Four-band flexible metamaterial absorber based on multi-layer square metal ringsBin Lou, Haojie Ye, Yongxing Jin, Junling Han, Lengyuan Niu, Manna Gu and Ying TianEur. Phys. J. D, 80 2 (2026) 13DOI: https://doi.org/10.1140/epjd/s10053-026-01120-3