Load-bearing glass fabric/epoxy-MWCNT honeycomb sandwich composites optimized for broadband radar absorption via graded properties

Conventional honeycomb-based radar-absorbing structures (RAS) typically employ uniform material properties, which severely restrict broadband absorption when structural load-bearing capability is simultaneously required. To address this limitation, this study designed and optimized a multifunctional, gradient honeycomb sandwich RAS enabling concurrent control of electromagnetic and mechanical performance. The structure was fabricated using glass fabric/epoxy composites integrated with a spatially graded distribution of multi-walled carbon nanotubes (MWCNTs). The complex permittivity as a function of MWCNT loading was first evaluated, and the multi-layer honeycomb core configuration was optimized through flatwise compression and three-point bending tests according to ASTM C365 and ASTM C393 standards, while microwave absorption was verified experimentally. The optimized gradient composite demonstrated an outstanding effective absorption bandwidth exceeding 90% across a broad frequency range of 5.8-18 GHz (encompassing the C, X, and Ku bands). Concurrently, the mechanical characterization revealed significant structural enhancements, displaying an up to 57% increase in specific flexural modulus, 26% in specific flexural strength, 41% in specific compressive modulus, and 31% in specific compressive strength compared to conventional Nomex cores. To validate its practical relevance for stealth-oriented aerospace components, the structure was successfully implemented in a simulated leading edge of a NACA 64A210 airfoil, demonstrating a dramatic radar cross section (RCS) reduction under HH polarization at oblique incidence. These findings confirm that the proposed functionally graded MWCNT-honeycomb sandwich provides an exceptional, robust combination of load-bearing reliability and broadband stealth capability, making it a highly promising candidate for next-generation lightweight aerospace applications.