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To solve the serious electromagnetic radiations and provide a new application for low-quality fly ash (FA), FA was used as the cement replacement for enhancing the electromagnetic absorption of cement-based composites. The microstructure and electromagnetic parameters of FA were characterized by means of scanning electron microscope and vector network analyzer, respectively. The results showed FA has the potentialities for wave attenuation due to its complex components and porous structure. However, the pozzolanic activity and packing effect of FA has a negative effect on the absorbing properties of FA/cement. In contrast, the absorbing properties can be enhanced greatly by introducing expanded polystyrene and FA in cement composites together. The dielectric absorbents are more suitable than conductive powders for wave attenuation in FA/cement composites. When the specimen consists of 25% FA & 50% EPS & 6% MnO 2 , the bandwidth of reflection loss less than −8 dB is enlarged to 10.95 GHZ with a peak value of −15.2 dB at 5.5 GHz.

Fe-doped MnO 2 with a hollow sea urchin-like ball chain shape was first synthesized under a high magnetic field of 10 T. The formation mechanism was investigated and discussed in detail. The synthesized samples were characterized by XRD, SEM, TEM, EMPA, and vector network analysis. By doping MnO 2 with Fe, the relative complex permittivity of MnO 2 and its corresponding loss tangent clearly decreases, but its relative complex permeability and its corresponding loss tangent markedly increases. Moreover, the theoretically calculated values of reflection loss show that with increasing the Fe content, the as-prepared Fe-doped MnO 2 exhibits good microwave absorption capability.

To solve more and more serious electromagnetic radiations, cement-based composites were prepared by introducing porous materials into cement. The reflection losses were studied using arched testing method in the frequency range of 1.7–18 GHz. The results showed that the absorption properties were improved obviously. The mechanisms of wave attenuation of the composites were discussed, which indicated that the scattering and multi-scattering in porous beads played an important role. The filling ratio of porous beads, the bead geometries as well as the conformation of cement all had noticeably influence on the absorption properties. The lowest reflection loss of −22 dB was obtained at 5.6 GHz when the specimen was filled with 50 vol.% expanded polystyrene, and the effective absorption bandwidth (less than −10 dB) reached 10.6 GHz when the specimen was filled with 50 vol.% expanded polystyrene and 2 vol.% carbon black.

MnO 2 /doped polyaniline (PANI) is prepared by an in situ polymerization method using γ-MnO 2 as the addition agent and hydrochloric acid as the doping agent. Products are characterized by FT-IR, UV–vis, XRD, and TEM. Conductivity, electromagnetic properties, and microwave absorption properties are first discussed on the basis of structural characterization. The as-prepared products of MnO 2 /PANI are partially crystalline in nature and spherical in pattern with grain sizes of 50–70 nm. MnO 2 particles are successfully decorated with doped PANI. MnO 2 /PANI displays moderate electric conduction, excellent dielectric losses, and microwave absorption capabilities. Compared to pure MnO 2 , the dielectric and reflection loss properties of MnO 2 /PANI composites exhibit significant improvements, with an effective absorption band at 5 GHz under −10 dB and maximum reflection loss of −21 dB at 13.56 GHz. Pure MnO 2 shows an effective absorption band of 3 GHz under −10 dB and a maximum reflection loss of −14.20 dB at 11.5 GHz. Thus, MnO 2 /PANI composites are found to be a promising microwave absorption material.

MnO 2 powder was synthesized in a high magnetic field (8 T) via a simple route, and the formation mechanism for the grain shape was discussed. The synthesized samples were characterized by XRD, SEM, TEM, and vector network analysis. The morphology of synthesized MnO 2 was sea urchin-like ball chain with a low density center, just like “hollow-like”. Throughout the whole frequency range, the dielectric constant and the loss tangent clearly decreased in 8 T high magnetic field. Moreover, the magnetic permeability and the loss tangent increased slightly in the frequency range 2–13 GHz. Furthermore, the theoretically calculated values of reflection loss showed that when the magnetic field strength 8 T was adopted, the absorption peak became smoother and shifted to a higher frequency.

Redoped-polyaniline (PANI) was prepared by chemical redox polymerization of aniline using ammonium perdisulfate, (NH4) 2 S 2 O 8 , as an oxidant and hydrochloric acid, HCl, as a doping agent. The structural characterization based on FT-IR, UV–vis, XRD, TEM and electrical conductivity was first used to evaluate the thermal stability and the electromagnetic properties. The redoped-PANI was partial crystalline nature and similar spherical structure about 4–5 nm in diameter. The redoped-PANI displayed outstanding electric conduction and thermally stability. The volume resistivity was as high as 5.18 × 10 −1 Ω cm. Doped-PANI maintained stable conductibility at temperatures up to about 100 °C. The redoped-PANI had excellent dielectric properties, multiple Debye dipolar relaxation, and substantial microwave absorption capability. The values of ɛ ′ r and ɛ ″ r for the redoped-PANI powder were from 9.31 to 5.95 and 3.44 to 2.10, respectively. The maximum reflection loss of redoped-PANI composites of 2.0 mm thickness were −14.3 dB at 16.4 GHz and the effective absorption band under −10 dB was from 10.0 to 13 GHz.

MnO2 with a sea urchin-like ball chain shape was first synthesized in a high magnetic field via a simple chemical process, and a mechanism for the formation of this grain shape was discussed. The as-synthesized samples were characterized by XRD, SEM, TEM, and vector network analysis. The dielectric constant and the loss tangent clearly decreased under a magnetic field. The magnetic loss tangent and the imaginary part of the magnetic permeability increased substantially. Furthermore, the theoretically calculated values of reflection loss showed that the absorption peaks shifted to a higher frequency with increases in the magnetic field strength.

MnO2 with different morphologies and crystal structures were prepared via a low-temperature hydrothermal method in a stainless-steel autoclave at 120 °C at different dwell times. The products were characterized by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electromagnetic and microwave-absorption properties of the as-obtained MnO2 were reported. The results show that the different dwell times play a crucial role in the phase purity, the crystal structure, the morphology, and the electromagnetic properties of the products. The real and imaginary parts of the complex permittivity of the as-prepared MnO2 increased systematically with increasing dwell times, while the complex magnetic permeability values showed the contrary. The absorbing peak value of the reflection loss of the MnO2/paraffin wax visibly shifted to the lower frequency band with the increase in the reaction times of the MnO2 products. The microwave absorption properties of the MnO2 products were mainly attributed to both the dielectric and magnetic losses. In the total loss, however, the dielectric loss played the more important role, especially in the dielectric polarization loss versus frequency test.

Double-layer materials were devised in order to improve the absorbing properties of electromagnetic wave absorbing plates. The double-layer wave absorbing materials are composed of a matching layer and an absorption layer. The matching layer is the surface layer through which most of the incident waves can enter, and the absorption layer beneath it plays an important role in incident wave attenuation. The total thickness of the double layer is the sum of the thicknesses of these two layers. Carbonyl iron (CI) and carbon black (CB) were used as absorbents in the matching and absorption layers, respectively. The structures of the CI and CB particles were analyzed using scanning electron microscopy and transmission electron microscopy; the dielectric properties and absorption mechanisms were also studied. In the testing frequency range 2–18 GHz, the results show that the double-layer absorbers have two absorption peaks, and the positions and values of these peaks change with the content level of the absorbents. When the mass fraction of CI in the matching layer is 50% and the total thickness of the absorber is 4 mm, the effective absorption band (below −8 dB) reaches 5.5, 5.8, and 6.5 GHz. Where the mass fraction of CB is 50% or 60% and the mass fraction of CI is 70%, the bandwidth with reflection loss below −4 dB is larger than 10 GHz.

With the increase of electromagnetic pollution and the wide use of commercial and military products, there is an increasing interest in electromagnetic interference (EMI) shielding. This article mainly aims at the effect of high magnetic field (HMF) on the grain shape and electrical conductivity of HCl-doped polyaniline (Pani-HCl), and the electrical conductivity and EMI shielding effectiveness (SE) of the conducting composites made from silicone rubber (SR) with different loading levels of Pani-HCl (without HMF) in the low frequency range from 3 to 1500 MHz. The result indicates that SE of the composites containing Pani-HCl (without HMF) increases and the volume resistivity decreases with increasing mass ratio loading of Pani-HCl in the SR. The measured SE of the composites are from 16 to 19.3 dB at 100 mass ratio loading of Pani-HCl and the volume resistivity decreases nine orders of magnitude compared with that of the emeraldine base form of Pani (Pani-EB) composites. The influence of HMF on electrical conductivity and grain shape of Pani-HCl is great. The grain shape of the in situ polymerization of PAN in 10T is an open-ramified rod-like pattern with a diameter of 50 nm and that of secondary doped PAN in 10T change to spherical structures of diameter of about 20-30 nm, which are obviously different from the irregular reef-like particle shape of doped PAN in 0T. It is thought that the reason for the different grain shape is anisotropic diamagnetic susceptibility of doped PAN and orientations of the HMF.

With the increasing of electromagnetic pollution and the widely use of commercial and military products, there is an increasing interest in electromagnetic interference (EMI) shielding. This paper mainly aims at electrical conductivity and EMI shielding effectiveness (SE) of the conducting composites made from silicone rubber (SR) with different loading levels of HCl-doped polyaniline (PAN-HCl) in the low frequency range from 3 to 1500 MHz. The result indicates that SE of the composites increase and the volume resistivity decrease with increasing mass ratio loading of PAN-HCl in the SR. The measured SE of the composites are from 16 to 19.3 dB at 100 mass ratio loading of the PAN-HCl and the volume resistivity decrease nine orders of magnitude compared with that of the emeraldine base form of PAN (PAN-EB) composites.

Using the carbon coated expanded polystyrene (EPS) beads as filling admixture, the electromagnetic (EM) wave absorber more moistureproof and environment adaptive than the conventional absorber used in anechoic chamber was fabricated. The effective permittivity of the mixture with carbon volume content 1% was calculated by the strong fluctuation theory combining with Maxwell-Wagner theory; and the EM wave absorbing property of a laminated model filled with carbon coated EPS beads was predicted through calculation. Comparison with the experiment indicated that the results of calculation accorded with the experiment closely, and can be used for the design of the moistureproof EM wave absorber.

By measuring the electrical resistivity of RTV silicone rubber with Ni powder, t he percolation threshold of Ni-based conductive silicone rubber was determined. When N234 was filled in Ni-based conductive silicone rubber,double-percolation p henomenon was found other than percolation law. After fitting of the experimenta l results,the mechanism of the double-percolation phenomenon was presumed. As fo r the shielding effectiveness of high conductive silicone rubber, the result sh ows that it can be described well with the Schelkunoff theory.The influence of double-percolation phenomenon on shielding effectiveness of the rubber was investigated.