Tuning magneto-dielectric properties of Co_(2)Z ferrites via Gd doping for high-frequency applications

Magneto-dielectric properties of Co_(2)Z ferrite materials are tuned via Gd doping for applications in high-frequency antennas and filters in the present work.Ba_(3)Co_(2)Fe_(24-x)Gd_(x)O_(41)(x=0.00,0.05,0.10,0.15,and 0.20)materials are successfully prepared by using solid-state method at 925℃for 4 h with 2.5-wt%Bi_(2)O_(3)sintering aids.The content of Gd^(3+)ion can affect micromorphology,grain size,bulk density,and magneto-dielectric properties of the ferrite.With Gd^(3+)ion content increasing,saturation magnetization(Ms)first increases and then decreases.The maximum value of Ms is 44.86 emu/g at x=0.15.Additionally,sites occupied by Gd^(3+)ions can change magnetic anisotropy constant of the ferrite.Magnetocrystalline anisotropy constant(K_1)is derived from initial magnetization curve,and found to be related to spin-orbit coupling and intersublattice interactions between metal ions.The real part of magnetic permeability(μ′)and real part of dielectric permittivity(ε′)are measured in a frequency range of 10 MHz-1 GHz.When x=0.15,material has excellent magneto-dielectric properties(μ′≈12.2 andε′≈17.61),low magnetic loss(tanδμ≈0.03 at 500 MHz),and dielectric loss(tanδε≈0.04 at 500 MHz).The results show that Gd-doped Co_(2)Z ferrite has broad application prospects in multilayer filters and high-frequency antennas.

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.

Thermodynamics and kinetics of carbothermal reduction of zinc ferrite by microwave heating

The kinetics of carbon reduction of ZnFe2O4 in the temperature range of 550-950 °C was investigated in a microwave tank-type reactor. The mechanism of formation of ZnO and Fe3O4/FeO by the decomposition of ZnFe2O4 was detailed using the equilibrium calculations and thermodynamics analysis by HSC chemistry software 6.0. In addition, the effects of decomposition temperature, the C/ZnFe2O4 ratio, the particle size and the microwave power were assessed on the kinetics of decomposition. Zn recovery as high as 97.93%could be achieved at a decomposition temperature of 750 °C with C/ZnFe2O4 ratio of 1：3, particle size of 61-74 μm and microwave power of 1200 W. The kinetics of decomposition was tested with different kinetic models and carbon gasification control mechanism was identified to be the appropriate mechanism. The activation energy for the carbon gasification reaction was estimated to be 38.21 kJ/mol.

A review of microwave-induced thermoacoustic imaging:Excitation source,data acquisition system and biomedical applications

Microwave-induced thermoacoustic imaging(TAI)is a noninvasive modality based on the differences in microwave absorption of various biological tissues.TAI has been extensively researched in recent years,and several studies have revealed that TAI possesses advantages such as high resolution,high contrast,high imaging depth and fast imaging speed.In this paper,we reviewed the development of the TAI technique,its excitation source,data acquisition system and biomedical applications.It is believed that TAI has great potential applications in biomedical research and clinical study.

STUDY AND APPLICATION OF THE AERIAL PASSIVE MICROWAVE REMOTE SENSING

Ⅰ. Introduction Over the past two decades, microwave remote sensing has evolved into a focal point in the remote sensing area. This is due to the fact that in microwave band, we can acquire physical parameters about ocean, terrain and atmosphere on all weather condition. Research and application work about the aerial passive micro wave remote sensors has been done at Changchun Institute of Geography since 1973, under the unitary planning of Academia Sinica. Microwave radiometers of six freqency bands have been developed. Numerous remote sensing experiments were carried out, and large amount of scientific data were accumulated. Recently, theoretical models have

Magnetic Nano Cobalt Ferrite Catalyzed Synthesis of 4H-Pyrano[3,2-h]quinoline Derivatives under Microwave Irradiation

A microwave irradiated magnetically separable nano cobalt ferrite catalyzed green method for the synthesis of 4-phenyl-4H-pyrano[3,2-h]quinolin-2-amine and 2-amino-4-phenyl-4H-pyrano[3,2-h] quinoline-3-carbonitrile derivatives through cyclization of aromatic aldehyde, acetonitrile/malononitrile and 8-hydoxyquinoline is developed and presented in this paper. The cubic magnetic cobalt ferrite nano particles were synthesized by sol-gel citrate precursor method and characterized by FT-IR, XRD, SEM and TEM techniques and the structures of the synthesized pyranoquinoline derivatives were assigned by IR, MASS and 1H NMR techniques. The reaction is carried out in a domestic microwave oven with a heat-resistant microwave safe glass container with a lid.

Effect of acupoint application combined with microwave treatment on the intestine barrier functional disturbance of moderately severe acute pancreatitis

Objective: To explore and analyze the effect of acupoint application combined with microwave treatment on the intestinal barrier dysfunction with moderately severe acute pancreatitis. Methods: A convenient sample of 90 moderately severe acute pancreatitis was selected from March 2017 to December 2017 in the comprehensive hospital with third grade in Tianjin. The patients were divided into group A (acupoint application combined with microwave treatment), group B (acupoint application) and group C (routine nursing). Thirty patients were included in each group. This study need to get the informed consent of the patients. Acupoint application combined with microwave treatment was used, basing on routine nursing measures in group A. Acupoint application was used by the same way and the same traditional Chinese medicine ,basing on routine nursing measures in group B. Routine nursing used in group C. C-reactive protein and the score of intestinal function were measured on 3 th day, 7 th day and 10 th day, after intervention. To record the effective ratio of the treatment after 10 days of intervention. Results: There are significant statistical difference among the three group after intervention (P < 0.05). Conclusion: In some way, acupoint application combined with microwave treatment are able to decrease the time about the recovery of intestinal barrier dysfunction in moderately severe acute pancreatitis and to alleviate the suffering of patients.

Templated synthesis of highly ordered mesoporous cobalt ferrite and its microwave absorption properties

Based on the nanocasting strategy, highly ordered mesoporous CoFe2O4 is synthesized via the ＇two-solvent＇ im- pregnation method using a mesoporous SBA-15 template. An ordered two-dimensional （P6mm） structure is preserved for the CoFe2O4/SBA-15 composite after the nanocasting. After the SBA-15 template is dissolved by NaOH solution, a mesoporous structure composed of aligned nanoparticles can be obtained, and the P6mm structure of the parent SBA-15 is preserved. With a high specific surface area （above 90 m2/g） and ferromagnetic behavior, the obtained material shows potential in light weight microwave absorption application. The minimum reflection loss （RL） can reach -18 dB at about 16 GHz with a thickness of 2 mm and the corresponding absorption bandwidth is 4.5 GHz.

Synthesis and Microwave Electromagnetic Properties of M-type Hexagonal FerriteBaTiCoFe_(10)O_(19)

An M-type hexagonal ferrite BaTiCoFe10 O19 was prepared by solid phase reaction by a partial 2Fe3+→Ti4+ Co2+ substitution. The morphology observation and phase identification of BaTiCoFe10O19 were carried out by SEM and XRD, and its X-ray powder diffraction data was reported in this paper for the first time. Further, the microwave electromagnetic properties of BaTiCoFe10O19 were measured and discussed.

Effect of Sintering Temperature on Microwave Absorbing Behaviour of Mn-Zn Ferrite

The microwave absorbing behaviour of Mn-Zn ferrite sintered at 1100,1200,1300,1400 and 1500℃ has been investigated.The phase constitution of the ferrite was analyzed by X-ray diffraction.The results show that the ferrite sintered at 1 500℃ has better microwave absorbing prop- erty than those prepared at other temperatures,due to the increase of turbulent loss generated by the formation of excessive Fe^(2+) in deoxidizing of Fe_2O_3 at high temperatures.

MICROWAVE RADIOMETER AND ITS APPLICATION TO SNOW MEASUREMENT

The microwave radiactivproperty of snow is studied using self-developed three band microwave radiometers. Experiments were carried out repeatedly from 1986 to 1989 in Northeast China The relation between brightness temperature and observation angle was obtained with both vertical and horizontal polarizations. The curves corresponding brightness temperature and snow depth were also drawn out for different frequency bands. The results demonstrate the application potential of the multifrequency microwave radiometer in this area.

A Multifunctional Microwave Plasma Reaction Apparatus and its Applications

A multifunctional apparatus for microwave plasma reaction has been set up, which can be used in the fields such as Chemical synthesis, surface modification, and heterogeneous catalysis. This apparatus has laid an experimental foundation for new methods, new technologies, and new train of thoughts to be explored.

Fabrication and performance optimization of Mn-Zn ferrite/EP composites as microwave absorbing materials

Magnesium-substituted Mn0.8Zn0.2Fe2O4 ferrite is synthesized by the sol–gel combustion method using citrate acid as the complex agent. The electromagnetic absorbing behaviors of ferrite/polymer coatings fabricated by dispersing Mn–Zn ferrite into epoxy resin （EP） are studied. The microstructure and morphology are characterized by X-ray diffraction and scanning electron microscope. Complex permittivity, complex permeability, and reflection loss of ferrite/EP composite coating are investigated in a low frequency range. It is found that the prepared ferrite particles are traditional cubic spinel ferrite particles with an average size of 200 nm. The results reveal that the electromagnetic microwave absorbing properties are significantly influenced by the weight ratio of ferrite to polymer. The composites with a weight ratio of ferrite/polymer being 3：20 have a maximum reflection loss of –16 dB and wide absorbing band. Thus, the Mn–Zn ferrite is the potential candidate in electromagnetic absorbing application in the low frequency range （10 MHz–1 GHz）.

Characterization and Electromagnetic Studies on NiZn and NiCuZn Ferrites Prepared by Microwave Sintering Technique

The low-temperature sintered NiZn and NiCuZn ferrites with the composition of Ni0.40Zn0.60Fe2O4 and Ni0.35Cu0.05Zn0.60 Fe2O4 were respectively synthesized by the microwave sintering method. These powders were calcined, compacted and sintered at 950℃ for 30 min. X-ray diffraction (XRD) patterns of the samples indicate the formation of single-phase cubic spinel structure. The grain size was estimated from SEM images which increase with CuO addition. The X-ray density is higher than the bulk density in both the ferrites. The temperature variation of the initial permeability of these samples was carried out from 30℃ to 250℃. The NiCuZn ferrite had higher initial permeability than that of the NiZn ferrite, which could be attributed to the microstructure. Saturation magnetization increases from 40 emug/g (NiZn) to 47 emug/g (NiCuZn). The dielectric constant and dielectric loss tangent of NiZn and NiCuZn ferrite samples decreases with increase in frequency exhibiting normal ferrimagnetic behavior. The NiCuZn ferrite had better electro- magnetic properties than the NiZn ferrite.

Microstructure and Microwave Absorption Properties of Y-Substituted Ni-Zn Ferrites

The Yttrium ions substituted Ni-Zn ferrites powders were prepared using a sol-gel technique. The crystal structure, magnetic properties and microwave absorption properties of the Ni-Zn ferrites powders were studied by X-ray diffraction, vibrating sample magnetometer and vector network analyzer. The results show that the microwave absorption properties of the Ni-Zn ferrites can be improved effectively with the substitution of Y ions. The minimum reflection loss of the Yttrium ions substituted Ni-Zn powder reaches –34.8 dB, with the –20 dB bandwidth over 2 GHz. The Yttrium substitution can improve microwave absorption properties of Ni-Zn ferrite due to smaller grain dimension and the higher specific

Synthesis of nitrogen-doped reduced graphene oxide/magnesium ferrite/polyaniline composite aerogel as a lightweight,broadband and efficient microwave absorber

The fabrication of graphene-based microwave absorbing materials with low density,small filling ratio,broad bandwidth and strong absorption remains a huge challenge.In this work,nitrogen-doped reduced graphene oxide/magnesium ferrite/polyaniline(NRGO/MgFe_(2)O_(4)/PANI)composite aerogel was synthesized by a three-step method of solvothermal reaction,in situ chemical oxidation polymerization and hydrothermal self-assembly.The results showed that the obtained aerogels had a unique three-dimensional(3D)porous network structure and low bulk density(11.1-13.0 mg cm^(−3)).It was worth noting that in the NRGO/MgFe_(2)O_(4)/PANI ternary composite aerogel,MgFe_(2)O_(4)coated with a thin PANI layer was anchored on the surface of NRGO sheets.Furthermore,the NRGO/MgFe_(2)O_(4)/PANI ternary composite aerogel showed much better microwave absorbing capacity compared with pure NRGO aerogel and NRGO/MgFe_(2)O_(4)binary composite aerogel.When the filling ratio was as low as 11.5 wt.%,the obtained ternary composite aerogel exhibited the maximum effective absorption bandwidth of 7.0 GHz at a matching thickness of 2.1 mm,and the minimum reflection loss of-42.9 dB at a thickness of 3.57 mm.Additionally,the prob-able microwave dissipation mechanism was also elucidated.It was believed that this study would pave the way for the construction of 3D graphene-based composites as lightweight,broadband and efficient microwave absorbents.

Achieving Ultra-Broad Microwave Absorption Bandwidth Around Millimeter-Wave Atmospheric Window Through an Intentional Manipulation on Multi-Magnetic Resonance Behavior

The utilization of electromagnetic waves is rapidly advancing into the millimeter-wave frequency range,posing increasingly severe challenges in terms of electromagnetic pollution prevention and radar stealth.However,existing millimeter-wave absorbers are still inadequate in addressing these issues due to their monotonous magnetic resonance pattern.In this work,rare-earth La^(3+)and non-magnetic Zr^(4+)ions are simultaneously incorporated into M-type barium ferrite(BaM)to intentionally manipulate the multi-magnetic resonance behavior.By leveraging the contrary impact of La^(3+)and Zr^(4+)ions on magnetocrystalline anisotropy field,the restrictive relationship between intensity and frequency of the multi-magnetic resonance is successfully eliminated.The magnetic resonance peak-differentiating and imitating results confirm that significant multi-magnetic resonance phenomenon emerges around 35 GHz due to the reinforced exchange coupling effect between Fe^(3+)and Fe^(2+)ions.Additionally,Mosbauer spectra analysis,first-principle calculations,and least square fitting collectively identify that additional La^(3+)doping leads to a profound rearrangement of Zr^(4+)occupation and thus makes the portion of polarization/conduction loss increase gradually.As a consequence,the La^(3+)-Zr^(4+)co-doped BaM achieves an ultra-broad bandwidth of 12.5+GHz covering from 27.5 to 40+GHz,which holds remarkable potential for millimeter-wave absorbers around the atmospheric window of 35 GHz.

Analysis of cerium substitution in Co-Sr based spinel ferrites for high frequency application

Spinel ferrites exhibit exceptional magnetic properties,making them a distinctive class of magnetic materials.The sol-gel technique was utilized for the synthesis of spinel ferrites with the chemical formula Co_(0.6)Sr_(0.4)Ce_(x)Fe_(2-x)O_(4). Following that,a comprehensive X-ray diffraction analysis unveiled the crystalline cubic structure of the synthesized materials.Through the utilization of the M-H loop approach,the ferromagnetic attributes of ferrites were assessed,and the assimilation of rare earth elements led to substantial enhancements in saturation magnetization,remanence,and coercivity.Spinel ferrites with a high concentration of rare earth elements have improved direct current resistivity and activation energy.The logarithm of a material's resistance increased from 5.29 to 8.12 Ω·cm as cerium is added.With a change in the amount of cerium,the activation energy goes up from 0.19 to 0.29.By changing the frequency from 5.5 to 9.5 GHz,the dielectric characteristics were determined.As the frequency goes up,the dielectric constant goes down.Spinel ferrites that have been made better in every way can be used in high-frequency applications.