The rapid development of communication technologies has intensified electromagnetic pollution, creating an urgent demand for high-performance microwave absorbers. Herein, Fe@CNTs composites were synthesized via molten salt electrochemical reduction using CO₂ as the carbon source in a Na₂CO₃–K₂CO₃–CaCO₃ electrolyte. The microstructure, electromagnetic parameters, and microwave absorption performance were systematically investigated. The as-prepared sample exhibits an effective absorption bandwidth of 5.1 GHz at a thin thickness of 1.7 mm, surpassing most reported CNTs-based absorbers. Furthermore, a trapezoidal pyramid metastructure was designed to further broaden the bandwidth; the optimized metastructure achieves full-band absorption covering 2–18 GHz at a total thickness of 16.4 mm, representing a three-fold bandwidth enhancement over the planar configuration. This work provides a green, scalable synthesis route and an effective structural engineering strategy for ultra-broadband microwave absorption .

Designing highly reliable and practical microwave absorbers is one of the most important research directions in the microwave absorbing field. Many absorbents suffer from concentration-sensitivity and environmental-sensitivity dilemmas in practical applications. Here, sea urchin-like aggregates of MnO₂ nanotubes were synthesized by a simple hydrothermal method, which exhibit an outstanding impedance matching characteristic. The composites based on sea urchin-like aggregates of MnO₂ nanotubes show excellent microwave absorption performance in a wide concentration domain from 20 wt.% to 70 wt.%, corresponding to electrical conductivities from 1.86 × 10⁻⁷ to 1.85 × 10⁻⁵ S/m. Such a wide concentration range of absorbent for excellent microwave absorption is mainly attributed to the beneficial impedance matching properties of sea urchin-like aggregates of hollow nanotubes. A competitive absorption bandwidth of 3.36 GHz is achieved at 1 mm thickness, which can be broadened to 13.4 GHz by structural design. This work shows a new scheme for designing reliable and practical microwave absorbers benefit from the wide absorbent concentration domain.