An accurate and fast transient calorimetric ferrite core-loss measurement method is proposed in this article. In contrast to electrical measurements, the accuracy of the calorimetric approach is ...largely independent of the magnetic excitation and operating frequency. However, accurate values of the thermal capacitance and the temperature of the core under test (CUT) are required. Accurate measurement of the specific heat capacity of the core material can be achieved with a differential scanning calorimeter (DSC) or by using the CUT as a dc electric conductor and measuring its thermal response for known Joule heating. Accurate temperature measurements can be realized with NTC temperature sensors. A thorough uncertainty analysis of the presented method is conducted by identifying the impact of each source of uncertainty in the course of a sensitivity analysis. For the considered reference case (R 22.1/13.7/7.9 toroidal core with N49 ferrite material by EPCOS-TDK - 500 kHz/100 mT), the method achieves a total uncertainty with a worst-case value of less than 12% or, in case of a more realistic approach considering a Gaussian distribution of each source of uncertainty, a mean value of −4.3% with a 95% confidence interval of <inline-formula><tex-math notation="LaTeX">\mathbf {\pm }</tex-math></inline-formula>3.2%. The results are verified by means of finite element method (FEM) simulations and experiments. Furthermore, a step-by-step description of the workflow for preparing and conducting the experiments is provided. The proposed method is tested experimentally and compared to a state-of-the-art electrical loss measurement method for MnZn N87 and N49 ferrite cores of EPCOS-TDK. In addition, it is used to measure the loss-map of the NiZn ferrite material 67 from Fair-Rite for very high frequencies up to 50 MHz, which enables the computation of the material's Steinmetz parameters.
•Flower-like FeCoNi/rGO nanosheets are achieved via magnetic-field-assisted (MFA) reduction.•The zigzag-like attachments of neighbored nanosheets constitute the porous flower-like architecture.•The ...optimal sample shows the minimum RL value of -75.95 dB and the broadest fE is 4.69 GHz.•Good dielectric/magnetic heterostructures favor the EM balance for preferable impedance matching.
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Nanostructured magnetic metal/reduced graphene oxide (rGO) composites, benefiting from well-performed losses including high dielectric/magnetic losses, have garnered considerable interest as advanced microwave absorbers (MAs) in recent years. Optional approaches of unique trimetallic/rGO nanostructures, however, are still limited to attain high electromagnetic (EM) absorption and broad bandwidth as well as improved impedance matching. Herein, porous flower-like FeCoNi/rGO nanosheets, synthesized via magnetic-field-assisted (MFA) reduction, presents facilitated microwave absorption performance. The zigzag-like attachments of neighbored nanosheets constitute the porous flower-like architecture; average thickness of the nanosheets is 5–20 nm. The reduction process, determined by appropriate GO dosage, plays a key role to tune geometry and distribution of the flower-like nanosheet structures. The optimal sample, owning a relatively high surface area (157.3 m2 g−1), achieves an impressive reflection loss (RL) intensity of − 75.95 dB and its maximum effective absorption bandwidth (RL ≤ −10 dB) is up to 4.69 GHz, along with improved impedance matching. This work provides a facile and alternative route for exploring other novel nanoalloy-based MAs.
When a superconducting magnetic energy storage (SMES) device exchanges energy with the outside world, the superconducting magnet will be in the environment of dynamic transformation of the current ...and magnetic field, and the AC loss and temperature change caused by this process cannot be ignored, which will seriously affect the long-term stable operation of the magnet. Given the above problems, this paper established an electromagnetic thermal coupling model, taking into account the loss heat source of the magnet and the external environment commutation and other conditions, calculated the loss changes of the magnet under different working conditions, explored the temperature change law, obtained the temperature distribution, and provided a reference for the design of the cooling guide system. The Γ-shaped flux diverters (FDs) were introduced to reduce the loss of the magnet. The results show that the loss is lower when the steady state reference current is maintained at 60% of the critical current. FDs have a more significant suppression effect on the losses generated by dynamic alternating current than the steady-state current.
For HEO@PPy composites, there are mainly eddy current loss and hysteresis loss in the high-entropy oxides. For the effect on the magnetic loss performance, it is weakening for Fe, Ni, and Co ...successively. The composite of HEO(1)-FeNi@PPy has the largest reflection loss with a minimum RL value of −32.04 dB and an effective absorption bandwidth of 5.8 GHz, and the corresponding thicknesses are almost the same, which enables the optimization of both parameters simultaneously. The sample also has the optimal waveband-thickness absorption characteristics. A reciprocal relationship was found between magnetic loss and dielectric loss. By incorporating the HEO(1)-FeNi@PPy powder into paraffin, it was found that the greater the amount of powder material, the higher the electric conduction loss and polarization loss, and the magnetic loss would decrease. The microwave frequency f was found to be the main variable affecting the magnetic permeability and dielectric constant.
•The effect on the magnetic loss of HEOs is weakening for Fe, Ni, Co successively.•There is a reciprocal relationship between magnetic loss and dielectric loss.•Increasing HEO@PPy content can enhance the electric conduction loss and polarization loss, and decrease the magnetic loss.•Microwave frequency f is the main variable affecting the magnetic permeability and dielectric constant.
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•Five high-entropy rare earth hexaborides/tetraboridescomposites were designed and successfully synthesized.•Superior electromagnetic (EM) wave absorbing properties were demonstrated ...for the first time.•Mechanisms for the excellent electromagnetic wave absorbing properties HE REB6/HE REB4 composite were investigated for the first time.•This work opens a new widow to enhance EM wave absorbing properties of the high-entropy rare-earth hexaborides (HE REB6) by promoting dielectric loss without sacrificing magnetic loss.
The increasing electromagnetic hazards including electromagnetic interference and electromagnetic pollution, which were stemmed from massive usage of electromagnetic technology, have triggered widespread concerns. To cope with this challenge, electromagnetic wave absorbing materials with high performance are greatly needed. Composite construction has been widely applied in electromagnetic (EM) wave absorbing materials to achieve high permittivity, high permeability and impedance matching. However, high-temperature stability, oxidation and corrosion resistance are still unignorable issues. Herein, high entropy hexaborides/tetraborides (HE REB6/HE REB4) composites with synergistic dielectric and magnetic losses were designed and successfully synthesized through a one-step boron carbide reduction method. The five as-prepared (Y0.2Nd0.2Sm0.2Eu0.2Er0.2)B6/(Y0.2Nd0.2Sm0.2Eu0.2Er0.2)B4, (Y0.2Nd0.2Sm0.2 Er0.2Yb0.2)B6/(Y0.2Nd0.2Sm0.2Er0.2Yb0.2)B4, (Y0.2Nd0.2Eu0.2Er0.2Yb0.2)B6/(Y0.2Nd0.2Eu0.2Er0.2Yb0.2)B4, (Nd0.2Sm0.2Eu0.2Er0.2Yb0.2)B6/(Nd0.2Sm0.2Eu0.2Er0.2Yb0.2)B4 and (Y0.2 Sm0.2Eu0.2Er0.2Yb0.2)B6/(Y0.2Sm0.2Eu0.2Er0.2Yb0.2)B4 contain two phases of HE REB6 and HE REB4. Among them (Y0.2Nd0.2Sm0.2Eu0.2 Er0.2)B6/(Y0.2Nd0.2Sm0.2Eu0.2Er0.2)B4 (HE REB6/HE REB4-1) and (Y0.2Nd0.2Sm0.2Er0.2Yb0.2)B6/(Y0.2Nd0.2Sm0.2Er0.2Yb0.2)B4 (HE REB6/HE REB4-2) exhibit excellent EM wave absorption properties. The optimal minimum reflection loss (RLmin) and effective absorption bandwidth (EAB) of HE REB6/HE REB4-1 and HE REB6/HE REB4-2 are –53.3 dB (at 1.7 mm), 4.2 GHz (at 1.5 mm) and –43.5 dB (1.3 mm), 4.2 GHz (1.5 mm), respectively. The combination of conducting HE REB4 with magnetism into HE REB6 as a second phase enhances dielectric and magnetic losses, which lead to enhanced EM wave absorption performance. Considering superior high-temperature stability, oxidation and corrosion resistance of HE REB6 and HE REB4, HE REB6/HE REB4 composite ceramics are promising as a new type of high-performance EM wave absorbing materials.
Magnetic/dielectric composites offer good impedance matching for electromagnetic wave absorption, though achieving both strong absorption and broadband absorption in such composites is challenging. ...Herein polypyrrole-Maghemite-graphitic carbon nitride (PPy/γ-Fe2O3/g-C3N4) composites were successfully fabricated via the one-step chemical synthesis of PPy/γ-Fe2O3 nanospheres in the presence g-C3N4 nanosheets. The PPy/γ-Fe2O3/g-C3N4 composites demonstrated outstanding electromagnetic wave (EMW) absorption properties at microwave frequencies. A compositionally optimized PPy/γ-Fe2O3/g-C3N4 composite delivered a minimum reflection loss (RLmin) value of −53.66 dB at 11.92 GHz and the effective absorption bandwidth (EAB, RL < −10 dB) of 5.13 GHz (10.46–15.59 GHz) at a thickness of 2.5 mm. The excellent EMW absorption properties of the composite could be attributed to the introduction of g-C3N4 nanosheets with a lamella structure, which enhanced interfacial polarization losses, multi-reflections, scattering, and impedance matching within the composite. This work offers a simply and effective strategy for the preparation of high-performance EMW absorbers.
•The PPy/γ-Fe2O3/g-C3N4 composites were fabricated via the one-step chemical synthesis method.•In the PPy/γ-Fe2O3/g-C3N4 composites, PPy/γ-Fe2O3 nanospheres decorated on the surface of the g-C3N4 sheets.•The strong reflection loss (−53.66 dB) and bandwidth (5.13 GHz) were achieved.
•FeSi/glass composites are prepared, and glass acts as insulating and adhesive agent in the composites.•Glass particles between FeSi spheres soften and deform to flakes during annealing ...process.•FeSi/glass composites have low power losses.
FeSi/glass composites with different glass content by using low melting glass as adhesive and insulating agent are prepared, and their magnetic properties are investigated. SEM morphology shows that the glass particles between different FeSi spheres deform into flakes after heat treatment, which reveals that glass powder acts as adhesive and insulating agent in the composites. The FeSi/glass composites have high saturation magnetization (up to 210 Am2/kg), low magnetic losses (less than 2100 kW/m3 at 100mT and 100 kHz) and moderate permeability. The moderate eddy current loss obtained by losses separation further indicates that the eddy current between different FeSi spheres is effectively blocked by glass. The advantages of this new preparation process of SMCs are also discussed.
This article presents a SPICE circuit that is able to predict dynamic core losses in ferrite inductors with nonuniform magnetic field. The circuit is supplied by a current generator and provides the ...core power loss as output. The article moves from models available in literature, which has been modified by the introduction of two main improvements allowing to extend the fields of applications. The first one is the design of a circuit that is able to ensure accurate power losses estimation even in the presence of signals affected by noise. The second improvement extends the usability of the model also to those cases where the magnetic material saturates because of high current or temperature effect. Extensive experimental tests to assess the accuracy of the estimations and simulations have been carried out.
Ce3+ doped nickel ferrite was composited with silver (Ag/NiFe2-xCexO4) by the hydrothermal method. Microwave absorption of the synthesized materials was characterized by dielectric and magnetic ...losses, the power absorption coefficient, which reveals the innate behavior of a material, and the reflection coefficient in the form of s11, which reveals the behavior of the material acting as a circuit element, rather than by reflection loss, RL, which is an inappropriate parameter, used in previous calculations by other workers. Experimental values for s11 have been reproduced theoretically. The reasons why some absorption peaks are higher than others have been identified. The results clearly show that there is an interaction between the components of the Ag/NiFe2-xCexO4 composite as it exhibits much better microwave absorption performance than single compound NiFe2O4; compositing with Ag and doping with Ce3+ by appropriate amounts have shifted the microwave resonances to high resistance regions for electric and magnetic dipolar oscillations of NiFe2O4, and dielectric loss is more prominent than magnetic loss for Ag/NiFe2-xCexO4.
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•Alternative procedure other than reflection loss is used in characterization.•A systematical procedure is devised to characterize absorption in experiment.•The procedure is based on previous theoretical investigations.•The results are consistent and reliable.
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