Design and experimental validation of a mechanically tunable broadband electromagnetic absorber with a composite web core sandwich structure

초록

In this study, we propose a mechanically active frequency-tunable electromagnetic (EM) absorber prototype based on a web core sandwich composite. The proposed frequency-tunable active radar absorbing structure (RAS) controls its resonance behavior by mechanically adjusting the spacing of the internal perfect electric conductor (PEC) layer, thereby modifying the internal GAP and resonance condition without electrical biasing or intrinsic material-state modulation. This approach enables mechanically reconfigurable Salisbury screen absorption without complex bias circuits or active electronic components. Full-wave simulations and free-space measurements were conducted under both TM- and TE- polarization modes over the measurable frequency range of 5.8-18.0 GHz. The prototype was experimentally evaluated at discrete GAP positions from 1 to 10 mm. The TM-mode results were used as the primary quantitative validation case, showing GAP-dependent frequency tuning with experimental peak return losses ranging from -27.0 to -43.9 dB within the measurable range. The TE-mode measurements also showed GAP-dependent changes in absorption performance, although larger discrepancies between the simulated and experimental results were observed than in the TM-mode. Radar cross section (RCS) simulations predicted an average RCS reduction of 6.87 dB over 2-18 GHz relative to a PEC reference under normal-incidence VV polarization. The RCS itself was not experimentally measured, and no experimental return loss data were available over 2-5.8 GHz because of the lower-frequency limit of the measurement system. Furthermore, the web core sandwich structure exhibited an ultimate compressive strength of 225.7 MPa. The web core specimens exhibited material failure without skin-core interfacial debonding, whereas facesheet buckling was observed in the aluminum and Nomex honeycomb core sandwich structures. These results demonstrate that the proposed mechanically active RAS prototype integrates frequency-tunable EM wave absorption and mechanical robustness in a structurally simple sandwich configuration, showing potential for mechanically reconfigurable stealth structures.

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