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In view of the problem of heavy weight of the low-frequency band metamaterial absorber, the weight of the metamaterial absorber is mainly concentrated in the medium dielectric substrate. Different from the previous metamaterial absorbers based on continuous dielectric substrate, a new lightweight metamaterial absorber based on discontinuous dielectric medium is proposed and verified in the L-band (1–2 GHz). Compared with metamaterial absorber based on the continuous dielectric substrate, the weight of the metamaterial absorber designed based on discontinuous media is reduced by 42.58%. The dual-peak reflection losses of −17.29 dB and −15.99 dB are obtained at 1.23 GHz and 1.72 GHz, respectively. Our work provides a new method for constructing light dual-peak metamaterial absorbers in the L-band. [ABSTRACT FROM AUTHOR]

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 ∘ to 60 ∘ 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In order to investigate the effect of magnetic metal on the absorption performance of metamaterial absorber (MMA), a dual-peak MMA based on magnetic metal nickel is designed and demonstrated in the P-band (300–1000 MHz). Two-layer square-ring-metal resonator arrays and two-layer dielectric substrates are arranged alternately with each other to constitute the proposed dual-peak MMA backed with a reflective metal plate. The influences of copper or nickel metallic layers on the absorption coefficients are comparatively analyzed. For the nickel MMA, the dual-peak absorption coefficients of 99.82% and 99.09% are achieved at 394 MHz and 605 MHz, respectively. Moreover, the thickness of dual-peak MMA could be reduced to 9 mm by employing magnetic metal nickel. The physical mechanism of dual-peak absorption is illustrated by surface current distributions, magnetic field distributions and power loss density distributions. The relationship between the changes of geometric dimensions and the shift of peak absorption frequencies is ultimately discussed. These results could provide instructive guidance for realizing a thin dual-peak MMA in the P-band. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

• Shell-core structured C@Ni 0.5 Zn 0.5 Fe 2 O 4 nanoparticles have been successfully synthesized by the tannic acid coating method. • Minimum reflection loss of the C@Ni 0.5 Zn 0.5 Fe 2 O 4 –5:1–900℃ sample is −26.87 dB at 4.3 GHz, and the effective absorption bandwidth is 4.05 GHz. • Microwave absorption performance can be controlled by adjusting the annealing temperatures and shell-core mass ratios. • The microwave attenuation mechanisms are discussed in detail. C@Ni 0.5 Zn 0.5 Fe 2 O 4 nanoparticles with different annealing temperatures and shell-core mass ratios were synthesized by a tannic acid coating method. Through SEM, TEM, EDS and XRD characterization, the as-prepared product was confirmed to be shell-core structured C@Ni 0.5 Zn 0.5 Fe 2 O 4 nanoparticles with an average diameter of approximately 650 nm, and a carbon layer was deposited on the surface of the product. Compared with uncoated NiZn ferrite, the carbon-coated NiZn ferrite exhibits a moderate real part and imaginary part of its complex permittivity, while maintaining high permeability, which improves the impedance matching characteristics and microwave loss performance of the material. When the shell-core mass ratio was 9:1 and the annealing temperature was 900 °C, the as-prepared sample exhibited advanced microwave absorption performance with a minimum reflection loss (RL) of -26.87 dB at 4.3 GHz with a matching thickness of 1.8 mm, and the effective absorptive bandwidth was approximately 4.05 GHz when the RL was below -10 dB. [Display omitted] [ABSTRACT FROM AUTHOR]

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. • The designed metamaterial absorber with second-order cross structure shows strong microwave absorption and good optical transmittance. • The reflection loss is lower than -10dB in 3.98~8.68 GHz range. • The average optical transmittance is about 75% in 390~780 nm range. [ABSTRACT FROM AUTHOR]

A novel single-layer graphene-based structure is designed in this article. This structure consists of two graphene strips and two graphene blocks. The components of this structure generate two bright modes and one dark mode in the terahertz region, and these three modes undergo destructive interference, leading to the phenomenon of double plasmonic induced transparency. The graphene of this structure has continuity, and the Fermi level can be adjusted by adjusting the bias voltage applied to the structure. Compared with those discontinuous structures, it is easier to achieve tuning function. The structure uses the finite-difference time-domain for data simulation, uses the coupled mode theory for theoretic calculation, and compares the transmission spectra obtained by the two methods. Through observation, it can be found that the frequency positions of the peaks and dips of the simulated transmission spectrum increase with the increase of the Fermi level, showing a perfect linear relationship, which indicates that this structure has great prospects in the modulator. In addition, the structure has achieved good results in the slow light effect, and after measurement, the peak values of group index and group delay can reach up to 380 and 0.241 ps, respectively. By utilizing these advantages, this structure can provide more possibilities for the development and research of slow light fields. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A chaos patterned metasurface absorber (CPMA) with three strong absorption peaks and a wide bandwidth has been designed. This CPMA presents a single-layer sandwich structure, which not only enables easy optimization by adjusting the surface pattern and model size but also contributes to the continuous effective bandwidth (EBW, with an absorptivity larger than 90%) from the multiple adjacent absorption peaks. The continuous EBW is from 4.28 to 9.56 GHz with a bandwidth of 76.3%. Meanwhile, analyses on the distributions of the surface current, electric field, and power loss density illustrate that the absorption mechanisms are mainly magnetic coupling resonance and dielectric loss. The experimental results confirm the good absorption performance with multi-peak and wide bandwidth for the fabricated CPMA sample, which shows potential applications in the field of anti-electromagnetic interference. [ABSTRACT FROM AUTHOR]

The complementary-modeled Rossler chaotic metamaterial (CRCM) with FR-4 dielectric layer is proposed to design metamaterial absorber with multi-resonance peaks. Under "master-slave" boundary condition in high-frequency structure simulator (HFSS) software, the electric field between adjacent boundaries presents phase difference which can simulate an infinite array. The research results show that the CRCM demonstrates multi-resonant peaks from 4 GHz to 10 GHz, and the area of metal patterned-layer can obviously regulate the resonant peaks. The CRCM presents a linear polarization conversion peak around 5.80 GHz, its polarization conversion ratio (PCR) is near 100%. The PCR is also larger than 80% from 5.56 GHz to 5.95 GHz. Through the surface current density distribution and the comparison between the CRCM and complementary-modeled double ring metamaterial (CDRM), the main factors generating polarization conversion are the asymmetry of metal pattern layer and magnetic resonance caused by reverse current. The CRCM also has two strong absorption peaks located at 6.31 and 9.37 GHz, respectively. Dielectric loss and ohmic loss are the main microwave loss mechanisms proved by volume and surface power loss density distribution. The resonant frequencies derived from L – C resonant circuit are well consistent with the simulation data and measurement results. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Development of microwave absorption technology triggers higher requirements for the multi-function of microwave absorbing materials. An optically transparent and mechanically stretchable wave-absorbing metamaterial based on fractal structure has been proposed numerically and experimentally in the microwave low frequency range. It is designed to possess two spectrally overlapped resonances located at 4.42 GHz and 7.02 GHz, which originate from the first-order cross resonance and the second-order cross resonance, respectively. Microwave absorbing mechanisms are elaborated by normalized impedance, surface current and power loss density. Moreover, the optical transmittance of the designed wave-absorbing metamaterial is higher than 70 % in the visible region. By stretching the absorber, the frequencies of two resonant peaks occur remarkable red shift with a adjustable frequency band range of 0.64 GHz. The corresponding relationship between the variation of substrate thickness and square resistance and the shift of peak absorption frequencies is discussed. Ultimately, the wave-absorbing performance of the proposed wave-absorbing metamaterial are illustrated at different incident angles for both TE and TM waves. Research results could provide and enrich instructive guidances for realizing optically transparent and mechanically stretchable metamaterial absorber. • The designed metamaterial absorber based on fractal structure was successfully prepared. • The proposed metamaterial absorber possesses strong microwave absorption and high optical transmittance simultaneously in the low frequency range. • Reflection loss of the proposed metamaterial absorber is better than − 10 dB from 3.86 GHz to 8.04 GHz. • Optical transmittance of the designed wave-absorbing metamaterial is higher than 70 % in the visible region. [ABSTRACT FROM AUTHOR]

This paper is aimed at acquiring functional ceramics with broadband magnetoelectric (ME) response for sensing wide-range of dc bias magnetic field. Three-phase particulate ceramics CoFe2O4/Ni0.8Zn0.2Fe2O4/Bi0.5Na0.4K0.1TiO3 (CFO/NZFO/BNKT) were fabricated, and the effect of magnetostrictive phase on the piezoelectric, magnetic, and ME properties were investigated systematically. Separated phases and homogeneous microstructure of the magnetostrictive and piezoelectric phases were confirmed. The variation in magnetostrictive coefficient with dc magnetic field was found to be markedly dependent on the relative content of magnetostrictive microparticles. By merging the nonlinear piezomagnetic response of the two ferrite components together, the ME composites present dual-peak bands. A wide-range ME coefficient was achieved over a magnetic range of 1800 Oe with large ME value of 20 mV/cm Oe. This field-conversion broadband ME behavior indicates that three-phase particulate ME ceramics are quite preferable for practical applications in magnetic field sensor. [ABSTRACT FROM AUTHOR]

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 Ba 12 Fe 28 Ti 15 O 84 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 Ba 12 Fe 28 Ti 15 O 84 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 Ba 12- x La x Fe 28 Ti 15 O 84 (x = 3) sample, showing a broadened absorption bandwidth (RL < -10 dB) covering the nearly X-band. In addition, microwave absorption mechanism of the doped ceramics was discussed. • Single-phase Ba 12 Fe 28 Ti 15 O 84 samples were prepared by a modified sol-gel method. • The introduction of La into Ba 12 Fe 28 Ti 15 O 84 enhances the magnetic properties and improves impedance matching characteristic. • A significant enhancement of microwave absorption property was observed for the doped Ba 12 Fe 28 Ti 15 O 84. [ABSTRACT FROM AUTHOR]

• The infrared emissivity presents periodical fluctuation phenomenon along edge length. • The peaked frequency is inclined to shift towards lower region with area ratio increased. • There exists intrinsic attenuation which is probably attributed to the diffuse scattering. 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. [ABSTRACT FROM AUTHOR]

Highlights • Ti 3 SiC 2 encapsulated by magnetic Ni 0.5 Zn 0.5 Fe 2 O 4 shell were successfully prepared. • Moderated complex permittivity for the Ni 0.5 Zn 0.5 Fe 2 O 4 /Ti 3 SiC 2 was achieved. • Desirable higher complex permeability for the Ni 0.5 Zn 0.5 Fe 2 O 4 /Ti 3 SiC 2 was realized. • The Ni 0.5 Zn 0.5 Fe 2 O 4 /Ti 3 SiC 2 coating with wide bandwidth (RL <-10 dB) of 5.3 GHz. Abstract Ti 3 SiC 2 particles encapsulated by Ni 0.5 Zn 0.5 Fe 2 O 4 shell were in-situ synthesized via a facile sol-gel method. Effects of Ni 0.5 Zn 0.5 Fe 2 O 4 shell on electromagnetic properties of Ti 3 SiC 2 were investigated in 2–18 GHz. Moderated complex permittivity and desirable higher complex permeability presented for the Ni 0.5 Zn 0.5 Fe 2 O 4 /Ti 3 SiC 2 composite, resulting in strong microwave attenuation ability and good impedance matching property. The measured effective absorbing bandwidth (RL < −10 dB) of 5.3 GHz and corresponding maximum RL of −38.6 dB were obtained for the Ni 0.5 Zn 0.5 Fe 2 O 4 /Ti 3 SiC 2 absorbing coating of 1.2 mm thickness. These results indicate that the Ni 0.5 Zn 0.5 Fe 2 O 4 /Ti 3 SiC 2 composite may become a new type of microwave absorbent. [ABSTRACT FROM AUTHOR]

The effects of Co 2 O 3 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 Co 3+ 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Particulate magnetoelectric (ME) ceramics constituted by (1- x )(80Bi 0.5 Na 0.5 TiO 3 -20Bi 0.5 K 0.5 TiO 3 )- x CoFe 2 O 4 [(1- x )BNKT- x CFO] ( 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 M 2 . 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. [ABSTRACT FROM AUTHOR]

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 <−10 dB) of 5.36 GHz is achieved in modified sample with the thickness of 1.5 mm, which is a promising microwave absorbing material in 2–8 GHz. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]