Bioinspired Frequency Selective Rasorber with Closely Spaced Bands

This paper introduces a novel frequency-selective rasorber inspired by the geometry of the Oxalis tetraphylla plant. The proposed design combines a metasurface and a frequency-selective surface (FSS), both featuring bioinspired geometrical patterns. Designed to operate at 1.6 GHz, 2.5 GHz, and 3.5 GHz, the structure was fabricated and experimentally validated. The measured resonance frequencies were closely spaced, with frequency ratios of 1.51 (between the first and second) and 1.41 (between the second and third). The FSS exhibited polarization independence and angular stability for oblique incidences until 30°. The final prototype demonstrated high absorption efficiencies of 98.66% at 1.65 GHz, 99.67% at 2.4 GHz, and 98.62% at 3.51 GHz, with absorption frequency ratios of 1.45 and 1.46 between successive bands. The rasorber showed excellent polarization stability, angular robustness, and strong performance across the S- and C-bands. Specifically, in the S-band (e.g., 1.65 GHz), the structure is suitable for satellite communications, GPS, and military systems, while in the C-band, it is ideal for Wi-Fi (2.4 GHz) and emerging 5G applications (3.51 GHz).