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Electromagnetic wave (EMW) pollution poses a tremendous effect on information security and human health. However, ordinary concrete structure incorporated by ferrite fiber lacks EMW absorption flexibility to form electromagnetic superstructures. 3D printing technology paves an effective way to facilitate the anisotropy of electromagnetic absorption capacity by generating directional effects on ferrite fiber. This research evaluates the influence of 3D-printed fiber-oriented superstructure on EMW absorption performance with an equivalent waveguide attenuator model. The microwave-absorbing cementitious composite (10% magnetite and 25% copper slag) was prepared to incorporate 0.5 wt% copper fibers (CF) and steel fibers (SF), respectively. Absorption elements in each group are prepared by laminar parallel printing, cross-printing, and zigzag printing. In addition, the EMW absorption capability (ranging from 2 GHz to 18 GHz) was investigated by the Naval Research Laboratory (NRL) equipment. The overall EMW absorption performance of the SF samples is superior to CF samples. The optimized order of the EMW absorption performance of CF-reinforced samples is determined as zigzag, parallel, and cross printing, while SF is parallel, cross, and zigzag printing methodology. Overall, the laminar parallel printed steel fiber element gave the best shot with a peak reflectivity of − 16.34 dB and an absorption bandwidth of 13.15 GHz. Meanwhile, SF-reinforced specimens all demonstrated absorption peaks around 8 GHz, while CF-incorporated samples' absorption peaks appeared at both 8 GHz and 12 GHz, offering multiple design and application choices according to engineering requirements. Finally, an equivalent attenuator model is suggested for illustrating the superimposed reinforcement, spatial impedance matching, and multiple scattering of dielectric properties. • The prominent fiber orientation effect induced by 3D printing facilitates the enhancement of EMW anisotropic properties. • Copper fibers with slender dimensions form abundant and flexible multi-size equivalent waveguide attenuator structures that promote vector superposition and interference effects, exhibiting RL peaks at both 7 GHz and 12 GHz. • The steel fiber-reinforced samples are superior to the fine copper fiber samples in terms of overall electromagnetic absorption performance. The steel fibers and the surrounding concrete exhibit various gradients in their ability to adsorb EMW, resulting in a completely absorbing superstructure. • The electromagnetic wave absorption mechanism of the equivalent waveguide attenuator model for the fiber-reinforced composite is analyzed in detail. [ABSTRACT FROM AUTHOR]

• EMW-absorbing composite containing 6 wt% copper powder and 25 wt% copper slag. • EMW superstructures using 3D-printed oriented copper fiber upon microwave reflectivity. • Equivalent waveguide attenuator model and mechanism is proposed. • The copper fiber-reinforced element through crossed printing is the optimized configuration. • The superstructure creates a −20.43 dB reflectivity peak with an 11.79 GHz bandwidth. Electromagnetic wave (EMW) pollution negatively impacts information, equipment security, and the human body. However, neither powder phase absorbent nor ferrite fiber using traditional casting methodology cannot form electromagnetic superstructure to flexibly enhance EMW absorbing capacity. Thereby, ferrite fiber absorbent in well-oriented manner by 3D printing can be a feasible solution in EMW absorption due to its structural EMW anisotropy property. In this study, the influence of EMW superstructures using 3D-printed oriented copper fiber upon microwave reflectivity is investigated, and an equivalent waveguide attenuator model is proposed. First, an EMW-absorbing composite containing 6 wt% copper powder and 25 wt% copper slag is prepared. In copper slag cementitious composite, copper fiber (CF) and steel fiber (SF) are incorporated at 0.5 wt% separately. In each group, EMW-absorbing elements are manufactured through casting, laminar parallel printing, and cross printing. The superstructure anisotropy and EMW absorption performance are investigated through a network analyzer. The cross superstructure is outstanding in low-frequency absorption, while the parallel superstructure demonstrates desirable reflectivity at a high-frequency range. The copper fiber-reinforced element produced through crossed printing is determined as the optimized configuration, reaching a −20.43 dB reflectivity peak with an 11.79 GHz bandwidth. Lastly, an equivalent waveguide attenuator model is proposed to explain the superposition enhancement of the dielectric property, space impedance matching, and multiple scattering. [ABSTRACT FROM AUTHOR]

• The industrial by-products, solid wastes, carbon materials are discussed. • The steel fiber and ferrite exhibit satisfied EMW absorbing mechanical resistance. • The resonance materials improve EMW absorbing capacity with inferior strength. • The multi-phase and multi-layer composites and macrostructure are prospective. • The combination of 3D printing and EMW absorbing brings advantages. The ever increasing electromagnetic energy and multiple reflections of electromagnetic wave (EMW) impair human health and information security. The EMW absorbing cementitious material paves an innovative way to improve EMW absorbing performance of concrete structures. This study will elaborate on the EMW absorbing mechanism including energy exhaustion and impedance matching. A comprehensive review on the raw absorbent cementitious materials and the relevant preparation methods to be integrated into EMW absorbing concrete. Two new theoretical models are proposed including optimization zone model and equivalent electromagnetic parameter model to improve the current transform line model. Subsequently, the measurement and evaluation methodologies for EMW absorbing performance of cementitious materials are summarized. The expected research topics and applications of EMW absorbing cementitious materials are suggested. Through this critical review on the research status of EMW absorbing concrete, suggestions for optimizing the performance and workability of cementitious material are made to promote large-scale 3D printing technology. [ABSTRACT FROM AUTHOR]

• Four nano-sized graded absorbents were explored. • The 5 wt% coupling agent and 10 wt% dispersant was validated for graded absorbent. • The double-layer structure was made using spraying and extruding methodology. • The EMW mechanism for the graded double-layer structure was firstly summarized. • Theoretical calculation optimized a 15 mm absorbing layer and 15 mm impedance layer. The ever-increasing electromagnetic wave (EMW) energy and its reflections may impair human health and information security. An ordinary EMW-absorbing structure usually exhibits limited EMW-reflecting capacity given its ungraded structure in both the micro and macro scales. In this study, four nano-sized graded absorbents are explored by wrapping carbonyl-iron powder with nano-sized silicon dioxide. The micro-scale wrapping effects are assessed via a scanning electron microscopy experiment to identify the best sample, including a 5 wt% coupling agent and a 10 wt% dispersant in CIP ethanol. The 10 mm thick concrete matching layer containing the graded absorbent is built using spraying methodology, and the 15 mm thick absorption layer is fabricated using extruding methodology. The mercury intrusion porosimetry experiments show that the sprayed matching layer incurs maximum porosity at 19.8% while the 3D extruded layer ensures the minimum porosity at 11.13%, strengthening the laminar grading effect to improve the EMW impedance matching. The Naval Research Laboratory experiments corroborate that double-layer structures improve the EMW-reflecting capacity compared to their single-absorption-layer counterparts and that the double-layer element containing the best wrapping effect absorbent yields the best reflection loss value, with a minimum of −14.7 dB and a 9.72 GHz effective bandwidth. The EMW-reflecting mechanism for the novel graded double-layer structure containing the graded nano-sized absorbent is then summarized. Theoretical calculations using the transform line theory suggest that a 15 mm absorbing layer and a 15 mm impedance matching layer is specified as the most optimized configuration, with −10.47 dB in average reflection, −15.18 dB in maximum RL, and 9.56 GHz in effective bandwidth. [ABSTRACT FROM AUTHOR]

Electromagnetic wave (EMW) pollution impairs the performance of equipment, facilities, information security, and human health. Ordinary, plain cementitious composite has limited EMW-reflecting capacity. To correct this, a macrostructure EMW absorbing element has been developed to reduce EMW pollution. As conventional casting of macrostructures is not cost-effective and lacks quality because of the demand for special formwork, 3D printing technology offers greater design flexibility, higher efficiency, and improved mechanical properties. Moreover, the surface texture of 3D-printed material exhibits natural corrugation to enhance EMW reflection further. In this study, novel wave-shaped EMW absorbing elements were fabricated using 3D cementitious printing technology. The EMW absorbing performance was analyzed by the naval research laboratory (NRL) system in the range of 1 GHz–18 GHz. Significant improvement of reflectivity was observed, especially in the low-frequency range. The optimum configuration was identified through effectiveness evaluation to be a K 3 sample with 45 mm of heave height and 2/3 tan(θ), exhibiting a minimum reflectivity −43.7 dB, mean reflectivity −25 dB, and an absorbing bandwidth of 18 GHz. The experimental reflectivity was also simulated by the finite element method, which agrees with the experimental results. The synthetic vector electromagnetic field distribution was also studied to explore space impedance characteristics. Moreover, the finite element method attempted to correct drawbacks in experiments, including multiple direction reflection measurement and wave-number interruption. Based on simulation calibration, the influence of wave-shaped parameters (heave height and tangent value) upon EMW absorbing capacity was induced accurately. [ABSTRACT FROM AUTHOR]