The preparation of flexible ultra‐thin microwave absorption composite films for practical application is a known challenge. In this work, we use polydimethylsiloxane as the frame, extra conducting electric carbon black and carbonyl iron powder as absorbents. The microwave absorption performances of composite films can be well adjusted by changing the mass ratio of extra conducting electric carbon black and carbonyl iron powder. Meanwhile, the maximum reflection loss can reach −50.53 dB with a thickness of 1.63 mm, while the effective absorption bandwidth can achieve 4.80 GHz at a 1.48 mm thickness. The excellent microwave absorption performance can be attributed to the synergistic effect of good impedance matching, magnetic loss, dielectric loss and conduction loss. Importantly, the preparation of this ultra‐thin composite film explores the application of polydimethylsiloxane as a flexible framework material in microwave absorption field.
For electromagnetic windows (EWs), although the in-band transmission is satisfactory, reflection always exists upon interfaces, which will lead to considerable in-band RCS especially for large-size EWs. Conventional manners of reducing the in-band RCS are focused on enhancing transmission, which are always limited by the unavoidable impedance mismatch on interfaces. To overcome this limit, in this paper, we propose to reduce the in-band RCS of EWs by simultaneously enhancing transmission and coding reflection using dimer metasurfaces. The dimer structure is composed of two unidentical meta-atoms patterned on the front and back surfaces of EW, respectively, which can enhance the transmission in the band of interests. More importantly, when the dimer structure is flipped, the transmission is unaffected due to reciprocity, whereas the reflection will be different. Therefore, by coding the reflection phase, the in-band backward reflection can be further reduced due to scattering cancellation. Proof-of-principle prototypes were designed, fabricated, and measured to verify this strategy. The experimental results are consistent with the simulation results, which proves the feasibility of this strategy. This work provides an alternative way of reducing the in-band RCS of EWs and may find practical applications in radome, lens and others.
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