Ferrite Absorber Research Articles

Tunable and wideband high-performance rare earth-doped Ni-Mg-Cu-Zn nano ferrite-based meta-absorbers for C-band application

Due to advanced technology, electromagnet interference and dissipation problems in the electronic and portable devices at GHz range are increasing daily. Magnetic absorbing materials with outstanding electromagnetic properties, wide bandwidth, and strong absorption are highly desirable. The present investigation deals with the preparation of Ni-Mg-Cu-Zn (NMCZ) substituted nano ferrites with composition of Ni0.3Mg0.2Cu0.3Zn0.2X0.02Fe1.98O4 (X = Nd, Ho, Pr, Gd, Yb). X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), a vibratory sample magnetometer (VSM), and a Vector network analyzer (VNA) were used to investigate these rare earth-doped nanocrystalline ferrites' features. XRD reveals the single spinel phase structure in all Ni-Mg-Cu-Zn ferrites. FTIR spectroscopy shows the presence of tetrahedral and octahedral bands of spinel ferrites. FESEM images reveal the lowest agglomeration for the Ho-doped NMCZ nano-spinel ferrites sample. TEM images show the hexagon shapes of the Yb- and Nd-doped NMCZ ferrites. Pr-doped NMCZ ferrites show more coercivity than other rare earth metals substituted NMCZ nanocrystalline ferrites. VSM analysis was used to calculate the magnetic features like initial permeability, magnetic anisotropy constant, remanence, coercivity, and magnetic moment. High-frequency switching field distributions (SFD) analyses were also investigated. Magnetodielectric characteristics such as losses, permittivity, modulus, Q, ac conductivity, and impedance of the Nd-, Ho-, Pr-, Gd-, Yb-doped Ni-Mg-Cu-Zn ferrites were evaluated. The minimum reflection loss (–57.3 dB) is found at 1.4 GHz for Pr-doped Ni-Mg-Cu-Zn ferrite absorber. However, the reflection loss (RL) of –53.9 dB at 2.9 GHz is observed for Ho-doped Ni-Mg-Cu-Zn ferrite absorber. Soft magnetization, low coercivity, outstanding magnetodielectric, and absorption properties of the Nd-, Ho-, Pr-, Gd- and Yb-doped Ni-Mg-Cu-Zn ferrites are suitable candidates for absorption in telecommunication, defense, and technological industries.

Electrical properties of ferrite absorber in the frequency range from 15 GHz to 45 GHz

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Compact design of the 166.6 MHz superconducting cavity and its beamline elements for HEPS

The High Energy Photon Source (HEPS) is a 6 GeV diffraction-limited synchrotron light source under construction in Beijing. It will use five 166.6 MHz superconducting radio frequency (rf) cavities to accelerate the 200 mA electron beam in the storage ring. In the current lattice design, each straight section is 6 meters long to accommodate two 166.6 MHz cavities. The cavity adopts β=1 quarter-wave geometry, and the damping of the higher order modes is realized by using an enlarged cavity beam pipe to 505 mm and a ferrite absorber installed on the beam pipe. The low rf frequency, as well as the large beam aperture, added great challenges to the design of the 166.6 MHz cavity module to fit into a strictly limited longitudinal space. In addition, heat load optimization for the transition from room temperature to the cryogenic temperature, smooth tapering from the 505 mm beam aperture to the small diameter of the gate valves for impedance control, proper collimation of the synchrotron light to prevent thermal damage of delicate components, are also demanding requirements for a compact design. Accessibilities are also preserved for tuners and vacuum components to enable online maintenance. Finally, rf field leakage in the vacuum seal groove of the cavity is carefully examined to prevent overheating on the superconducting flange, which, in the worst scenario, may cause a thermal runaway, thus limiting the achievable accelerating gradient of the cavity. This paper presents the first compact design of the 166.6 MHz srf section for HEPS.

Co-substituted Ca–La magnetoplumbite ferrite microwave absorbers at 100 GHz

Millimeter wave absorption exceeding 70 GHz has been performed in a Co-substituted Ca–La magnetoplumbite (M-type) ferrite. A polymerized complex method was used to increase the substitution of La and Co ions in the M-type ferrite. The increase in the magnetic anisotropy field combined with the remaining significant saturation magnetization results in good magnetic resonance absorption in the millimeter range of 70–100 GHz. Above 70 GHz, good millimeter wave absorption of more than −20 dB was achieved in 0.25 mm thickness plates of Ca0.46La0.54Fe11Co0.28O19-η and Ca0.42La0.58Fe11Co0.58O19-η. Highly Co-substituted Ca–La M-type ferrites may, thus, be promising candidates for magnetic absorption materials operating in frequencies of up to 100 GHz.

Review of ferrite-based microwave-absorbing materials: Origin, synthesis, morphological effects, dielectric/magnetic properties, composites, absorption mechanisms, and optimization

With the advancement and up-gradation of wireless technology, people worldwide are surrounded by microwaves, however, with the brighter side comes the darker side too. These microwave/electromagnetic wireless signals interfere with the environment/mankind and are referred to as electromagnetic interference (EMI)/electromagnetic or microwave pollution. Microwave/electromagnetic absorbers are used to mitigate this EMI or electromagnetic pollution. Researchers have been working on microwave absorbents of different kinds to save humans, their gadgets, electronically printed cards, etc. to create a healthy and radiation-free environment. Recently, there is an advancement in different forms of ferrite absorbers. This review presents a description of what are ferrite-based microwave absorbers, the preparation method of absorbers, the working principle, and detailed insights involving necessary models and mechanisms regarding microwave absorption. It also encapsulates the description of how the ferrite composition, morphology, doping, reflection loss peaks, and matrix account for optimizing the performance of the absorbers. The history, origin, and ancestral use of microwave absorbers are mentioned, and how technological needs lead to advancement in ferrite microwave absorbers has also been discussed. A picture is portrayed of what are microwaves, their potential hazards, and how these hazards should be taken care of with the help of ferrite microwave absorbers.

Highly efficient absorber with enhanced magnetoelectric properties based on Y, Gd, and Pr doped NMZ nanoferrites

NMZ ferrites doped with rare earth having spinel composition Ni0.5Mn0.3Zn0.2X0.02Fe1.98O4, whereas X = Y, Pr and Gd were synthesized by sol gel auto-ignition method. XRD, FESEM, VSM and VNA were used to determine the phase, microstructural, magnetic and electromagnetic properties of rare earths doped NMZ ferrite. XRD analysis confirms the single phase of the rare earths doped NMZ ferrite. FESEM images shows Pr doped NMZ ferrite has less agglomerations and more porous structure as compared to NMZ and other rare earths doped NMZ ferrites. Magnetic analysis shows the enhancement in saturation magnetization and remanence with the doping of Y, Pr and Gd in NMZ ferrite. Dielectric properties were determined. Gd doped NMZ ferrite depicted higher ac conductivity, dielectric constant and other electromagnetic and related dielectric properties as compared to Pr-NMZ, Y-NMZ and NMZ ferrite. Similarly, Gd- NMZ spinel ferrite depicted maximum M'' to other doping contents (Y, Pr) and pure NMZ ferrite. The high saturation Q-factor of Pure NMZ spinel ferrite NPs, Y- NMZ, Pr-NMZ and Gd-NMZ were observed at 1.57 GHz, 1.58 GHz, 3.65 and 4.01 GHz frequency regions, respectively. NMZ and RE doped NMZ ferrite absorbers with thin substrate as absorber were simulated using FDTD method. The maximum value of absorptivity for Gd-NMZ at 2.4 GHz were noticed from the simulated absorbers. The absorptivity was also increased with the different incident angles. Therefore, Gd doped NMZ are more preferable for absorption devices in high frequency region.

Design and performance tests of a modular 166.6-MHz 50-kW compact solid-state power amplifier for the HEPS-TF project

A 166.6-MHz 50-kW power transmitter is required to drive the dressed superconducting radio-frequency (RF) cavity during horizontal tests and to condition the fundamental power couplers as well as higher-order-mode ferrite absorbers. A highly modular yet compact amplifier adopting solid-state technologies was therefore developed in the framework of High Energy Photon Source - Test Facility. All power amplifier and power supply modules are pluggable from the front panel of the amplifier system. A 3-stage power combining topology was realized by using 32 power amplifier modules, 4 eight-way stripline power combiners, 2 two-way 35-kW coaxial power combiners, and 1 two-way 65-kW coaxial power combiner. Each power amplifier module is equipped with individual circulator and load utilizing an optimized cooling circuit design to ensure the entire amplifier system to be operational in both full-transmission and full-reflection scenarios. No final-stage high-power circulator or load is needed. The amplifier system is tunable in pulsed mode for any duty factors and fully functional in the continuous-wave mode as required. Excellent noise suppression and high wall-plug-to-RF efficiency were achieved at nominal power. Comfortable redundancies for both power amplifier and power supply modules were reserved to compensate for any hardware degradations during operations. Temperature, current, voltage, and RF signal of each module as well as cooling were monitored and managed by using EPICS in the control system of the amplifier. An interlock system was also integrated as well as an event logging system for post-mortem analysis. The system has accumulated over 2000 hours of operation. The design and performance tests of the first 166.6-MHz 50-kW modular solid-state power amplifier are presented.

Design and Optimization of the High Order Modes Damper for a 1.5 GHz Superconducting Harmonic Cavity

The installation of a superconducting radio-frequency (SRF) cavity can improve the beam lifetime via increasing the electron bunch length. A prototype 1.5-GHz SRF passive harmonic cavity working at 4.5 K was designed for The Taiwan Photon Source (TPS). As the beam might become unstable because of the coupled-bunch instability resulting from Higher Order Modes (HOMs) of the SRF harmonic cavity, HOMs damping of this cavity is an important issue. Ferrite absorbers placed in the beam tubes are designed to damp the HOMs. A theoretical calculation for the instability threshold for the HOMs is given. A tracking method is used to simulate the instabilities for operation with this HOMs-damped SRF harmonic cavity. The design and optimization of the HOMs damper, as well as the results of instability studies for this SRF harmonics cavity, are presented here.

Ultrathin 3-D Frequency Selective Rasorber With Wide Absorption Bands

A novel ultrathin 3-D frequency-selective rasorber (FSR) with wide lower and upper absorption bands is presented. The wide absorption band is achieved by using a commercial ferrite absorber and the ultrathin profile is realized using a slow wave structure. The ferrite absorber is very thin and operates over a wide frequency band due to its strong magnetic loss. The attractive low insertion loss feature is obtained through bypassing the ferrite absorber with a series $L$ – $C$ circuit at the passband frequency. An equivalent circuit model is proposed to analyze the physical mechanism of the proposed 3-D FSR and to formulate the design equations. A prototype of the proposed 3-D FSR is fabricated and measured. Tested results show a bandwidth (BW) of 26.6% for the transmission band with insertion loss less than 3 dB and a fractional bandwidth of 163.6% for reflection coefficient less than −10 dB can be obtained. A key feature of the proposed FSR is that its thickness is only $0.086\lambda _{c}$ , where $\lambda _{c}$ is the free-space wavelength at the center frequency of the passband. Moreover, simulated results show that the proposed structure exhibits stable frequency responses under oblique incidence up to 45°.

Dual-template hydrothermal synthesis of multi-channel porous NiCo2O4 hollow spheres as high-performance electromagnetic wave absorber

Dual-template hydrothermal method was adopted for the synthesis of NiCo2O4 materials. The D-glucose acted as the hard template and the three kinds of soft templates, i.e., nonionic polyvinylpyrrolidone (PVP), anionic sodium dodecyl benzene sulfonate (SDBS) and cationic hexadecyl trimethyl ammonium bromide (CTAB) were selected to synthesize NiCo2O4 materials. We found that the species of the soft templates play significant role in the determination of products’ morphologies. Flower-like, flower-like spherical and multi-channel porous hollow spheres structured NiCo2O4 could be obtained by utilization of PVP, CTAB and SDBS, respectively. When employed as the electromagnetic (EM) wave absorbers, the multi-channel porous NiCo2O4 hollow spheres possessed the best EM wave absorption performance. The reflection loss (RL) value lower than −10 dB was up to 5.44 GHz and could be achieved at thin thickness of 1.8 mm. The minimum RL value corresponding to this thickness reached to −31.1 dB as well. The outstanding EM wave absorption performance was ascribed to the unique multi-channel porous hollow spheres structure, which could provide abundant interfaces between absorbers-air thus promoting the interfacial polarization. Additionally, the multiple reflections and scattering, dipole polarization and eddy current loss conjointly accounted for the superior attenuation behavior. The facile synthetic route and the high EM wave absorption performance of multi-channel porous NiCo2O4 hollow spheres may offer a novel strategy for the preparation of high-performance ferrite EM wave absorbers.

On the design and fabrication of a large GTEM cell and its challenges

This paper presents the design of a large Gigahertz Transverse Electromagnetic (GTEM) cell for Electrical/Electronic Sub-Assembly (ESA) testing of a car or other information technology (IT) equipment as well as the challenges of its design and fabrication. The 7.5 meter long and 4 meter width and 4 meter height dimensions of this cell are large enough to test ESAs inside. The operating frequency band is from 30 MHz to 6 GHz based on CISPR standards. To increase the operating frequency of the GTEM and to improve the uniformity of the wave, hybrid absorbers are mounted at the end wall. These absorbers consist of ferrite tile and pyramid absorbers, which have large bandwidth and high performance. The dimensions of the GTEM cell are too large and therefore full wave simulation is difficult and time consuming. In this paper, we have introduced a two-step method to convert a pyramidal absorber into a one-layer flat absorber. This technique simplifies our GTEM cell full wave simulation. On the fabrication side, the effect of distortion of a long metal sheet on the performance of the room are numerically examined. Finally, the acceptable measurement results of the GTEM are reported.

Enhanced microwave absorption properties of barium ferrites by Zr4+-Ni2+ doping and oxygen-deficient sintering

To achieve excellent microwave absorption properties within the frequency range of 2–18 GHz, Zr4+-Ni2+ co-doped barium ferrites BaFe12-2x(ZrNi)xO19 have been synthesized through a sol–gel process and subsequent sintering. Broadened bandwidth of ∼6.9 GHz and strong microwave absorption of −59.3 dB is attained for the ferrite with x = 0.6 and sintering in Ar. The excellent microwave absorption properties are attributed to both the effective shifting of resonance peaks by Zr4+-Ni2+ substitution and the enhanced dielectric loss by generating lattice vacancies through the oxygen-deficient sintering process. This work would be helpful to understand the nature of manipulating the resonance behaviors and further improving the microwave absorption efficiency of traditional ferrite absorbers.

Broadband polarization-insensitive microwave-absorbing composite material based on carbon nanotube film metamaterial and ferrite

To meet the requirements of efficient broadband microwave-absorbing materials for a variety of technological equipment, a composite material based on a carbon nanotube (CNT) film metamaterial and ferrite is designed and fabricated in this study. To this end, available methods for the design and fabrication of the CNT film metamaterial are examined, and the optimal design of the CNT film metamaterial and a ferrite absorber is proposed. The broadband microwave-absorbing composite material was prepared by combining the CNT film with the ferrite absorber according to the design, and the microwave-absorbing properties of the composite material were studied. The results of experiments show that the reflectivity of the composite material was lower than −8 dB at 4–18 GHz at a bandwidth of 14 GHz, which is significantly better than the reflectivity obtained using a single ferrite absorber. Moreover, the composite material is insensitive to electromagnetic wave polarization.

Design of a multilayer composite absorber working in the P-band by NiZn ferrite and cross-shaped metamaterial

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.

Neutron Diffraction Analysis and Electromagnetic Properties of Ultrasonic Wet-Magnetic Separated NixZn1−xFe2O4 Nano-powders

Nano-sized ferrite powders less than 50 nm were prepared through combustion reaction followed by pulverizing and separating through ultrasonic-wet magnetic classification processes to study the electromagnetic properties of the nano-sized ferrites for developing an high performance electromagnetic interference filter. Neutron diffraction analysis of the ferrites prepared at 10 MPa of oxygen pressure shows that the final phase is Ni0.33Zn0.67Fe2O4 (χ2 = 1.48), which lattice parameter is 0.8412(2) nm. The residual magnetization, maximum magnetization, coercive force, susceptibility and Curie temperature of Ni0.33Zn0.67Fe2O4 particles are 0.88 Wb/m2 kg, 7.749 Wb/m2 kg, 1292 A/m, 0.068 m3/kg, and 413.93 K, respectively. Finally, the nano-sized ferrite particle less than 50 nm with more than 99% purity were obtained. The increasing frequency reduced complex permeability which real value (μr0) shows the maximum value at the less than 0.5 GHz. The dielectric constants of the powders are er′ = 5.7 and er″ = 2.5. The nano-sized Ni0.33Zn0.67Fe2O4 ferrite absorber works effectively in the range of 3–5 GHz. Typical FESEM image of Ni0.33Zn0.67Fe2O4 nano-powders.

Efficient ferrite/Co/porous carbon microwave absorbing material based on ferrite@metal–organic framework

A series of ferrite/Co/porous carbon materials were prepared by the situ-thermal carbonization of ferrite/ZIF-67 under N2 atmosphere, and the microwave absorption properties have also been investigated. The magnetoelectric synergistic microwave absorbing material is promising as an efficient microwave absorbing material. The component absorbers with unique porous carbon structure make great contribution to the impedance match, interface polarization, magnetoelectric synergistic effect, and multiple reflection and scattering loss. The carbonization temperature indicates a crucial effect on the porous structure, and too high temperature will result in the collapse of the porous structure. The ferrite/Co/porous carbon fabricated at 500°C (FC500) exhibits the most enhanced microwave absorbing performance. The maximum reflection loss (RL) of FC500 reaches −31.05dB at 14.32GHz, and the effective absorption bandwidth (RL≤−10dB) is 4.8GHz (12.24GHz–17.04GHz) corresponding to a thickness of 1.5mm. The maximum reflection loss (RL) can reach −47.31dB at 8.4GHz, and absorption bandwidth (RL≤−10dB) is 2.72GHz (6.80GHz–9.52GHz) with a thickness of 2.5mm. Thus, the component absorption materials can significantly decrease the weight of ferrite absorbers, ascribing to the thinner optimum thickness.

The effect of the base composition and microstructure of nickel-zinc ferrites on the level of absorption of electromagnetic radiation

Promising absorbing materials include Ni—Zn ferrites, as they quite intensively absorb electromagnetic waves in the frequency range from 50 to 1000 MHz. The electromagnetic properties of Ni—Zn ferrite absorbing materials obtained by different technological methods were studied in this paper. A model making it possible to evaluate the dielectric permeability of the ferrite material, depending on the microstructure parameters and electrophysical properties of grain boundaries, was proposed. The influence of base composition and microstructure on the amount of absorption of electromagnetic radiation by Ni—Zn ferrite absorbing materials was determined. It was stated that the increase of the content of excess Fe2O3 to 51.0 mol % leads to the shift of the frequency range of the absorption of electromagnetic radiation towards lower frequencies. It can be explained by the increase of the dielectric and magnetic permeability of ferrite. Moreover, the introduction of an excess of Fe2O3 in the grinding stage of the synthesized burden is more efficient. It was revealed that increasing the sintering temperature to 1350°C also shifts the frequency range of absorption of electromagnetic radiation towards lower frequencies. Probably it is caused by the increase of the dielectric and magnetic permeability of ferrite and the shift of the resonance frequency of domain walls as a result of the formation of a coarse-grained structure.

The research of EM wave absorbing properties of ferrite/silicon carbide/graphite three-layer composite coating knitted fabrics

The polyester knitted fabric was used as a basilicon carbide structure material. A three-layer composite coating finishing was applied to the structure material using ferrite, silicon carbide, and graphite absorbing materials. The single factor test method was used in this series of research. The impact on dielectric constant and loss tangent of absorbtion of each agent and the coating thickness of each layer were studied. From these results, the three-layer composite coating materials that had excellent absorbing properties were selected and prepared. The results showed that when the ferrite (60 wt%) was used as a bottom layer, the silicon carbide (36 wt%) was used as a middle layer and the graphite (24 wt%) was used as a surface layer with the respective thickness of 0.5, 0.3, and 0.3 mm, an excellent microwave absorbing property was noted for the three-layer composite coating material. In order to meet the requirements for the engineering field, physilicon carbideal and mechanical properties of the microwave absorbing materials were also characterized.

Design of grid-type microwave absorbers with high-permittivity composites of Ag-coated Ni-Zn ferrite particles

We investigate the microwave absorbing characteristics in grid-shaped rubber composite sheets containing Ag-coated Ni-Zn ferrite particles. The improvements in the microwave absorbance are obtained through the insertion of a periodic air cavity in the high-permittivity composites. In the bulk specimens containing conductive and magnetic Ag-coated ferrite microspheres, the impedance matching is not satisfied due to the high dielectric permittivity of the composite. The insertion of an air cavity in those absorbers reduces the permittivity and permeability, and thereby leading to impedance matching at a higher frequency. In the grid-type absorber with an optimum air cavity volume rate, the reflection loss can be decreased to as low as −30 dB at 10.5 GHz with a small layer thickness of 2 mm. The proposed grid-type microwave absorber has advantages of a small matching thickness and a considerable reduction in weight in comparison with conventional ferrite composite absorbers.

EFFECT OF THE BASE COMPOSITION AND MICROSTRUCTURE ON THE LEVEL OF ABSORPTION OF ELECTROMAGNETIC RADIATION IN NICKEL−ZINC FERRITE

Promising absorbing materials include Ni—Zn−ferrites, as they quite intensively absorb electromagnetic waves in the 50 MHz to 1000 MHz frequency range. In this paper we have studied the electromagnetic properties of Ni—Zn ferrite absorbing materials obtained in different technological modes. We propose a model that allows one to evaluate the dielectric constant of the ferrite material depending on the parameters of the microstructure and electrical properties of grain boundaries. Influence of base composition and microstructure on the level of absorption of electromagnetic radiation by Ni—Zn ferrite absorbing materials has been found. An increase in Fe₂O₃ excess to 51 % has been found to shift the frequency interval of electromagnetic radiation absorption towards lower frequencies, and this effect can be explained by an increase in the dielectric and magnetic constants of ferrite. Introduction of excess Fe₂O₃ in step 2 of grinding proved to be more efficient. An increase in the sintering temperature to 1350 °C also provides for a shift of electromagnetic radiation absorption frequency interval towards lower frequencies, which can be explained by an increase of the dielectric and magnetic constants of ferrite and resonance frequency shift of domain walls due to the formation of a coarse−grained structure.