Variable-Periodic Sequence Time-Modulated Metasurface-Enabled RFID Tags for Time–Frequency Signature Generation

In this article, a method based on variable-periodic sequence time-modulated metasurfaces is proposed to generate time–frequency signatures for radio frequency identification (RFID) tags, which address the critical challenges of jamming and target mobility in the identification of friend or foe (IFF) system. Unlike traditional spectral-based approaches, the proposed method introduces nonuniform temporal modulation to generate adaptive time–frequency signatures, enabling robust IFF under dynamic conditions. Through dynamic controlling of variable-periodic sequences, the harmonic of the modulating signal distributions is translated into distinguishable time–frequency features. This approach achieves three key advancements: 1) enhanced antijamming ability, leveraging the spectral scalability of time–frequency patterns to avoid the impact of jamming environment; 2) motion robustness, decoupling IFF features and Doppler shifts to ensure stable identification of moving targets; and 3) high data capacity, significantly expanding the encoding space compared to spectral-based designs. The experimental validation using a 1-bit metasurface prototype demonstrates that the proposed method can achieve distinguishable time–frequency characteristics through variable-period sequences. This work offers a scalable, low-cost solution for the next-generation IFF systems in cognitive electronic warfare.