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The presence of impurities from raw materials directly affects the crystal shape control, process, and product performance of high-strength α-hemihydrate gypsum (α-HH,α-CaSO4•0.5H2O) from industrial by-product phosphogypsum (PG). In this work, effect of sodium fluoride on the crystal regulation of high-strength α-HH using calcium sulphate dihydrate(DH,CaSO4•2H2O) and PG as raw materials were investigated, respectively. The results showed that 0.6–1.8 wt% sodium fluoride can transform some α-HH crystals from fine needle shape to aggregate plate shape by changing the crystallinity, crystal habit and crystal diameter of α-HH. In the presence of 0.1 wt% citric acid and 0.6–1.8 wt% sodium fluoride, short hexagon-prism α-HH crystals can be obtained from DH or PG, sodium fluoride improved the content of α-HH in dehydration products, altered the dehydration and phase transition peak temperatures, transformed the crystallinity and crystal growth habit along the c-axis by the selectively chemisorption of F−, Na+ and citrate ions on the end surface of α-HH. With 0.1 wt% citric acid and 1.8 wt% sodium fluoride addition, the compressive strength of α-HH from DH and PG reached 59.8 MPa and 54 MPa, respectively, which were 54.3 MPa and 54.0 MPa higher than the blank samples. [ABSTRACT FROM AUTHOR]

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 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]

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 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]

A dual-band microwave metamaterial absorber with single-peak regulation and wide-angle absorption has been proposed and illustrated. The designed metamaterial absorber is consisted of hollow-cross resonators, solid-cross resonators, dielectric substrate and metallic background plane. Strong absorption peak coefficients of 99.92% and 99.55% are achieved at 8.42 and 11.31 GHz, respectively, which is basically consistent with the experimental results. Surface current density and changing material properties are employed to illustrate the absorptive mechanism. More importantly, the proposed dual-band metamaterial absorber has the adjustable property of single absorption peak and could operate well at wide incidence angles for both transverse electric (TE) and transverse magnetic (TM) waves. Research results could provide and enrich instructive guidances for realizing a single-peak-regulation and wide-angle dual-band metamaterial absorber. [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]

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]

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]

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]

A high-performance microwave absorption material is highly demanded. Herein, the laminated Ti3C2 Mxene was synthesised via HF etching process, and the flaky carbonyl iron (FCI) particles were prepared by high-energy ball milling. The hybrid Ti3C2/FCI powders with different mass ratios were fabricated by ultrasonic mixing method. Electromagnetic and microwave absorption properties of the single layer Ti3C2/FCI coatings were investigated in 2–18 GHz. A broadened microwave absorption property can be realized by optimizing the Ti3C2 and FCI content. Especially, the coating with 20 wt% Ti3C2 and 40 wt% FCI loading presents the measured absorption bandwidth (RL < − 10 dB) of 8.16 GHz with the thickness of 1.0 mm. The remarkable microwave absorbing performance was attributed to the good impedance matching and moderate attenuation ability. These results indicate that the Ti3C2/FCI composites have great potential to be a broadband microwave absorbent. [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]

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. [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]

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]