A Split-Ring Resonator-Loaded Honeycomb Sandwich Structure for Broadband Microwave Absorption

Split-ring resonators are excellent left-handed metamaterials for significant electromagnetic coupling behavior. In this work, a split-ring resonator prepared with Ni-doped zeolitic imidazolate framework-67/epoxy resin (ZIF-67/ER) was embedded in the top layer to optimize microwave absorption efficiency in the 2-4 GHz frequency band. The Ni-doped ZIF-67/epoxy resin served as the bottom layer to improve microwave absorption efficiency in the 4-8 GHz frequency band. Honeycomb with a conductive carbon black coating served as the middle layer to generate electromagnetic loss for the overall frequency band. Based on the composite structure integration technology, RL < -10 dB was realized under the oblique incidence of 0-70 degrees. Both simulation and experiments indicate that a split-ring resonator made of lossy material can be an effective strategy to broaden the effective absorption bandwidth and increase the corresponding structure's insensitivity to polarization and the incidence angle of microwave.