Fabricating microwave absorbers (MA) with strong attenuation capability and lightweight is still a challenge problem, which limit their further applications in our daily life. Herein, magnetic vortex ...core-shell Fe3O4@C nanorings (FNR-C) with excellent microwave absorption property have been successfully prepared by a facile strategy. Electron holography analysis is carried out to detect the magnetic vortex structure of FNR-C. Furthermore, the microwave absorption properties of these samples are investigated in terms of complex permittivity and permeability. The FNR-C exhibits a strong reflection loss value of −61.54 dB at 16.9 GHz with a thickness of 1.50 mm and a low filling ratio of 25%. It’s the first time to take magnetic vortex into discussion. The unexceptionable attenuation ability is mainly attributed to the eddy current loss enhanced by combination of confinement vortex and strain-driven vortex. Besides, thanks to the dielectric feature of carbon, the Fe3O4 core is beneficial for the impedance match. Our findings provide a guidance to the development of nanoferrite@carbon hybrid materials with excellent microwave absorption property from the perspective of magnetic vortex.
Nanoferrite@carbon hybrid materials exhibited an excellence electromagnetic absorption performance due to the synergistic effects of the magnetic and dielectric loss among Fe3O4 nanorings and carbon layer. Display omitted
This paper discloses two high-sensitivity probes for Eddy Current Nondestructive Test (NDT) of buried and surface defects. These probes incorporate eight and 32 magnetoresistive sensors, ...respectively, which are optimized for high sensitivity and spatial resolution. The signal processing and interfacing are carried out by a full-custom application-specific integrated circuit (ASIC). The ASIC signal chain performs with a thermal input-referred noise of 30 nV/<inline-formula><tex-math notation="LaTeX">\sqrt{\text{Hz}}</tex-math></inline-formula> at 1 kHz, with 66 mW of power consumption, in a die with 3.7×3.4 mm<inline-formula><tex-math notation="LaTeX">^2</tex-math></inline-formula>. NDT results are presented, showing that there is an increase in spatial resolution of surface defects when contrasted to prior art, enabling the probes to resolve defects with diameters of 0.44 mm, pitches of 0.6 mm, and minimum edge distance as low as 0.16 mm. The results also show that the probe for buried defects is a good all-round tool for detection of defects under cladding and multiple-plate flat junctions.
Confirming the origin of Gilbert damping by experiment has remained a challenge for many decades, even for simple ferromagnetic metals. Here, we experimentally identify Gilbert damping that increases ...with decreasing electronic scattering in epitaxial thin films of pure Fe. This observation of conductivitylike damping, which cannot be accounted for by classical eddy-current loss, is in excellent quantitative agreement with theoretical predictions of Gilbert damping due to intraband scattering. Our results resolve the long-standing question about a fundamental damping mechanism and offer hints for engineering low-loss magnetic metals for cryogenic spintronics and quantum devices.
•Co2Z hexaferrites and Fe powders are mixed and compacted into to form toroidal Co2Z/Fe SMCs.•Co2Z hexaferrites increase the resistance of Co2Z/Fe SMCs and reduce eddy-current loss.•Co2Z hexaferrites ...improve the density of Co2Z/Fe SMCs and reduce the hysteresis loss.•Co2Z/Fe SMCs possess the higher permeability and lower core loss at high-frequency than Fe SMCs.•Air gaps between Fe particles are filled with Co2Z hexaferrites.
Single-phase Co2Z hexaferrite with excellent middle to higher frequency performance was synthesized via the sol–gel method, and then were mechanically mixed with Fe powders and compacted to form toroidal Co2Z hexaferrites/Fe soft magnetic composites (Co2Z/Fe SMCs). After characterization with XRD, SEM, EDS, VSM and B-H Analyzer, the influence of Co2Z hexaferrites on the microstructures, AC and DC magnetic performance were investigated in detail. Air gaps between Fe powders are filled with Co2Z hexaferrites at the optimized content and the density of Co2Z/Fe SMCs increases. Co2Z hexaferrites effectively improve the soft magnetic performance of Co2Z/Fe SMCs at middle to higher frequency. The permeability and DC bias performance of Co2Z/Fe SMCs increased with the Co2Z hexaferrites content up to the maximum for 1 wt% Co2Z/Fe SMCs, and then decreased. While the changing trend of the core loss is opposite to the permeability and reaches the minimum for 1 wt% Co2Z/Fe SMCs. Co2Z hexaferrites not only increase the resistance of Co2Z/Fe SMCs and reduce the eddy-current loss, but also improve the interface microstructures and optimize the magnetic circuit of Co2Z/Fe SMCs.
Applying life estimation approaches to determine in-service life of structures and plan the inspection schedules accordingly are becoming acceptable safety design procedures in aerospace. However, ...these design systems shall be fed with reliable parameters related to material properties, loading conditions and defect characteristics. In this context, the role of non-destructive (NDT) testing reliability is of high importance in detecting and sizing defects. Eddy current test (ECT) is an electromagnetic NDT method frequently used to inspect tiny surface fatigue cracks in sensitive industries. Owing to the new advances in robotic technologies, there is a trend to integrate the ECT into automated systems to perform NDT inspections more efficiently. In fact, ECT can be effectively automated as to increase the coverage, repeatability and scanning speed. The reliability of ECT scanning, however, should be thoroughly investigated and compared to conventional modes of applications to obtain a better understanding of the advantages and shortcomings related to this technique. In this contribution, a series of manual and automated ECT tests are carried out on a set of samples using a split-D reflection differential surface probe. The study investigates the level of noise recorded in each technique and discuss its dependency on different parameters, such as surface roughness and frequency. Afterwards, a description of the effect of crack orientation on ECT signal amplitude is provided through experimental tests and finite element simulations. Finally, the reliability of each ECT technique is investigated by means of probability of detection (POD) curves. POD parameters are then extracted and compared to examine the effect of scanning index, frequency and automation on detection reliability.
Capacitive power transfer (CPT) technology is an effective and important alternative to the conventional inductive power transfer (IPT). It utilizes high-frequency electric fields to transfer ...electric power, which has three distinguishing advantages: negligible eddy-current loss, relatively low cost and weight, and excellent misalignment performance. In recent years, the power level and efficiency of CPT systems has been significantly improved and has reached the power level suitable for electric vehicle charging applications. This paper reviews the latest developments in CPT technology, focusing on two key technologies: the compensation circuit topology and the capacitive coupler structure. The comparison with the IPT system and some critical issues in practical applications are also discussed. Based on these analyses, the future research direction can be developed and the applications of the CPT technology can be promoted.
Eddy current array testing (ECAT) is a useful tool in evaluating defect sizes. However, it is difficult for ECAT to evaluate the inner defects in ferromagnetic materials due to thin skin effect. In ...this article, direct current (dc) magnetization-based ECAT (DCMECAT) is proposed to quantify buried defects existing in the inner surface of steel plates. Relying on permeability disturbance in the defect vicinity, DCMECAT can build links between the testing signals and defect sizes. The results show that the performance of evaluating defect sizes is better under the saturated magnetization state. Further, three features, i.e., the signal width, the peak voltage, and the contour orientation, are proposed to evaluate the width, the depth, and the orientation of defects, respectively. Relationships between features and defect sizes are investigated by using least-squares regression. Further, a testing example is shown in this article, and the evaluation error is 14%.
•A method based on signal slicing and recombination is proposed to generate PECT image sequences.•The evaluation of sequence images is carried out through image quality assessment and quantitative ...identification.•The feasibility of the image sequence is verified for the two different subtracted signals (ASS and NDSS).•The influence of defects was explained by visualizing the diffusion of eddy currents using a finite element model.
Pulsed eddy current testing (PECT) has the advantages of rich information, efficiency and noncontact among defect nondestructive testing. Pulsed eddy current imaging technology also has a wide range of applications. However, the imaging method based on single feature is mostly adopted at this stage. In order to make better use of pulsed eddy current signals, signal slice based method was proposed for pulsed eddy current sequence imaging. Through the difference analysis of air-subtracted signal (ASS) and non-defect-subtracted signal (NDSS), sequence imaging in different ways is carried out. The influence of defects was explained by visualizing the diffusion of eddy currents in different specimens using a finite element model. ASS and NDSS image sequences were evaluated through image quality evaluation and quantitative identification. The result shows that there are some image frames in the image sequence that are better than the images generated by a single feature value in the image quality evaluation and quantitative analysis. It proves that the image sequence contains more defect information, which also illustrates the information richness of pulse eddy current detection.
In this paper, a superhigh-speed permanent-magnet generator (SHSPMG) which has an alloy sleeve on the rotor outer surface is investigated. The purpose of the sleeve is to fix the permanent magnets ...and protect them from being destroyed by the large centrifugal force. However, the sleeve material characteristics have much influence on the superhigh-speed machine, and therewith, most of rotor eddy-current losses are generated in the alloy rotor sleeve, which could increase the device temperature. Taking a 117-kW 60 000-r/min SHSPMG as an example, the influence of the sleeve on the generator output performance is analyzed when the generator sleeve is made of stainless steel, carbon fiber, copper-iron alloy, and copper. In addition, the eddy-current loss distributions could be gotten, and therewith, the variations of the eddy-current losses in different kinds of sleeves are analyzed. Based on the 3-D coupling field between the fluid and temperature, the temperature distributions were obtained when the sleeve adopts different materials. Moreover, the temperature variations of the permanent magnets are further analyzed. The obtained conclusions may provide some references for the design and analyses of the SHSPMG.
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