This paper reports a central spiral split-rectangular-shaped metamaterial absorber surrounded by a polarization-insensitive ring resonator for s-band applications. The rated absorption is 99.9% at 3.1 GHz when using a three-layer structure where the top and ground are made of copper and the center dielectric material is a commonly used FR-4 substrate. The central split gaps have an impact on the unit cell by increasing high absorption, and an adequate electric field is apparent in the outer split ring gap. At 3.1 GHz, the permittivity and permeability are negative and positive, respectively, so the proposed unit cell acts as an epsilon negative (ENG) metamaterial absorber. In a further analysis, Roger4450B was used as a substrate and obtained excellent absorption rates of 99.382%, 99.383%, 99.91%, and 95.17% at 1.44, 3.96, 4.205, and 5.025 GHz, respectively, in the S- and C-band regions. This unit cell acts as a single negative metamaterial (SNG) absorber at all resonance frequencies. The S₁₁ and S₂₁ parameters for FR-4 and Rogers4450B were simulated while keeping the polarization angle (θ and φ) at 15, 30, 45, 60, 75, and 90 degrees to measure, permittivity, permeability, reflective index, absorption, and reflection. The values of the reflective index are near zero. Near-zero reflective indexes (NZRI) are widely used in antenna gain propagation. The unit cell fabricated for the FR-4 substrate attained 99.9% absorption. S-band values in the range of (2–4) GHz can be applied for low-frequency radar detection.

This article presents a polarization-insensitive, negative indexed inverted U-shaped flexible metamaterial absorber based on a microstructure resonator for multi-band energy harvester application. The vertical inverted U-shaped joint and central split ring resonator together create significant resonance covering three consecutive L-, S-, and C-band absorption peaks for four resonance frequencies: 1.975 GHz with 99.99% absorption, 2.85 GHz with 99.28% absorption, 5.265 GHz with 96.79% absorption, and 5.5 GHz with 89.12% absorption. The design has a rare double negative metamaterial feature at 5.265 GHz, while a balanced geometrical appearance that is polarization insensitive for θ and φ improved the structure’s durability and tunability. Finite computer simulation technology was used to simulate and examine the mechanisms involved in absorption at 1— 6 GHz. Based on Rogers RO4350 B and copper, the structural design showed excellent absorption for 15° and 30° bends and 2 × 4, 4 × 8 arrays with an efficiency of 96.38% at an incidence angle of 30° in transverse magnetic mode, a 3x 3 array was developed for energy harvesting. For energy harvesting applications using array structure, the efficiency parameter is unnoted in most of the reported articles. Moreover, the array demonstrated polarization insensitivity for both transverse electric and transverse magnetic modes at angles of 0°, 30°, and 60°. The proposed quad-band absorber shows significant potential for energy harvesting applications.