Design and fabrication of a strong absorption gradient multilayer honeycomb with wideband absorption

Achieving full-band (2–18 GHz) microwave absorption alongside structural load-bearing capacity remains a formidable challenge. Traditional honeycomb absorbers enhance absorption but often require increased thickness and weight, limiting their practical applicability. To address this, we propose a novel composite gradient honeycomb structure. A gradient in electromagnetic properties is engineered by strategically varying the carbon black (CB) content and distribution within the coating. This creates a continuous gradient in the electromagnetic properties, achieving excellent impedance matching within a wide frequency band. Guided by a CST Studio optimized and closed-loop design framework, we fabricated a 30 mm height sample that achieves a reflection loss (RL) of ≤−10 dB across 2.2–18 GHz. Compared to a uniform absorber, this gradient structure enables broadband absorption with reduced thickness. Critically, the key to the broadband absorption is a multi-scale synergistic mechanism: the gradient architecture prolongs wave propagation within the honeycomb cells and optimizes impedance characteristics while simultaneously enhancing interfacial polarization and conductive loss. This integrated structural-functional design provides a promising pathway for developing lightweight, high-strength, and broadband microwave-absorbing materials.