Experimental Electromagnetic Characterization of High Temperature Superconductors Coils Located in Proximity to Electromagnetically Active Materials

The electromagnetic properties of high temperature superconductors(HTS)are characterized with the explicit intent to improve their integration in electric power systems.A tape and a coil made of Bismuth Strontium Calcium Copper Oxide(BSCCO)are considered in the presence of electromagnetically active materials in order to mimic properly the electromagnetic environment typical of electrical machines.The characterization consists of the determining the critical current and the AC losses at different values of the frequency and the transport current.The effects induced by the proximity of the active materials are studied and some related experimental issues are analyzedc.

Graphene-wrapped multiloculated nickel ferrite:A highly efficient electromagnetic attenuation material for microwave absorbing and green shielding

Dedicating to the exploration of efficient electromagnetic(EM)absorption and electromagnetic interference(EMI)shielding materials is the main strategy to solve the EM radiation issues.The development of multifunction EM attenuation materials that are compatible together EM absorption and EMI shielding properties is deserved our exploration and study.Here,the graphenewrapped multiloculated NiFe_(2)O_(4) composites are reported as multifunction EM absorbing and EMI shielding materials.The conductive networks configurated by the overlapping flexible graphene promote the riched polarization genes,as well as electron transmission paths,and thus optimize the dielectric constant of the composites.Meanwhile,the introduction of magnetic NiFe_(2)O_(4) further establishes the magnetic-dielectric synergy effect.The abundant non-homogeneous interfaces not only generate effective interfacial polarization,also the deliberate multiloculated structure of NiFe_(2)O_(4) strengthens multi-scattering and multi-reflection sites to expand the transmission path of EM waves.As it turns out,the best impedance matching is matched at a lower filled concentration to achieve the strongest reflection loss value of−48.1 dB.Simultaneously,green EMI shielding based on a predominantly EM absorption and dissipation is achieved by an enlargement of the filled concentration,which is helpful to reduce the secondary EM wave reflection pollution to the environment.In addition,the electrocatalytic properties are further examined.The graphene-wrapped multiloculated NiFe_(2)O_(4) shows the well electrocatalytic activity as electrocatalysts for hydrogen evolution reaction(HER)and oxygen evolution reaction(OER),which is mainly attributed to the interconnected structures formed by graphene and NiFe_(2)O_(4) connection.The structural advantages of multiloculated NiFe_(2)O_(4) expose more active sites,which plays an important role in optimizing catalytic reactions.This work provides an excellent jumping-off point for the development of multifunction EM absorbing materials,eco-friendliness EMI shielding materials and electrocatalysts.

Ultrahigh Density of Atomic CoFe-Electron Synergy in Noncontinuous Carbon Matrix for Highly Efficient Magnetic Wave Adsorption

Improving the atom utilization of metals and clarifying the M–M’interaction is both greatly significant in assembling high-performance ultra-light electromagnetic wave-absorbing materials.Herein,a high-temperature explosion strategy has been successfully applied to assemble the hierarchical porous carbon sponge with Co–Fe decoration via the pyrolysis of the energetic metal organic framework.The as-constructed hybrid displays a superior reflection loss(RL)value of-57.7 d B and a specific RL value of-192 d B mg-1 mm-1 at 12.08 GHz with a layer thickness of 2.0 mm(loading of 15 wt%).The off-axis electron hologram characterizes the highly distributed numerous polarized nanodomain variable capacitors,demonstrating the dipole and interfacial polarization along the edges of the nanopores.More importantly,the X-ray absorption spectroscopy analysis verifies the mutual interaction between the metal cluster and carbon matrix and the electronic coupling responsible for the greatly improved electromagnetic wave absorption.

Direct Generation of Intense Compression Waves in Molten Metals by Using a High Static Magnetic Field and Their Application

Compression waves propagating through molten metals are contributed to degassing, accelerating reaction rate,removing exclusions from molten metals and refining solidification structures during metallurgical processing of materials. In the present study, two electromagnetic methods are proposed to generate intense compression wavesdirectly in liquid metals. One is the simultaneous imposition of a high frequency electrical current field and a staticmagnetic field; the other is that of a high frequency magnetic field and a static magnetic field. A mathematical modelbased on compressible fluid dynamics and electromagnetic fields theory has been developed to derive pressure distributions of the generated waves in a metal. It shows that the intensity of compression waves is proportional to thatof the high frequency electromagnetic force. And the frequency is the same as that of the imposed electromagneticforce. On the basis of theoretical analyses, pressure change in liquid gallium was examined by a pressure transducerunder various conditions. The observed results approximately agreed with the predictions derived from the theoreticalanalyses and calculations. Moreover, the effect of the generated waves on improvement of solidification structureswas also examined. It shows that the generated compression waves can refine solidification structures when they wereapplied to solidification process of Sn-Pb alloy. This study indicates a new method to generate compression wavesby imposing high frequency electromagnetic force locally on molten metals and this kind of compression waves canprobably overcome the difficulties when waves are excited by mechanical vibration in high temperature environments.

Co-Ni Electromagnetic Coupling in Hollow Mo_(2)C/NC Sphere for Enhancing Electromagnetic Wave Absorbing Performance

For enhancing the electromagnetic wave(EW)attenuation and adsorption,rational constructing and homogeneously distributing bimetallic electromagnetic coupling units in hollow structure is an effective way,but hard to achieve.Herein,a CoNi-doped hybrid zeolite imidazole framework was synthesized as precursor,which was further converted into a hollow CoNi-bimetallic doped molyb-denum carbide sphere(H-CoNi@MoC/NC)through a two-step etching and calcination strategy.At the loading amount of 15 wt%,a strong absorption of minimum reflection loss(RL_(min))of-60.05 dB at 7.2 GHz with the thickness of 3.1 mm and a wide effective ad-sorption bandwidth(EAB)of 3.52 GHz at the thickness of 2.5 mm were achieved,which was far beyond the reported MoC-based metallic hybrids.The crucial synergistic Co-Ni electromagnetic coupling effect in the composite was characterized,not only enhanc-ing the dipolar/interfacial polarization,but also promoting the impedance matching,displaying the optimized EW absorbing perfor-mance.

Electromagnetic Processing of Materials

Pulsed external field, including electric, magnetic, ultrasonic and laser, as aninstantaneous high energy input method with high efficiency and low energyconsumption, have long been known to can modify the microstructure and propertiesof materials. This includes electroplasticity, magnetoplasticity, phase transformations,recrystallization, grain refinement, texture control, inclusion removal.

Bifunctional Two-Dimensional Nanocomposite with Electromagnetic Wave Absorption and Anti-bacterial Performance

In current electronic information era,the complex application circumstance of 5G devices pursues the exploration of multi-functional electromagnetic wave(EMW)absorbent materials and it has become the crucial focus in industrial development.A two-dimensional(2D)graphite nanosheet decorated by nickel nanocapsules(2D graphite/Ni@C nanocomposite)was fabricated to possess the EMW absorption and the Escherichia coli(E.coli)anti-bacterial performance simultaneously.By adjusting the filling ratio and injecting nitrogen doping,the value of minimum reflection loss is−36.08 dB and the effective absorption bandwidth reaches to 5.12 GHz(from 11.4 to 16.52 GHz)with the mass ratio of 30 wt%and the absorber thickness of 2 mm.This 2D nanocomposite simultaneously gets an excellent anti-bacterial function expressing an E.coli anti-bacterial rate of 92%during 24 h which is significantly correlated to the interaction between the nanostructure of the 2D nanographite and the nickel ion released from Ni@C nanocapsules.This work provides a new approach to develop a promising 2D anti-bacterial EMW absorber.

Spontaneous emission in non-local materials

Light–matter interactions can be strongly modified by the surrounding environment.Here,we report on the first experimental observation of molecular spontaneous emission inside a highly non-local metamaterial based on a plasmonic nanorod assembly.We show that the emission process is dominated not only by the topology of its local effective medium dispersion,but also by the non-local response of the composite,so that metamaterials with different geometric parameters but the same local effective medium properties exhibit different Purcell factors.A record-high enhancement of a decay rate is observed,in agreement with the developed quantitative description of the Purcell effect in a non-local medium.An engineered material non-locality introduces an additional degree of freedom into quantum electrodynamics,enabling new applications in quantum information processing,photochemistry,imaging and sensing with macroscopic composites.