Efficient Gradient‐Enhanced SLSQP Optimization Design of Ultra‐Thin Broadband Honeycomb‐FSS Structure

ABSTRACT Honeycomb structures show promising applications across various fields due to their excellent electromagnetic absorption and mechanical capabilities, though challenges remain in broadband performance and design efficiency. This paper introduces frequency selective surfaces (FSS) to effectively modulate the impedance of honeycomb structures and proposes a gradient‐driven optimization framework for multilayer honeycomb‐FSS composite absorber (MHFCA). We derive the differentiable gradient function for absorption performance and integrate it with the sequential least squares quadratic programming (SLSQP) algorithm to explore multi‐dimensional design spaces better. Compared to common metaheuristic algorithms, the proposed framework reaches convergence in only 52.8% of the iteration time required by particle swarm optimization for multilayer coupled structures, while maintaining comparable solution quality. We optimize different FSS patterns for MHFCA structures based on this optimization framework. Results show that the optimized single‐layer structure achieves a −10dB absorption bandwidth from 8.2 GHz to 18 GHz, while the optimized three‐layer structure extends the effective absorption bandwidth to 3.3–18 GHz (fractional bandwidth is 138.3%) with a total thickness of only 0.11λ L .