Influence of absorbent on electromagnetic wave absorbing property of porous concrete

Influences of ferrite content and iron ore powder content on electromagnetic wave absorbing property of porous concrete are studied.The radar cross section(RSC)of samples was tested in a microwave anechoic chamber.Results show that the optimum content of ferrite is 15%,and the minimum,maximum and average reflectivity of the sample is-46.60 dB,-10.84 dB and-23.75 dB,respectively.And the sample's improved bandwidth is 8.2 GHz.The optimum content of iron ore powder is 20%,and the minimum,maximum and average reflectivity of the sample is-34.69 dB,-9.25 dB and-20.69 dB,respectively.And the sample's improved bandwidth is 6 GHz.In conclusion,appropriate ferrite and iron ore powder can improve wave absorbing property and widen wave absorption bandwidth of porous concrete.

Enhanced microwave absorption property of silver decorated biomass ordered porous carbon composite materials with frequency selective surface incorporation

Porous carbon(PC)is a promising electromagnetic(EM)wave absorbing material thanks to its light weight,large specific surface area as well as good dissipating capacity.To further improve its microwave absorbing performance,silver coated porous carbon(Ag@PC)is synthesized by one-step hydro-thermal synthesis process making use of fir as a biomass formwork.Phase compositions,morphological structure,and microwave absorption capability of the Ag@PC has been explored.Research results show that the metallic Ag was successfully reduced and the particles are evenly distributed inward the pores of the carbon formwork,which accelerates graphitization process of the amorphous carbon.The Ag@PC composite without adding polyvinyl pyrrolidone(PVP)exhibits higher dielectric constant and better EM wave dissipating capability.This is because the larger particles of Ag give rise to higher electric conductivity.After combing with frequency selective surface(FSS),the EM wave absorbing performance is further improved and the frequency region below-10 d B is located in8.20-11.75 GHz,and the minimal reflection loss value is-22.5 dB.This work indicates that incorporating metallic Ag particles and FSS provides a valid way to strengthen EM wave absorbing capacity of PC material.

Studies on the Absorption of NO_2 by Polyethylene Glycol and the Oxidizing Properties of the Resulting Absorbent Product

PEG (Polyethylene glycol average molecular weight 300) is used as absorbent of NO2. The absorption efficiency is found to reach up to 97%. The absorbing product, PEG NO2, can be used to cleave benzyl ethers mildly and selectively to benzaldehyde and corresponding fatty alcohols, showing that PEG is a valuable oxidizing agent of benzyl ethers. As a carrier of NO2.PEG can be recovered and utilized repeatedly after the oxidation.

Magnetic and microwave absorbing properties of M-type barium ferrite/graphene oxide composite microwave absorber

In order to improve the absorbing properties of M- type barium ferrite absorbing materials, M-type barium ferrite/graphene oxide composites with different graphene oxide contents were synthesized by the sol-gel autocombustion method. X-ray diffraction （XRD）, a scanning electronic microscopy （ SEM ）, a physical properties measurement system （PPMS-9）, and a vector network analyzer were used to analyze their structure, surface morphology, magnetic and absorbing properties, respectively. The results show that the absorbing band of the composite absorbing material is widened and the absorbing strength is increased compared with the pure M-type barium ferrite. The sample with the content of doped graphene oxide of 3% has the minimum reflectivity at 10 to 18 GHz frequencies. Hence, the doped graphene oxide effectively improves the absorbing properties of M-type barium ferrite.

A thin radar-infrared stealth-compatible structure:Design,fabrication,and characterization

A thin radar-infrared stealth-compatible structure with reflectivity below -10 dB in the whole radar X wave band and infrared emissivity less than 0.3 in the infrared region of 8μm-14 μm is reported. The designed stealth-compatible structure consists of metallic frequency selective surface （MFSS）, resistive frequency selective surface （RFSS）, and metal backing from the top down, and it is only 2. l-mm thick. The MFSS is made up of some divided low infrared emissivity metal copper films, and the RFSS consists of a capacitive array of square resistive patches. They are placed close together, working as an admittance sheet because of a mutual influence between them, and the equivalent admittance sheet greatly reduces the thickness of the whole structure. The proposed stealth-compatible structure is verified both by simulations and by experimental results. These results indicate that our proposed stealth-compatible structure has potential applications in stealth fields.

Electromagnetic and microwave absorbing properties of FeCoB powder composites

The electromagnetic and microwave absorbing properties of FeCoB powder composites prepared by sin- gle-roller melt-spinning and mechanical milling processes were investigated in this paper. The result indicates that the flake-like powders are obtained. As milling time increases, the flake-like powder particles tend to agglomerate, causing the flake-like powders decrease gradually. The milling time plays an important role in the electromagnetic parameters which relates to the shape and size of the powder particles. The calculation shows that the sample milled for 6 h could achieve an optimal reflection loss of -11.5 dB at 5.8 GHz, with mass fraction of 83 % and a matching thickness of 1.8 mm. The result also indicates that the microwave absorbing properties of the FeCoB powder composites are adjustable by changing their thickness, and can be applied as a thinner microwave absorbing material in the range of 2-8 GHz.

The absorbing properties of Fe_(73.5) Cu_1 Nb_3Si_(13.5)B_9 amorphous powder/S-glass fiber-reinforced epoxy composite panels

Fe73.5Cu1Nb3Si13.5B9 （or FeCuNbSiB） powder/ S-glass fiber-reinforced epoxy composite panels were pre- pared by mold pressing method. Metallographic analysis shows that the amorphous powders are evenly distributed between the layers of S-glass fibers. The effects of the Fe- CuNbSiB powder mass fraction on the complex permittivity, complex permeability, and microwave absorption of the composite panels have been studied in the frequency range of 2.6-18.0 GHz. The complex permittivity of the composite panels with different mass fractions of the FeCuNbSiB powders shows several peaks in the 2.6-18.0 GHz fre- quency range. The complex permeability of the composites decreases with the increasing frequency in the frequency range of 8-18 GHz. The composite with FeCuNbSiB/epoxy mass ratio of 2.5：1.0 has excellent microwave absorption properties of a minimum reflection loss value -30.5 dB at 10.93 GHz for a thickness of 2 mm. A reflection loss exceeding -10 dB can be obtained in a broad frequency range of 3.2-18.0 GHz with a thickness of 1.15-5.00 mm. For the FeCuNbSiB composites, the magnetic loss is the dominant term for microwave absorption. The FeCuNbSiB powders are a possible candidate for high-performance microwave absorption filler.

Synthesis of flowerlike nickel particles and their microwave absorbing properties

Two kinds of nickel particles with flower-like struc~＇es assembled with a number of nano-flakes were synthesized and the relationship of their morphology and microwave absorbing properties was studied. The electromagnetic parameters of these flower-like Ni were measured with vector network analyzer at 2-18 GHz frequency and the reflection losses （RL） with different sample thicknesses were calculated. The results indicate that the flower-like nickel-wax composites with the sample thickness less than 2 mm show excellent absorbing ability. This result is expected to play a guiding role in the preparation of the highly efficient absorber.

Microwave Absorbing Performance of RE-Fe Based Alloys

REI3Fes4Cr3（RE=Ce, Pr, Tb, Er） and Pr13_XFes4Cr3Ti（x=0, 2, 4, 6） alloy powders were prepared by are smelting method and high energy ball milling technique. The phase structure and the morphology of the alloy powders were investigated by X-ray diffraction （XRD） and scanning electron microscopy （SEM）, and their microwave absorbing properties were determined by a vector network analyzer. The results show that the alloys with light rare earths （Ce, Pr） have good low frequency absorbing property and those with heavy rare earths （Tb, Er） exhibit an improved high frequency absorbing property. The minimum refleetivity at the absorbing peak frequency of RE,FeuCr3（RE=Ce, Pr, Tb, Er） are -9.49 dB at 5.76 GHz, -22.38 dB at 7.92 GHz, -18.52 dB at 11.68 GHz and -17.59 dB at 10.24 GHz, respectively. The absorbing bandwidth under -10 dB of the Pr13FesaCr3 powder was widened from 1.91 GI-Iz to 3.89 GHz by adding 2% Ti, but the reflectivity of the alloy was increased from -22.38 dB to -14.91 riB.

Preparation of new sunscreen materials Ce_(1-x)Zn_xO_(2-x) via solid-state reaction at room temperature and study on their properties

Superfine cerium-zinc oxides Ce1-xZnxO2-x with x = 0, 0.1, 0.3, 0.5, and 1.0 were obtained by grinding Ce（SO4）2·4H2O, ZnSO4·7H2O and NH4HCO3 under the condition of surfactant PEG-400 being present at room temperature, washing the mixture with water to remove soluble inorganic salts, drying at 80°C, and calcining.The precursor and its calcined samples were characterized using thermogravimetry and differential thermal analyses（TG/DTA）, UV-vis absorption spectroscopy, X-ray powder diffraction（XRD）, and scanning electron microscopy（SEM）.The results showed that superfine Ce1-xZnxO2-x behaved as an excellent UV-shielding material.The ZnO-doped CeO2 can facilitate the formation of crystalline state CeO2.The catalytic ability of products used in air oxidation of castor oil was investigated.The results showed that the catalytic abilities of products decreased with increasing zinc amount.

Mossbauer spectroscopy studies on the particle size distribution effect of Fe–B–P amorphous alloy on the microwave absorption properties

An Fe-based nanocrystalline alloy powder is important for application in microwave absorption,and the particle size has a critical impact on the electromagnetic microwave parameters.Therefore,it is necessary to study further the effects of the particle size on such parameters and improve the microwave absorption performance of Febased nanocrystalline powers.In this study,Fe-B-P particles were prepared through a synthetic approach consisting of an aqueous chemical reduction and a ball milling treatment.We investigated the effects of ball milling on the microstructure and electromagnetic properties of Fe-B-P particles.The experimental results indicate that the Fe-B-P particles synthesized through an aqueous chemical reduction are amorphous spheres.Fe-B-P particles with an original particle size of 200-1200 nm can be milled into an irregular shape with the size reduced to\500 nm after 0.5 h of ball milling,and subsequently,the particles become smaller with increases in the milling time,with traces of Fe2O3 generated on the particle surface.The results of the Mo¨ssbauer spectra show that a portion of the small particles demonstrate a superparamagnetic property.The volume proportions of the superparamagnetic component increase from 13.1 to 15.8%as the treatment time increases.We measured the permittivity and permeability spectra of Fe-B-P particles within the frequency range of 2-18 GHz.The reflection loss(RL)is-10 dB for an absorber thickness of 1.7-5.0 mm.The RL is-20 dB for an absorber thickness of 1.9-2.7 mm.The microwave absorption properties of samples with the same thickness are improved with an increase in the treatment time and are shifted to a higher frequency,which will broaden the bandwidth of the absorption as well.

Bridging the terahertz near-field and far-field observations of liquid crystal based metamaterial absorbers

Metamaterial-based absorbers play a significant role in applications ranging from energy harvesting and thermal emitters to sensors and imaging devices.The middle dielectric layer of conventional metamaterial absorbers has always been solid.Researchers could not detect the near field distribution in this layer or utilize it effectively.Here,we use anisotropic liquid crystal as the dielectric layer to realize electrically fast tunable terahertz metamaterial absorbers.We demonstrate strong,position-dependent terahertz near-field enhancement with sub-wavelength resolution inside the metamaterial absorber.We measure the terahertz far-field absorption as the driving voltage increases.By combining experimental results with liquid crystal simulations,we verify the near-field distribution in the middle layer indirectly and bridge the nearfield and far-field observations.Our work opens new opportunities for creating high-performance,fast,tunable,terahertz metamaterial devices that can be applied in biological imaging and sensing.

Preparation and Microwave Absorbing Properties of Double-layer Fine Iron Tailings Cementitious Materials

To develop the microwave absorbing(MA)properties of cementitious material mixed with mine solid waste,the iron tailings cementitious microwave absorbing materials were prepared.The iron tailings was treated into different particle sizes by planetary ball mill,and the physicochemical properties of iron tailings were tested by laser particle size analyzer and scanning electron microscope(SEM).The electromagnetic parameters of iron tailings cementitious materials were characterized by a vector network analyzer and simulated MA properties,and the MA properties of iron tailings-cement composite system with steel fiber as absorber was studied.Based on the design of the single-layer structure,optimum mix ratio and thickness configuration method of double-layer structure were further studied,meanwhile,the mechanical properties and engineering application were analyzed and discussed.The results show that the particle size of iron tailings can afiect its electromagnetic behavior in cementitious materials,and the smaller particles lead the increase of demagnetisation efiect induced by domain wall motion and achieve better microwave absorbing properties in cementitious materials.When the thickness of matching layer and absorbing layer is 5 mm,the optimized microwave absorbing properties of C1/C3 double-layer cementitious material can obtain optimal RL value of-27.61 dB and efiective absorbing bandwidth of 0.97 GHz,which attributes to the synergistic efiect of impedance matching and attenuation characteristics.The double-layer microwave absorbing materials obtain excellent absorbing properties and show great design flexibility and diversity,which can be used as a suitable candidate for the preparation of favorable microwave absorbing cementitious materials.

Study of Microwave Absorbing Performances of Nanometer Fe-Al Solid solution

In this paper,Fe-Al solid solution was prepared by mechanical alloying technology,and Fe-Al powder was dispersed into unsaturated polyester (UP) with different contents as absorber to form mixture Fe-Al-UP.The results indicate that the alloying process is almost accomplished and most of the particles are nanometer.Meanwhile,the microwave absorbability of Fe-Al-UP samples in frequency from 0.3 MHz to 1.5 GHz was studied.The results indicate that the more the absorber,the better the absorbing property.The absorbing property of Fe-50Al-UP was slightly higher than Fe-28Al-UP.

Electroless plating of carbon nanotubes and their millimeter-wave absorbing properties

A method of electroless plating was utilized to deposit Cu, Ni, Co, Ag on the surface of carbon nanotubes （CNTs） respectively, in order to prepare millimeter-wave absorbing materials. Field emission scanning electron microscope （FE-SEM） and energy dispersive spectrometer （EDS） were used to observe morphologies and chemical compositions of the samples respectively. Millime- ter-wave radiometer imaging detection was employed to measure the absorbing properties of the sam- ples. FE-SEM and EDS results demonstrate the effectiveness of successful metal deposition. The re- suits of millimeter-wave radiometer imaging detection reveal that the millimeter-wave absorbing properties of electroless-silver plating are better than other kinds of samples.

Physical-Chemical and Pharmacological Research on New Lignin Enterosorbent

The technology on obtaining enterosorbent from local feedstock--hydrolyzed lignin of cotton seed hulls named Zerotox was developed. The purpose of this research is to conduct a complex study on its physical-chemical and pharmacological properties. Samples of cotton hydrolyzed lignin based enterosorbent Zerotox were investigated, wood hydrolyzed lignin based enterosorbent Polifepan （Russia） was used as a comparison drug. The technology of new medical enterosorbent Zerotox, based on cotton hydrolyzed lignin, has been developed with its physical-chemical and pharmacological characteristics being researched. Comparative research on adsorbing capacity of sorbent Zerotox （80 mg/g） and its analogue--Polipefan （55 mg/g）, which is obtained from wood hydrolyzed lignin, has displayed advantages of the new sorbent. IR-spectroscopy research on lignin sorbent Zerotox has shown presence of oxygen-containing functional groups which determine its high absorbing capacity due to its chemisorption. Atomic-adsorptive method has proved high absorbing capacity of the sorbent towards heavy metals ions. Acute and chronic toxicity and antidiarrheal activity of enterosorbent Zerotox have also been studied.

Rare Earth Dragons

The invention covers the process for preparing an oxide complex that can absorb and release oxygen. The covered procedures include:preparation of CeO2, ZrO2 and HfO2 as raw material; preparation of the complex oxide with the raw material by employing heating and deoxidation method;and the process for re-heating and oxidizing the deoxidized complex oxide.

Infrared emissivity and microwave absorbing property of epoxy-polyurethane/annealed carbonyl iron composites coatings

The microwave absorption property and infrared emissivity have been investigated for the single-layer coating made of the epoxy-polyurethane resin and carbonyl iron powders with variation of annealing treatment. Microwave-absorbing property was investigated by measuring the complex permittivity and complex permeability of the absorber in the frequency range from 2 to 18 GHz. Infrared emissivity value was measured using IR-2 Infrared Emissometer in the wavelength range of 8-14 μm. After annealing, the Fe （110） peak became sharp, and the crystallization improved significantly. Annealing treatment could reduce the sttrface energy of powders, improve compatibility between fillers and adhesives, and result in increase of the density of the coating. The lowest value of infrared emissivity （0.419） was obtained from the coating made of the carbonyl iron powder annealed at 700℃ for 1 h. With the variation of the annealing temperature, the magnetic and dielectric properties of the carbonyl iron particle were changed. The maximum reflection loss decreased and the matching frequency shifted to lower frequency with increasing the annealing temperature of carbonyl iron particles, which coincided with the variation of the complex permeability and permittivity according to the annealing temperature. Magnetic loss factor and dielectric loss factor of carbonyl iron particles were improved with increasing the annealing temperature in the 2-18 GHz range.

Effects of Particle Sizes on the Electromagnetic Property of Flaky FeSi Composites

Flaky FeSi absorbents with different size ranges were fabricated by sintering after mechanical milling process. X-ray diffraction （XRD） was used to analyze the particle crystal grain structure. The complex permittivity and permeability of FeSi/paraffin composites were measured in frequency of 2-12 GHz using a vector network analyzer, and the DC electric conductivity was measured by the standard four-point contact method, then microwave reflection loss （RL） and shielding effectiveness （SE） were calculated. It was obtained that c^-Fe appeared in the super-lattice diffraction peaks in XRD pattern. As the particles size decreased, the permittivity decreased due to the inferior microwave electrical conductivity and dielectric loss tangent, while the permeability increased due to the decrease of diameter-thickness ratio, which could be demonstrated in the comparison between the experiment and calculation results. When thickness is 1 mm, the composites with the smallest FeSi particles addition had a better absorbing property for the better impedance matching characteristic, and the minimum RL was -7.9 dB at 4.6 GHz. While the composites with larger FeSi particles addition had an excellent shielding property due to the higher permittivity, the SE value ranged from 15 dB to 30 dB at the frequency band.

Preparation of hollow ceramic microspheres absorbent based on self-reactive quenching technology

A1 ＋ BaO2 ＋ Fe2O3 ＋ sucrose and O2 as reaction system and feeding gas, respectively, are used to prepare hollow multiphase ceramic microspheres （HMCMs） absorbent based on self-reactive quenching technology. The morphologies, particle size distribution, hollow structure and phase compositions were characterized by scanning electron microscope （SEM）, X-ray diffraction （XRD） and size analysis. The results show that the quenching products possess high sphere-forming rate, and most of them are hollow structures. Owing to the self-burst, the particle size is between 40 and 70 μm. The phase compositions contain Al2O3, Fe3O4, Fe2O3, Ba2Fe14O22, BaO2 and BaFe4O7. The microwave absorbing tests show that the lowest reflectivity of HMCMs is -19 dB. The frequency bands less than -10 dB are from 13.0 to 15.8 GHz. The reasons for HMCMs possessing good microwave absorbing properties may be their magnetic and electrical properties as well as special hollow structure.