The rapid increase in electromagnetic interference has received a serious attention from researchers who responded by producing a variety of radar absorbing materials especially at high gigahertz frequencies. Ongoing investigation is being carried out in order to find the best absorbing materials which can fulfill the requirements for smart absorbing materials which are lightweight, broad bandwidth absorption, stronger absorption etc. Thus, to improve the absorbing capability, several important parameters need to be taken into consideration such as filler type, loading level, type of polymer matrix, physical thickness, grain sizes, layers and bandwidth. Therefore, this article introduces the electromagnetic wave absorption mechanisms and then reveals and reviews those parameters that enhance the absorption performance.

Microwave absorption properties were systematically studied for double-layer carbon black/epoxy resin (cB) and ni 0.6 Zn 0.4 fe 2 o 4 /epoxy resin (F) nanocomposites in the frequency range of 8 to 18 GHz. The ni 0.6 Zn 0.4 fe 2 o 4 nanoparticles were synthesized via high energy ball milling with subsequent sintering while carbon black was commercially purchased. The materials were later incorporated into epoxy resin to fabricate double-layer composite structures with total thicknesses of 2 and 3 mm. The CB1/F1, in which carbon black as matching and ferrite as absorbing layer with each thickness of 1 mm, showed the highest microwave absorption of more than 99.9%, with minimum reflection loss of −33.8 dB but with an absorption bandwidth of only 2.7 GHz. Double layer absorbers with F1/CB1(ferrite as matching and carbon black as absorbing layer with each thickness of 1 mm) structure showed the best microwave absorption performance in which more than 99% microwave energy were absorbed, with promising minimum reflection loss of −24.0 dB, along with a wider bandwidth of 4.8 GHz and yet with a reduced thickness of only 2 mm.In order to address issues induced by high proliferation of electromagnetic interferences in both civil and military applications, efficient microwave absorbers are becoming highly desirable and necessary. For that reason, such material is required to effectively reduce the reflection of electromagnetic (EM) signals over a broad absorption bandwidth. In order to improve the performance of microwave absorption properties, microwave absorbers are designed to meet the specific requirements of simultaneously having strong absorption, wide frequency band, lightweight and small thickness. Improvements can certainly be made to the designs by physical assembling of different types of absorbents 1-5 , chemical decorated absorbents 6,7 as well as by designing multi-layer structures [8][9][10][11] .Microwave absorbers are produced using different kinds of materials including one dimensional (1D) materials such as carbon nanotubes 12-15 , two dimensional (2D) materials such as graphene 16,17 and bulk three dimensional (3D) materials such as ferrites 9,18-21 . The difference in the dimensional structure of the materials would largely affect the microwave absorption performances since different kinds of structures contribute to different www.nature.com/scientificreports www.nature.com/scientificreports/ the F1/CB1 sample showed the best all round performance, in which more than 99% microwave energy was absorbed, with a reflection loss of −24.0 dB and a widest bandwidth of 4.8 GHz at −10 dB, yet it is the thinnest among the three designs, having a total thickness of only 2 mm.

This study investigates the structural, electrical and microwave properties of yttrium iron garnet (YIG) which focuses on the parallel evolving relationship with their dependence on the sintering temperature. The iron oxide obtained from the steel waste product (mill scale) was used to synthesize YIG. The raw mill scale underwent the milling and Curie temperature separation technique to produce high purity iron oxide powder which is the main raw material in preparing and fabricating YIG through high energy ball milling (HEBM) process. Microstructural features such as amorphous phase, grain boundary, secondary phase and intergranular pores contribute significantly to the additional magnetic anisotropy and demagnetizing fields, affecting the electric and microwave properties accordingly. The increment in electrical resistivity and decrement in linewidth while the microstructure was evolving is believed to be a strong indicator of improved phase purity and compositional stoichiometry.

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The enhancement of microwave absorbing properties in nickel zinc ferrite (Ni0.5Zn0.5Fe2O4) via multiwall carbon nanotubes (MWCNT) growth is studied in this research work. Ni0.5Zn0.5Fe2O4 was initially synthesized by mechanical alloying followed by sintering at 1200 °C and the microstructural, electromagnetic and microwave characteristics have been scrutinized thoroughly. The sintered powder was then used as a catalyst to grow MWCNT derived from chemical vapor deposition (CVD) method. The sample was mixed with epoxy resin and a hardener for preparation of composites. The composite of multi-walled carbon nanotubes/Ni0.5Zn0.5Fe2O4 shown a maximum reflection loss (RL) of −19.34 dB at the frequency and bandwidth of 8.46 GHz and 1.24 GHz for an absorber thickness of 3 mm for losses less than −10 dB. This acquired result indicates that multi-walled carbon nanotubes/Ni0.5Zn0.5Fe2O4 could be used as a microwave absorber application in X-band.