Optimization Design of Honeycomb Absorbing Structure and Its Application in Aircraft Inlet Stealth

The growing demand for stealth technology in military and aerospace applications has driven the development of advanced radar-absorbing structures. In particular, honeycomb absorbing structures (HASs) have shown promise due to their unique properties. In order to enhance the absorption characteristics of HASs and evaluate its application effect on aircraft, firstly, the mechanism of enhancing the electromagnetic (EM) absorption capacity of honeycomb structures by using a gradient design for the impregnation material is studied. Secondly, a multi-layer gradient honeycomb absorbing structure (MGHAS) with top skin and intermediate bonding layers is proposed. The influence of the type and arrangement of impregnation materials on reflectivity is analyzed to obtain design strategies that can enhance the absorption performance of the MGHAS. An improved particle swarm optimization (PSO) algorithm is proposed to optimize the EM absorption performance of the MGHAS. The optimized MGHAS achieves broadband absorption below −10 dB in a 2–18 GHz range, and the reflectivity even reaches −30 dB near 10 GHz. Finally, to solve the problem of electromagnetic scattering characteristics of periodic structures, such as HASs applied to electrically large targets, reflectivity is introduced into a shooting and bouncing ray method, which is a high-frequency algorithm used to analyze the electromagnetic scattering characteristics of the aircraft inlet. Based on this method, the reduction effect of the MGHAS on the radar cross section (RCS) of the aircraft inlet is explored. The results indicate that at the detection angle at 0° and detection frequency at 10 GHz, an aircraft inlet equipped with the MGHAS achieves a 26 dB reduction in the RCS compared with an aircraft inlet without stealth technologies and an 18 dB reduction compared with an inlet with coating-type absorbing material in TM mode. This study demonstrates that the proposed MGHAS effectively reduces the electromagnetic scattering intensity of the aircraft inlet and enhances the radar stealth performance of the aircraft.