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Partial discharge (PD) is one of the key factors leading to premature insulation failure of film capacitors used in pulse power devices. To study the effect of frequency on the PD characteristics of biaxially oriented polypropylene (BOPP) film, a sphere-plate electrode was used to simulate defects of the air gap between the film layers. PD experiments of the BOPP film were carried out under 1, 10, 100, 500 Hz, and 1 kHz with a rising edge of 65 ns and a pulse width of 300 ns. The results show that the repetitive partial discharge inception voltage (RPDIV), the number of discharges, the rising stage discharge (RSD) amplitude, and the falling stage discharge (FSD) time-lag, all show an increase and then decrease with increasing pulse frequencies and reach a maximum value at a pulse frequency of 100 Hz. Moreover, the FSD discharge amplitude and the RSD discharge time-lag increase with an increasing pulse frequency. From the perspective of initial electron generation, the quantitative mathematical relationship between PD characteristics (RPDIV, PD amplitude, PD number, and PD time-lag) and frequency was established based on the Fowler–Nordheim field emission effect for the first time, which can reflect the influence of frequency on the memory effect and the development process of PD. The results can provide an experimental basis and a mechanistic explanation for the evaluation of PD characteristics for film capacitors under nanosecond pulse voltage. [ABSTRACT FROM AUTHOR]

Pulsed electric field-induced electroporation has been widely used, but its specific perforation theory has not been fully elucidated. Therefore, this Perspective paper takes as a clue the dynamic development relationship between the pore energy and the pore state in cell membranes. First, based on the contribution of line tension, surface tension, steric repulsion, and applied electric field to pore energy, the theoretical models of reversible electroporation of a microsecond pulsed electric field and irreversible electroporation of a high-frequency nanosecond pulsed electric field are reviewed. Then, the contribution of elastic strain energy to pore energy is increased, and the theoretical model of pulsed electric field electroporation considering the mechanical properties of cell membranes is further reviewed. Based on the contribution of magnetic stress generated by the magnetic field and the gradient magnetic field to pore energy, a theoretical model of cell membrane magnetoporation under the action of a pulsed magnetic field is proposed, which lays a theoretical foundation for the popularization and application of non-contact cell membrane perforation technology. [ABSTRACT FROM AUTHOR]

Conductive polymer composites require high conductive filler loadings to achieve relatively ideal electromagnetic interference (EMI) shielding performance, which brings problems such as heavy weight and poor processability and ultimately limits their application in the aerospace field. To solve the above problems and realize the preparation of excellent EMI shielding composites with low filler loadings, a bipolar pulsed electric field-induced graphene nanoplatelets (GNPs) alignment method is proposed in this paper to improve the electrical conductivity and EMI shielding performance. The orientation and alignment of GNPs in the matrix were characterized by x-ray diffraction and scanning electron microscopy, and the results showed that GNPs formed a conductive network. The electrical conductivity of the composite material in the X-band was measured, and the results showed that the bipolar pulsed electric field could significantly improve the electrical conductivity of the composite material; the improvement percentage reached 100%–300% under the five filler loadings. In addition, the EMI shielding effectiveness of the composite material in the X-band was tested. The results showed that the EMI shielding effectiveness of the composite material with a mass fraction of 14% increased from 16.48–15.86 dB to 21.37–20.99 dB with the action of the bipolar pulsed electric field, and the improvement percentage was 32%. This is the first study on improving the EMI shielding performance of composite materials by applying a bipolar pulsed electric field, and it provides an effective method to prepare EMI shielding composites with low filler loadings. [ABSTRACT FROM AUTHOR]

The mechanical properties of the cell membrane play an important role in electroporation. This paper studied the influence of the mechanical properties of the cell membrane on the transition energy of electroporation through both modeling and experiments. An electromechanical coupling model of a single pore on the cell membrane was established in COMSOL, and the effect of elastic strain energy on the formation of pores was analyzed. Additionally, to compare the transition energy barrier of pores for different elastic properties of the cell membrane, electroporation experiments were carried out at different temperatures. The simulation showed that the elastic strain energy of the cell membrane increased the transition energy barrier of the pores. The experiments also showed that the transition energy barrier was larger when the elasticity of the cell membrane is intact, which was in good agreement quantitatively with the simulation results. We demonstrated that the mechanical properties of the cell membrane hinder the pore formation, which may be due to the increase of the transition energy barrier. We analyzed the possible mechanism of the effect of cell membrane mechanical properties on electroporation and found the contribution of cell membrane mechanical properties to electroporation during the delivery of exogenous substances, which can provide guidance for improving therapies in electrochemotherapy. [ABSTRACT FROM AUTHOR]

Nanosecond pulsed electric fields over 200 kV/mm have been used for filler alignment in polymer-based thin film (120–250 μm) composites to improve their thermal conductivity, but little research has been performed on bulk composites because of the requirement of an extremely high nanosecond pulsed voltage. In this paper, a microsecond pulsed voltage with a pulse width of 1 μs and an electric field of only 11.76 kV/mm was adopted for the first time to prepare bulk composites of 1.7 mm. The effects of frequency on nanosheets' orientation and the thermal conductivity of epoxy composites were studied. The orientation degree of BN nanosheets was determined based on cross-sectional scanning electron microscopy images and X-ray diffraction peaks. The orientation degree and thermal conductivity of epoxy composites increased with the increase of the frequency, but the increase rate was lower under higher frequencies. The thermal conductivity of composites containing 10 wt. % BN nanosheets prepared under 100 Hz was 0.588 W/mK, which was more than twice that of composites without an applied electric field. Additionally, an effective medium theory model was adopted for thermal conductivity modeling. In addition, thermogravimetric and differential scanning calorimetry analyses were performed to evaluate the thermal properties of the composites. The results showed that after BN orientation in epoxy resin, the composites had higher glass transition temperature and better thermal stability. Microsecond pulsed electric fields are promising for preparing bulk insulation composites with higher thermal conductivity. [ABSTRACT FROM AUTHOR]

Axial magnetostriction of Terfenol-D oriented crystals is highly anisotropic when changing the magnetization direction. Magnetostrictions of a <110> oriented crystal Tb0.36Dy0.64(Fe0.85Co0.15)2 were investigated under magnetic fields with a series of angles θ to its axis. Totally different anisotropic magnetostrictive behaviors are observed after annealing under a coaxial field of 240 kA/m. The magnetostriction for the field annealed specimen seems unsaturated even under 640 kA/m for angles θ in the range from 0° to 55°. At these angles, magnetostriction “ascending” is observed during the final magnetization process, while magnetostriction “dropping” occurs at angles above 35° for the untreated crystal. With the increase in angle θ, the corresponding field where magnetostriction starts dropping decreases for the untreated crystal, while the field at which magnetostriction starts ascending increases for the field annealed one. A simplified model based on moment “jump” and “rotation” is proposed to explain such anisotropic behaviors. [ABSTRACT FROM AUTHOR]

Several analyses are conducted to explain the anisotropic magnetorestriction exhibited by the oriented crystal [Tb.sub.0.36][Dy.sub.0.64][([Fe.sub.0.85][Co.sub.0.15]).sub.2] compound. The impact of the angle on the corresponding field on the corresponding field of magnetorestriction is also analyzed.

The magnetic force microscopy technique is employed to explain the structures and properties of the various magnetically annealed [Tb.sub.0.36][Dy.sub.0.64][([Fe.sub.0.85][Co.sub.0.15]).sub.2] polycrystals. Field annealing is shown to completely change the initial magnetic states of the crystals.

Totally different stress dependences of magnetization and magnetostriction are observed in oriented [Tb.sub.0.36][Dy.sub.0.64][([Fe.sub.0.85][Co.sub.0.15]).sub.2] polycrystals after perpendicular magnetic annealing. The variation in the magnetization is contributed by the redistribution of initial magnetic moments and enlargement of wall energy.

The magnetic and magnetotransport properties of the polycrystalline ErMn6Sn6 compound in the temperature interval of 5-380 K are explored. Positive magnetoresistance (MR) is displayed by ErMn6Sn6 in the ferrimagentic state and a negative MR is displayed in the antiferromagentic state.

Magnetic transitions and magnetoresistance (MR) effect of the HfFe6Ge6 -type Y0.7Ce0.3Mn6Sn6 compound have been investigated in the temperature range of 5-370 K. It is found that the MR behavior of the sample can be expressed as MR = -A(M/M(sub s))(super 2) in the field range from antiferromagnetic to ferrimagnetic configuration, and the power-law magnetic-field dependence of the MR effect is shown in the ferrimagnetic state.

Effects of Tb substitution for Er on the magnetic and transport properties of the Er0.9Tb0.1Mn6Sn6 compound are discussed. Er0.9Tb0.1Mn6Sn6 displays several magnetic phases, such as paramagnetic, ferrimagnetic, and antiferromagnetic, indifferent temperature ranges.

Magnetic force microscopy (MFM) is used to study the domain structures on both transverse and longitudinal sections of Tb0.36Dy0.64(Fe0.85Co0.15)2<110> oriented polycrystals, which were annealed in a magnetic field of 0.3 T. Different MFM patterns were observed after either perpendicular or parallel field annealing, suggesting that the magnetization of each domain rotates when cooling through their Curie temperature. The long axes of most domains tend to align parallel to the annealing field direction. It gives direct evidence to show the change in the initial magnetic states induced by field annealing, which should be responsible for the variation in the magnetoelastic properties [ABSTRACT FROM AUTHOR]