Programmable gradient structures for tunable microwave absorption: a dual-nozzle 3D printing-driven design framework

• A novel design and fabrication framework for gradient multilayer structures were developed. • GMSs possess not only precisely customizable absorption properties but also enhanced performance. • Dual-nozzle printing technology allows for the integrated fabrication of GMSs with arbitrary gradients. • The effect of gradient patterns on the frequency shift behavior was investigated. This study proposes a novel design and fabrication framework for gradient multilayer structures (GMSs) to develop high-performance, customizable electromagnetic wave (EMW) absorbers. Dual-nozzle printing technology allows for the integrated fabrication of GMSs with arbitrary gradients by providing a method to first build AMMs (with diverse dielectric properties tuned by the stacking ratio of PA to PA@CCF) which were then used as building blocks for the final, programable gradient structures. Supported by heuristic optimization algorithms, this framework allows strategic design of gradient configurations to precisely customize absorption peak frequencies while improving absorption performance. Theoretical calculations and experimental measurements confirm that the resulting GMSs exhibit outstanding performance across different thicknesses. Reversing the dielectric property gradient of the GMSs from decreasing to increasing along the incident direction of EMW shifts the first-order absorption peak to higher frequencies, while the higher-order peaks show oscillatory behavior. GMSs achieve tunability by modifying the impedance matching upon the penetration of incident waves as well as adjusting the quarter-wavelength interference cancellation conditions. Enhanced absorption stems from optimized impedance gradients and extended propagation paths via interlayer reflections. This work establishes a versatile and scalable platform for on-demand electromagnetic absorption management, opening a new pathway for advanced tunable EMW absorbers.