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Recent progress in exploring and developing new microwave absorbing materials is highlighted. In this paper, we reported on microwave electromagnetic properties of the novel quaternary ferrite La-substituted Ba12Fe28Ti15O84 prepared via a modified sol-gel method. A systematic study was conducted to identify the effects of La substitution on structure, conductive, dielectric, magnetic and microwave absorbing properties. The modified samples had a monoclinic crystal structure and exhibited dense plate-like grains. The introduction of La into Ba12Fe28Ti15O84 had a remarked influence on conductive behavior, dielectric and magnetic properties and in turn provided the tunable microwave electromagnetic properties. A significant enhancement of reflection loss (RL) was observed for the Ba12-xLaxFe28Ti15O84 (x = 3) sample, showing a broadened absorption bandwidth (RL

Composites or structures with adequate infrared reflection and microwave transmission are favorable from practical point of view. In this paper, oriented flaky aluminum filled pyramidal-frustum shaped periodic coatings was developed, and the effect of area of flaky aluminum powder filled coating on the infrared emissivity as well as microwave transmission behavior was intensively studied combined experiments with simulation. Results shown that the increments of oriented flaky aluminum filled coating could effectively reduce infrared emissivity. After spraying flaky aluminum filled periodic structures on the microwave absorbing material, the frequency corresponding to minimal reflection loss is inclined to shift towards lower frequency. Numerical simulation results shown that reflection coefficient gradually increases with increasing in frequency and area ratio of flaky aluminum filled coating. Besides, there exists intrinsic attenuation of flaky aluminum filled pyramidal-frustum shaped periodic coating, which is probably attributed to the diffuse scattering within step edge region.

Ti3SiC2 particles encapsulated by Ni0.5Zn0.5Fe2O4 shell were in-situ synthesized via a facile sol-gel method. Effects of Ni0.5Zn0.5Fe2O4 shell on electromagnetic properties of Ti3SiC2 were investigated in 2–18 GHz. Moderated complex permittivity and desirable higher complex permeability presented for the Ni0.5Zn0.5Fe2O4/Ti3SiC2 composite, resulting in strong microwave attenuation ability and good impedance matching property. The measured effective absorbing bandwidth (RL

The effects of Co2O3 addition on the electromagnetic properties of NiCuZn ferrite were investigated, by considering the variation of complex permeability, complex permittivity and quasi-microwave absorption property in the 1–1000 MHz frequency range. Results show that the introduction of Co3+ ions in NiCuZn ferrite leads to the marked shifting of magnetic resonance towards high-frequency and a slight increase of the permittivity. These Co-related effects enhance the maximum reflection loss in NiCuZn ferrite to reach −55.1 dB with its absorption bandwidth being tunable in the frequency range 480–1000 MHz, which provides a potential absorber for the anti-electromagnetic interference applications in electronic industry.

In this paper, we investigated the effect of magnetic grain size on magnetoelectric responses of particulate magnetoelectric 0.7(Bi 0.5 Na 0.5 TiO 3 -Bi 0.5 K 0.5 TiO 3 )−0.3(Ni 0.8 Zn 0.2 )Fe 2 O 4 (BNKT-NZFO) composites. The coexistence of two chemically separated phases was confirmed using x-ray diffraction analysis. The composites had homogeneous microstructure with controlled grain size. The magnetoelectric response of the BNKT-NZFO composites sensitively depended on the grain size of the NZFO phase and the magnetoelectric voltage coefficients presented a marked enhancement of 33% in the engineered grain size range. This result indicated that tailoring the magnetic grain size physically will provide a powerful mean of enhancing magnetoelectric coupling in a two-phase particulate composite, with large potential application in area of magnetic field sensor.

Particulate magnetoelectric (ME) ceramics constituted by (1-x)(80Bi0.5Na0.5TiO3-20Bi0.5K0.5TiO3)-xCoFe2O4 [(1-x)BNKT-xCFO] (x = 0, 0.1, 0.2, 0.3, 0.4 and 1.0) were synthesized by an powder-in-sol precursor hybrid processing method and their structure, magnetic, ferroelectric, magnetodielectric (MD) and ME properties have been investigated. Results showed that the ceramics consisted of only two chemically separated phases and had homogeneous microstructure. The introduction of CFO into BNKT matrix led to the weakening of ferroelectric and dielectric properties whereas the strengthening magnetic and MD properties. The observation of the MD effect revealed the evidence of the strain-induced ME coupling and the MD value is well scaled with M2. A maximum value of ME output of 25.07 mV/cm·Oe was achieved for the 0.7BNKT-0.3CFO composite. The improved ME response together with the linear MD effect makes the ceramics promise for use in magnetic field controllable devices or magneto-electric transducers.

The magnetic insulator Fe 3 O 4 -modified flaky Fe 85 Si 9.5 Al 5.5 (FeSiAl) powders with significantly enhanced electromagnetic wave absorption properties in the frequency range of 2–8 GHz were prepared by chemical co-precipitation. X-ray diffraction (XRD) and scanning electron microscopy (SEM) have confirmed the formation of nanoparticles Fe 3 O 4 precipitated on the flake-shaped FeSiAl. The electromagnetic measurements of the modified flakes presents a nearly invariable complex permeability and decreased complex permittivity in the 2–8 GHz, as well as improved impedance matching performance. More importantly, an excellent microwave absorbing performance with the bandwidth (RL

The single-phase Bi 1- x Nd x FeO 3 ( x =0, 0.05, 0.10, 0.15, 0.20) were synthesized by the sol-gel method. Their crystal structure and microwave electromagnetic property in the frequency range of 2–18 GHz were investigated. The XRD patterns and Raman spectra showed that structural transition from rhombohedral ( x =0, 0.05, 0.1) to triclinic ( x =0.15) and tetragonal structure ( x =0.20) appeared in the Bi 1- x Nd x FeO 3 . Electromagnetic measurement suggested that both microwave permeability μ′ and magnetic loss tanδ m increased remarkably over 2–18 GHz by doping Nd. Strong dielectric loss peak was observed on the samples of Bi 1- x Nd x FeO 3 ( x =0.15) and Bi 1- x Nd x FeO 3 ( x =0.2). Results show that Nd substitution is an effective way to push BiFeO 3 to become microwave absorbing materials with high performance.

An optically transparent metamaterial absorber (MMA) operated in the C-band (4–8 GHz) is optimally designed based on the second-order cross fractal structure. The experimental results show that the reflection loss of the proposed MMA is lower than −10 dB from 3.98 GHz to 8.68 GHz. Two overlapped resonances located at 4.77 GHz and 7.33 GHz, respectively, are caused by the second-order cross fractal structure. Distributions of surface current, electromagnetic field and power loss density are investigated to illustrate the absorptive characteristics and electromagnetic loss mechanisms of the proposed MMA. Moreover, the average optical transmittance of the MMA is close to 75% from 390 nm to 780 nm. The MMA possesses simultaneously strong absorptive capacity in the C-band and high transmittance in the visible light range, showing potential application in special environment.

Cross-shaped resonators were proposed to improve the light absorption in the organic active layers, namely P3HT, PCBM and P3HT:PCBM hetero-structure. The resonator was made of aluminium (Al) which was encrusted on top of the organic active layers backed with indium tin oxide (ITO) coated glass. Simulated results showed that the proposed structure had significantly enhanced the light absorption in the organic thin films, whereby exhibited a broadband absorption in the visible and infrared spectra. An obvious redshift in the characteristic absorption peak of the organic thin films was observed, resulting in the reduction of their apparent energy gap due to the coupling effect between cross-shaped resonator and organic active layer as a consequence of light-matter interaction. It is concluded that the proposed metamaterial structure is beneficial to improve the performance of organic solar cells. Keywords: Metamaterial, Organic thin film, Light absorption, Cross resonator, Solar cell