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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

WOS: 000528575100001, A novel multiband metamaterial absorber (MTMA) is proposed which is capable of well presenting a polarization-insensitive and wide incident angle stability in the microwave frequency range. The proposed MTMA comprising two vertically stacked asterisk-based copper resonators separated by dielectric layer of flame retardant type four and backed with a thin copper film. High-frequency structure simulator was used to simulate the absorber and to depict surface current distribution. The results showed that the absorber is operated at three narrow bands with high absorptivity of about 92, 100 and 100% at frequencies of 2.75, 4.3 and 9.5 GHz, respectively. The position of the resonant peaks can be effectively tuned by adjusting the geometry parameters of the structure, thereby achieving a multiband, polarization-independent and wide-angle absorber. The designed structure is important for the application of sensors, thermal images and in constructing broad multiband signals for electromagnetic compatibility/interference., National Key Research and Development Program of China [2017YFA0204600]; National Natural Science Foundation of ChinaNational Natural Science Foundation of China [51802352]; Central South University [2018zzts355], We are grateful to the National Key Research and Development Program of China (Grant No. 2017YFA0204600), the National Natural Science Foundation of China (Grant No. 51802352) and Central South University under Grant No. 2018zzts355.

A cross-shaped metamaterial absorber (CSMMA) has been introduced to integrate with two-layered polyurethane foam absorbers (PUFAs). By incorporating with CSMMA, microwave absorptive performance of the proposed PUFAs in 8–18 GHz has been remarkably improved for various oblique incident angles under the transverse electric (TE) and transverse magnetic (TM) waves. For the TE wave, the effective bandwidths of −10 dB reflection loss for the PUFAs incorporated with CSMMA increase by 0.85 GHz, 1.15 GHz, 1.25 GHz, 1.50 GHz and 1.70 GHz for 0°, 15°, 30°, 45° and 60°, respectively. As for the TM wave, the effective bandwidths of −10 dB reflection loss for the modified PUFAs by CSMMA rise by 0.85 GHz, 1.10 GHz, 1.20 GHz, 2.85 GHz and 2.90 GHz for 0°, 15°, 30°, 45° and 60°, respectively. The proposed PUFAs optimized by CSMMA could operate well at incident angles ranging from 0° to 60° for both TE and TM waves. In addition, the different variation rules of absorption peak intensity of CSMMA have been revealed through the magnetic field distributions under TE and TM waves. Results indicate that PUFAs combined with CSMMA can be utilized for microwave absorbers adapting to both TE and TM waves at various oblique incident angles. Keywords: Wide-angle absorption, Polyurethane foam, Metamaterial absorber, Electromagnetic field distribution

The corresponding mechanism of high complex permittivity for micro flaky Fe-filled composites was still not apparent. In this letter, the dielectric behaviors of flaky carbonyl iron/epoxy resin composites within 2–18 GHz were studied experimentally and theoretically. Results show that an obvious increase both in real and imaginary part of permittivity can be observed as the volume fractions of FCI is up to the percolation threshold. Considering the influence of conduction current, a revised Debye model of permittivity has been proposed to reveal the mechanism of dielectric behavior in composites. The best fitting result demonstrate that conduction loss played an important role in increasing the permittivity after percolation. Fe3O4 was used as encapsulated shell on surface of the FCI to control the conduction and enhance the percolation threshold, resulting in better microwave absorption from better balance between the complex permittivity and permeability.

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 optimized NiZn ferrite absorber for the whole P-band (230 –1000 MHz) is proposed by inserting cross-shaped metamaterial. Effective absorption bandwidth below − 10 dB for the composite absorber covers the frequency range 210 MHz–1000 MHz. Electromagnetic wave attenuation mechanisms are revealed by surface current distribution and power loss density distribution. The increased absorption bandwidth of the composite absorber is attributed to the overlap effect of three absorption peaks originated from the multilayer cross-shaped metamaterial absorbers. Results indicate that the proposed composite absorber can be utilized in the P-band with relatively less thickness compared to the traditional NiZn ferrite absorber.

A broadband and wide-angled microwave absorber based on resistive-type metamaterial has been proposed and demonstrated in the low-frequency regime of 2–8 GHz. The minimum reflection loss of the absorption peak located at 5.27 GHz is −51.41 dB. Effective bandwidth better than −10 dB reflection loss is able to achieve 2.70 GHz in the range from 3.81 GHz to 6.51 GHz. The underlying physical mechanisms of electromagnetic wave energy attenuation are illustrated in detail by means of surface current, electromagnetic field and power loss density. Furthermore, the influence of structural dimensions on the attenuation properties of the proposed resistive-type metamaterial absorber is also investigated. More importantly, the designed resistive-type metamaterial absorber could operate well with incident angles changing from 0[Formula: see text] to 60[Formula: see text] under the transverse electric (TE) and transverse magnetic (TM) waves. Research results will be capable of providing guidance for the design and preparation of broadband microwave absorbing materials at low frequencies.

An optically transparent metamaterial absorber (MMA) has been demonstrated numerically and experimentally at the S-band. The designed MMA is composed of polymethyl methacrylate (PMMA), indium-tin-oxide (ITO) attached to polyethylene terephthalate (PET) film, and numerically provides effective absorption with reflection loss lower than −10 dB in the frequency range of 1.85–4.65 GHz. Experimental measurement shows the reflection loss of the proposed MMA is better than −10 dB from 2.00 GHz to 4.25 GHz, which agrees pretty well with the simulated results. Distributions of surface current, electromagnetic field and power loss density for the designed MMA are systematically investigated to explain microwave attenuation characteristic and loss mechanisms. More importantly, the prepared sample exhibits an optical transparency above 68% in the whole visible band, thus realizing a wide range of applications, such as optically transparent S-band absorbers.

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

A metal-dielectric-metal (MDM) sandwich metamaterial perfect absorber (MPA) with magnetic nickel metal has been designed. An optimal absorption of 99.28% at 404 MHz is achieved for MPA with thickness of 5.54 mm. Resonant absorption is demonstrated to be main mechanism according to analyses on surface current distributions and electromagnetic field distributions. Furthermore, the electromagnetic energy is mainly dissipated in magnetic metal with magnetic loss proportion of 55.43% by comparatively analyzing the wave-absorbing performance of using magnetic metal, non-magnetic metal and perfect electric conductor (PEC) as metallic layers. These results would provide a guidance for the design of quasi-microwave absorbing/shielding materials.

Lead-free magnetoelectric (ME) laminated (80Bi0.5Na0.5TiO3-20Bi0.5K0.5TiO3)/(Ni0.8Zn0.2)Fe2O4 (BNKT/NZFO) composites are prepared via a modified cofiring processing, combining grain refinement and liquid phase sintering with low sintering aid content. The microstructure, dielectric, ferroelectric, magnetic, and magnetoelectric properties are investigated by varying the thickness of NZFO layer. The results show that the coexistence of independent BNKT and NZFO phase and the presence of the morphotopic phase boundary in BNKT phase with high piezoelectric coefficient d33 of 131 pC/N are confirmed. Laminated composites have clear and well-bonded interfaces across the two layers, as well as improved ME properties. The maximum ME voltage coefficient (αE31) of the laminated composite reach 115.1 mV cm−1 Oe−1 with an optimized BNKT/NZFO layer thickness ratio of 1/2. In addition, a zero-biased ME response was observed in BNKT/NZFO laminated composites.

Lead-free multiferroic ceramics consisting of (1-x) (80Bi0.5Na0.5TiO3-20Bi0.5K0.5TiO3) (BNT-BKT)-xNi0.8Zn0.2Fe2O4 (NZFO) (x = 0, 0.15, 0.25, 0.35, and 0.45) were synthesized by the in situ sol-gel method. The structural, ferroelectric, piezoelectric, ferromagnetic, and magnetoelectric (ME) properties were measured as a function of the NZFO content x. The results showed that the coexistence of BNT-BKT and NZFO phases and the presence of the morphotropic phase boundary in the BNT-BKT phase with a high piezoelectric coefficient d33 (∼131 pC/N) were confirmed. The composites exhibited a homogeneous microstructure and well-combined interfaces between the magnetostrictive and piezoelectric phases, as well as an improved ME response. The largest ME voltage coefficient (αME) of 42.41 mV/cm Oe was achieved for the 0.65(BNT-BKT)-0.35NZFO composite, which is in fact the highest one reported so far for lead-free particulate ME composites fabricated via in situ processing.