Microstructure and microwave electromagnetic properties of Dy^(3+)-doped W-type hexaferrites

Ba 1 x Dy x Co 2 Fe 16 O 27 （x = 0.00, 0.05, 0.10, 0.15, and 0.20） was prepared by the solid-state method. The phase structure was studied using powder X-ray diffraction （XRD）, the electromagnetic properties were measured, and the reflection loss of Dy 3＋ -doped ferrite material was calculated using electromagnetic parameters by the transmission line theory. All XRD patterns showed the single phase of the magnetoplumbite barium ferrite without other intermediate phase when x ≤ 0.15. The values of ε ′ and ε ″ increased slightly with Dy 3＋ ions doping. The values of μ″ and μ′ were improved with Dy 3＋ doping, exhibiting excellent microwave magnetic performance. The reasons have also been discussed using the electromagnetic theory. Dy substitution could increase microwave-absorbing performance and broaden frequency band （reflection loss （RL） -10 dB）, and the absorbing peak shifted to high-frequency position. When x = 0.2, ferrite layer exhibited the most excellent microwave-absorbing performance at a thin matching thickness of 1.5 mm. The peak value of RL was around -15 dB, and the frequency band （RL -10 dB） was about 7 GHz （from 8 to 15 GHz）.

Influences of La^(3+) Substitution on Structure and Electromagnetic Properties of Nanocrystalline Nickel Ferrites

Nanocrystalline nickel ferrites with substitution of Fe3+ by rare-earth La3+, according to the formula NiLaxFe2-xO4 (with x=0, 0.05, 0.1 and 0.15), were prepared by polyacrylamide gel method. Influences of the amount of La3+ substitution on the structure and electromagnetic properties of NiLaxFe2-xO4 compounds were systematically investigated by DSC-TG, XRD, TEM and wave-guide method. XRD results indicated that the pure spinel-type crystal structure of the NiLaxFe2-xO4 (x=0 and 0.05) was obtained at 500 ℃. TEM results showed that the average particle sizes of NiFe2O4 and NiLa0.1Fe1.9O4 particles were about 10 and 15 nm, respectively. The complex permittivity and complex permeability was measured in the frequency range of 8.2～12.4 GHz. The results revealed that the nanocrystalline NiLaxFe2-xO4 had both dielectric loss and magnetic loss in the frequency range of 8.2～12.4 GHz. The tgδε and tgδm of NiLaxFe2-xO4 (with x=0 and 0.05) decreased with the increase of La3+ ions content, and some strong resonance peaks of the tgδε and tgδm of NiLaxFe2-xO4 (with x=0.1 and 0.15) appeared because of the secondary phases (LaFeO3) and more lattice defects.

Effect of polyacrylamide on morphology and electromagnetic properties of chrysanthemum-like ZnO particles

Through hydrothermal process, the chrysanthemum-like ZnO particles are prepared with zinc acetate dihydrate （Zn（CH3COO）2·2H2O） and sodium hydroxide （NaOH） used as main resources under the different concentrations of surfactant polyacrylamide （PAM）. The microstructure, morphology and the electromagnetic properties of the as-prepared products are characterized by high-resolution transmission electron microscopy （HRTEM）, field emission environment scanning electron microscope （FEESEM） and microwave vector network analyzer, respectively. The experimental results indicate that the as-prepared products are ZnO single crystalline with hexagona wurtzite structure, that the values of slenderness ratio Ld are different in different PAM concentrations, and that the good magnetic loss property is found in the ZnO products, and the average magnetic loss tangent tan δu increases with PAM concentration increasing, while the dielectric loss tangent tan ~e decreases.

Enhancement of Heat-Resistance of Carbonyl Iron Particles by Coating with Silica and Consequent Changes in Electromagnetic Properties

Silica-coated carbonyl iron particles （CIPs） are fabricated with the Stober method to improve their heat-resistance and wave-aSsorption properties. The morphology, heat-resistance, electromagnetic properties and microwave absorption of raw-CIPs and silica-coated CIPs are investigated using a scanning electron microscope, an energy dispersive spectrometer, a thermal-gravimetric analyzer, and a network analyzer. The results show that the heat-resistance of silica-coated CIPs is better than that of raw CIFs. The reflection losses exceeding -lOdB of silica-coated CIPs are obtained in the frequency range 9.5-12.4 GHz for the absorber thickness of 2.3 mm, and the same reflection losses of uncoated CIPs reach the data in the lower frequency range for the same thickness. The enhanced microwave absorption of silica-coated CIPs can be ascribed to the combination of proper electromagnetic impedance match and the decrease of dielectric permittivity.

Microstructural and electromagnetic properties of MnO_2 coated nickel particles with submicron size

Nickel particles with submicron size are prepared by using the solvothermal method. These spheres are then coated with a layer of MnO2 using the soft chemical method. The microstructure is characterized by x-ray diffraction, transmission electron microscopy, and scanning electron microscopy. Energy x-ray dispersive spectrometry and high- resolution images show that the granular composites have a classical core/shell structure with an MnO2 superficial layer, no more than 10 nm in thickness. The hysteresis measurements indicate that these submicron-size Ni composite powders have small remanence and moderate coercivity. The electromagnetic properties of the powders measured by a vector network analyzer in a frequency range of 2-18 GHz are also reported in detail.

Effect of Mn-doping on the growth mechanism and electromagnetic properties of chrysanthemum-like ZnO nanowire clusters

Chrysanthemum-like ZnO nanowire clusters with different Mn-doping concentrations are prepared by a hydrothermal process. The microstructnre, morphology and electromagnetic properties are characterized by x-ray diffractometer high-resolution transmission electron microscopy （HRTEM）, a field emission environment scanning electron microscope （FEESEM） and a microwave vector network analyser respectively. The experimental results indicate that the as- prepared products are Mn-doped ZnO single crystalline with a hexagonal wurtzite structure, that the growth habit changes due to Mn-doping and that a good magnetic loss property is found in the Mn-doped ZnO products, and the average magnetic loss tangent tandm is up to 0.170099 for 3% Mn-doping, while the dielectric loss tangent tande is weakened, owing to the fact that ions Mn2＋ enter the crystal lattice of ZnO.

Crystal microstructure, infrared absorption, and microwave electromagnetic properties of (La_(1-x)Dy_x)_(2/3)Sr_(1/3)MnO_3

The manganite perovskite polycrystal samples of （La1-xDyx）2/3Sr1/3MnO3 （x = 0, 0.1, 0.2, 0.35, and 0.5） doped with Dy were prepared by solid state reaction in atmosphere to measure their X-ray diffraction （XRD） patterns, scanning electric microscope （SEM） images, infrared absorption spectra, and microwave electromagnetic properties. The displacement of the XRD peaks of the samples was found, and the 2θ increases from 0.05o to 0.5o. The grains of undoped La2/3Sr1/3MnO3 not only have the greatest size, but also the most regular shape. The size of the grains decreases as the Dy doping content increases from 0 to 0.5. The infrared absorption spectra of all samples were measured at room temperature. An absorption peak corresponding to the stretching vibration mode of Mn-O bonds appears within the range of 591-629 cm-1. The absorption peak shifts from a higher frequency to a lower one with the decrease of the average ionic radius of A-site. The frequency de- pendence of microwave-absorbing properties, imaginary components of the complex magnetic permeability μ＂ and dielectric permeability ε＂ for all samples was measured at room temperature from 8 to 13 GHz. The results show that the loss of microwave absorption can be attrib- uted to both the magnetic and electric losses. The increase of Dy content not only enhances the microwave absorption but also causes the displacement of the absorption peaks.

Orientation-dependent electromagnetic properties of basalt fibre/nickel core-shell heterostructures

The influence of orientation on electromagnetic properties of basalt fibre/nickel core-shell heterostructures prepared by a simple electroless plating method is investigated. For comparison, the same investigation is also performed on naked basalt fibres. For electromagnetic measurement, the directions of basalt fibre/nickel and naked basalt fibres are parallel, random and perpendicular to the direction of external electric field, termed E11 sample, random sample and E⊥ sample, respectively. Electromagnetic anisotropy can be clearly observed in the basalt fibre/nickel core-shell heterostructures, while electromagnetic properties of naked basalt fibres are unrelated to the orientation. The E⊥ basalt fibre/nickel shows the highest dielectric loss but the lowest magnetic loss, and E11 basalt fibre/nickel exhibits the highest magnetic loss but the lowest dielectric loss. The dielectric loss of E⊥ basalt fibre/nickel is several times as large as that of Eli basalt fibre/nickel, which could be attributed to the increase of polarization relaxation time as a consequence of the nanosize-confinement effect. The magnetic loss of E11 basalt fibre/nickel is even one order of magnitude higher than that of E⊥ basalt fibre/nickel, which originates mainly from the natural magnetic resonance of basalt fibre/nickel core-shell heterostructures.

Preparation of Ni/PZT Core-shell Nanoparticles and Their Electromagnetic Properties

The Ni nanoparticles coated with Pb（Zr,Ti）O3（PZT） were synthesized by a sol-gel method and in situ reaction. And their structure, oxidation resistance, and electromagnetic properties were investigated. The X-ray diffraction patterns（XRD） exhibited that a small amount of impure phase characterized to Ni（OH）2 was detected from the ammonia-treated Ni nanoparticles and the ammonia-treated Ni nanoparticles coated with PZT. After being pre-treated with aqueous ammonia, the PZT coating layer was more uniform and about 10 nm in thickness. The oxidation resistance of the ammonia-treated Ni nanoparticles coated with PZT, compared with that of the non-treated ones, was improved by about 66 ℃. The PZT shell layer prepared by in-situ reaction can greatly reduce the dielectric constant and improve the natural resonance loss at high frequency, so as to obtain the optimal impedance matching performance of the electromagnetic wave transmission.

Combustion Synthesis,Character and Electromagnetic Properties of Nano-Sized La_(0.8)Sr_(0.2)FeO_3 Perovskite

The perovskite-type nanocrystal La0.8Sr0.2FeO3 was prepared using a sol-gel auto-combustion method with citric acid as the chelating agent. The metal ions coordination compound, obtained from nitrate and citrate, underwent an auto-combustion process and voluminous ashes formed when calcining the complex in the air. Some analytical methods, which consisted of FT-IR, XRD, TEM and wave-guide, were used to characterize the gel and the final products. It was shown that metal ions and carboxyl were combined to form a homogeneous organic complex base salts in the process of gelation. The nanocrystalline had dielectric loss in the microwave frequency range of measurement.

Structural and magnetic properties of micropolycrystalline cobalt thin films fabricated by direct current magnetron sputtering

Pure cobalt(Co)thin films were fabricated by direct current magnetron sputtering,and the effects of sputtering power and pres-sure on the microstructure and electromagnetic properties of the films were investigated.As the sputtering power increases from 15 to 60 W,the Co thin films transition from an amorphous to a polycrystalline state,accompanied by an increase in the intercrystal pore width.Simultaneously,the resistivity decreases from 276 to 99μΩ·cm,coercivity increases from 162 to 293 Oe,and in-plane magnetic aniso-tropy disappears.As the sputtering pressure decreases from 1.6 to 0.2 Pa,grain size significantly increases,resistivity significantly de-creases,and the coercivity significantly increases(from 67 to 280 Oe),which can be attributed to the increase in defect width.Corres-pondingly,a quantitative model for the coercivity of Co thin films was formulated.The polycrystalline films sputtered under pressures of 0.2 and 0.4 Pa exhibit significant in-plane magnetic anisotropy,which is primarily attributable to increased microstress.

Studies of Electromagnetic Properties of MWCNTs after Electroless Plating with Co-Fe Alloy

A method of electroless plating is utilized to deposit Co-Fe alloy on the surface of multi-walled carbon nanotubes （MWCNTs）,and electromagnetic parameters of MWCNTs with and without electroless plating are discussed. The MWCNTs covered by Co-Fe is a desirable light absorbent in wide wave band by utilizing electroless plating process in experiments. Field-emission scanning electron microscope （FESEM） and field-emission transmission electron microscope （FETEM） images as well as energy dispersive spectroscopy （EDS） results are presented to show the morphology,components and electromagnetic parameters of MWCNTs. Electromagnetic properties of MWCNTs are enhanced after electroless plating observed from contrast of results be-tween MWCNTs with and without plating. In conclusion,the covering Co-Fe on the surface of MWCNTs in 2-18 GHz frequency range has better electromagnetic properties. When the material is in the 6.5 GHz electromagnetic waves,the reflection loss is up to -10 dB,and the bandwidth more than -4 dB is 5 GHz. The excellent electromagnetic properties make it probable for MWCNTs to be utilized as absorbent in electromagnetic shielding materials.

Effect of manganese addition on the microstructure and electromagnetic properties of YIG

Y3MnxFe4.85–xO12 （x=0, 0.02, 0.04, 0.06, 0.08 and 0.1） garnet ferrites （YMnIG） were prepared by conventional solid-state reaction method in air atmosphere. The effect of Mn addition on the microstructure and electromagnetic properties of YIG were investigated by means of techniques such as X-ray diffraction, scanning electron microscopey, network analyzer, hysteresigraph, magnetic balance and electron paramagnetic resonance spectrometry. Pure garnet phase of Y3Fe5O12 was identified for all the samples, except for minor YFeO3 phase appearing in the sample with x=0.06. The addition of Mn showed little influence on the dielectric constant of YIG, which varied between 14.2 and 14.5. Substituting Mnn＋ for Fen＋ in YIG decreased the total amount of Fe ions, inhibited the reduction of Fe3＋ and promoted the grain growth of garnet phase, which led to the decrease in dielectric loss and coercivity. Because the amount of Mn3＋ ions in octahedral sites in- creased with Mn concentration, the saturation magnetization showed a slight decrease firstly and then increased notably. The addition of Mn could also increase the remanence ratio of YIG ferrites by decreasing the magnetostriction constant λ111. Therefore, doping Mn into YIG fer- rites with proper quantity could improve electromagnetic properties of YIG significantly. The YMnIG ferrite with x=0.08, i.e., Y3Mn0.08 Fe4.77O12, showed the optimum electromagnetic properties： εr=14.2, tanδe=1.5×10–4, Hc=36 A/m, 4πMS=192 mT, Br/Bs=0.84, ？H=6.8 KA/m.

Physical and electromagnetic shielding properties of green carbon foam prepared from biomaterials

100%green carbon foam from the fibrous fruits of Platanus Orientalis-L(Plane)along with the tar oil as binder has been prepared using a powder molding technique.The objective was to develop a porous monolithic carbon from biomaterials with a considerable strength necessary for various physical,thermal and electromagnetic shielding applications.Fast carbonization was carried out at1000°C under the cover of Plane tree pyrolyzed seeds without using any external protective gas.For comparative analysis,some samples were mixed with5%(mass fraction)iron chloride during the molding process.Iron chloride being a graphitization catalyst and activating agent helped in increasing the specific surface area from88to294m2/g with a25%decrease in flexural strength.Thermal stability was improved due to the incorporation of more graphitic phases in the sample resulting in a little higher thermal conductivity from0.22to0.67W/(m·K).The catalytic carbon foam exhibited shielding effectiveness of more than20dB over the X-band frequency.Absorption was dominant with only8.26%?10.33%reflectance,indicating an absorption dominant shielding mechanism.The new material is quite suitable for high temperature thermal insulation being lightweight,highly porous with interconnected porous morphology most of which is preserved from the original biomaterial.

Electromagnetic properties of BaZn_2Fe_(16)O_(27)/antimony-doped tin oxide composite absorbing materials by co-precipitation method

W-type barium ferrite（Ba Zn2Fe16O27）/antimony-doped tin oxide（ATO） composite absorbing materials were synthesized by co-precipitation method, using Ba Zn2Fe16O27 prepared by traditional solid method and SnCl4·5H2O, SbCl3 as main raw materials. The structure and morphology of the composites were characterized using X-ray diffraction（XRD）, scanning electron microscopy（SEM）. The result shows that Ba Zn2Fe16O27/ATO composites were obtained by co-precipitation method, and ATO nano-particles were coated on the surface of Ba Zn2Fe16O27 ferrite. The complex permittivity and complex permeability of Ba Zn2Fe16O27/ATO composite absorbing materials at the frequency range from 2 to 18 GHz were analyzed by vector network analyzer. It is indicated that ATO has strong dielectric property and ferrite shows superior magnetic performance. The result shows that the complex permittivity and dielectric loss of the Ba Zn2Fe16O27/ATO composite absorbing materials are higher than the pure ferrite, and the complex permeability and magnetic loss are higher than the pure ferrite and the pure ATO. When the mole ratio of Ba Zn2Fe16O27/ATO is 1：2, the minimum reflection loss is about-31.14 d B at 12.4 GHz, moreover, the absorption bandwidth reaches 9.6 GHz when RL is-10 d B in the measured frequency range of Ku-band.

Preparation and electromagnetic properties of nanosized Co_(0.5)Zn_(0.5)Fe_(2)O_(4) ferrite

Nanosized Co_(0.5)Zn_(0.5)Fe_(2)O_(4) ferrite was prepared by chemical co-precipitation method.The samples were characterized by X-ray diffraction(XRD),field-emission transmission electron microscopy(FETEM),vibrating sample magnetometer(VSM)and network analyzer.TEM analysis indicates that the diameter of as-prepared powder is about 20-30 nm.The saturation magnetization of nanosized Co_(0.5)Zn_(0.5)Fe_(2)O_(4) ferrite is 74.01 mA·m^(2)·g^(−1).The complex permittivity and complex permeability of the Co-Zn ferrite were measured by vector network analyzer in the frequency range of 2.0-18.0 GHz,and the reflection loss(RL)was investigated according to the wave transmission theory.The results show that the maximum reflection loss reaches−13.7 dB at 6.8 GHz and the bandwidth of reflection loss less than−10 dB reaches 3.8 GHz.The as-prepared nanosized Co_(0.5)Zn_(0.5)Fe_(2)O_(4) ferrite can be potentially used as an excellent microwave absorber in the C-band.

Confinedly implanting Fe_(3)O_(4) nanoclusters on MoS_(2) nanosheets to tailor electromagnetic properties for excellent multi-bands microwave absorption

High efficiency microwave absorption(MA)materials with tunable electromagnetic(EM)features have been highly sought.However,it is still a challenge to achieve multi-bands absorption performance by simple optimizing the chemical composition of MA materials.Herein,a simple solvothermal method was used to embed magnetic Fe_(3)O_(4) nanodusters on MoS2 nanosheets,in which magnetic nanodusters weme quantitatively customized More importantly,the MA frequency and MA properties of the material are highly tailored,and multi-bands absorption is achieved.The minimum reflection loss(RL)of Fe_(3)O_(4)/MoS_(2) composite reaches-87.24 dB and is about 4 times more than pure MoS_(2) nanosheets.The effective ab-sorption bandwidth reaches 5.52 GHz(≤-10 dB).These desirable properties result from the introduction of appropriate magnetic Fe_(3)O_(4) nanoclusters,which provide optimal synegistic effect of dielectric and magnetic losses.This result provides a feasible idea for designing high efficiency MA materials with tunable EM features in the future.

Structures and Electromagnetic Properties of Electroless Ni-Co-P Coatings Before and After Annealing

Ni-Co-P coatings containing Ni 46.13 wt%,Co 45.05 wt%and P 8.82 wt%were electroless-plated on carbon steel substrates and annealed at a series of temperatures.The structure of as-plated coatings was amorphous,and crystallization took place around 623 K.By annealing the coatings at 823 K for 60 min,stable face-centered cubic Ni(Co) and Ni_3P phase were obtained.Electrical resistivity decreased remarkably by increasing the annealing temperature.Both saturation magnetization and coercivity attained their highest values when the coatings were annealed at 723 K.Totally,the Ni-Co-P coatings exhibited semi-hard magnetic characteristics and could be used as magnetic recording materials after annealing.

Electromagnetic properties of electro-textiles for wearable antennas applications

Wearable,textile-based antennas get more and more attention for body-centric communications because it could be easily worn on body and integrated into clothes.Electro-textiles(e-textiles)are used as antenna patch and ground plane.The electromagnetic properties of the textiles play important roles in antenna design and performance.This paper focuses on the study of the electromagnetic properties of e-textiles for wearable antennas applications and mainly discusses the electromagnetic properties of e-textile cell and the influences of different woven densities and different e-textile materials to antenna performances.Simulation and measurement results show that if the e-textiles adopt woven pattern,then when the distance between two conductive fibers is within 2 mm,the e-textiles could be regarded as metal plane to design antennas.In addition,the results show that metalplated woven fabric could be used as metal plane to design antennas,while non-woven fabric shows distinct differences.

Precise in-situ characterization and cross-validation of the electromagnetic properties of a switched reluctance motor

The electrical-magnetic characteristics of a Switched Reluctance Motor(SRM)exhibit highly nonlinear relationshipwith respect to the rotor position and excitation current,which poses challenges for both precise static measurements and exact calculation of these properties in real-time control.To guarantee that an in-lab test result can be used in the application,firstly a measurementmethod is proposed to characterize the SRM's electromagnetic properties such as the flux linkage,magnetic co-energy,phase inductance and electromagnetic torque on the basis of an installed SRM control circuitry and half-bridge power converter.By this means the characterization process is equivalent to the online observation in its results.Secondly,a theoreticalmodel is built to discriminate the physical meaning between the incremental inductance and the phase inductance,which is the origin of other relevant parameters.This helps to guide the correct utilization of the characterization result.Thirdly an in-situ cross-validation experimentation according to the magnetizing and demagnetizing status measurement verifies the feasibilities and accuracy of the proposed inductance measuring method,which avoid a dubious FEM-based comparison between the numerical calculation and experimental results.Cross-validation experiment shows that the proposed in-situ characterization scheme obtains an accurate full-range electromagnetic properties.The proposed methodology breaks the barrier between the in-lab measurement and on-line utilization of the SRM parameters,highlighting the merits that it completely includes the in-situ factors and replicates the operational scenario without the need of specifically designed instrumentation,which is especially suitable for rapid field characterization for high power motors.