ring shape unit cells is polarization independent and can generate an OAM beam by reflecting an arbitrary polarized incident wave. In our demonstration, a radar transmits a normal electromagnetic wave illuminating on the proposed spinning metasurface, the wave interacts with the proposed metasurface and returns as an OAM wave with rotational Doppler shift. As shown from spectrograms based on measured data, the frequency shift is determined by the angular velocity and OAM mode of the proposed metasurface, the measured spinning speed errors are less than 3.6%.