Time-Varying Metasurfaces for Target Recognition

Time-varying metasurfaces are emerging technologies that revoke the fundamental physical bounds of linear time-invariant (LTI) systems and provide a new manipulating freedom of time in metasurfaces. In this paper, pseudorandom noise sequence time-varying metasurfaces are proposed to combine the properties of pseudo-random noise sequence and time-varying metasurfaces for target recognition. By covering the targets to be recognized with time-varying metasurfaces that are modulated by different pseudo-random noise sequences, the metasurfaces scatter the incident harmonic wave into a modulated wave with their time-varying information. Therefore, the detector with the foreknowledge of the pseudo-random noise sequence may recognize the target by performing cross-correlation between the reflected wave after downshifting and the modulation pseudo-random noise sequences. The proposed metasurface-based target recognition is demonstrated by a proposed 1-bit tunable metasurface. The experimental results show that it can detect the present and non-present metasurfaces successfully, hence demonstrating the proposed time-varying metasurface based target recognition.