Epoxy resin is widely used in the support,insulation,and packaging components of electrical equipment owing to their excellent insulation,thermal,and mechanical properties.However,epoxy-resin insulation often suffers ...Epoxy resin is widely used in the support,insulation,and packaging components of electrical equipment owing to their excellent insulation,thermal,and mechanical properties.However,epoxy-resin insulation often suffers from thermal and mechanical stresses under extreme environmental conditions and a compact design,which can induce electrical tree degradation and insulation failure in electrical equipment.In this study,the photoelastic method is employed to investigate the thermal-mechanical coupling stress dependence of the electrical treeing behavior of epoxy resin.Typical electrical tree growth morphology and stress distribution were observed using the photoelastic method.The correlation between the tree length and overall accumulated damage with an increase in mechanical stress is determined.The results show that compressive stress retards the growth of electrical trees along the electric field,while tensile stress has accelerating effects.This proves that the presence of thermal stress can induce more severe accumulated damage.展开更多
The electric field stress applied to the cell in the electric field will cause the biological effects of the cell on electromagnetic field. In this paper, the single-shell spherical cell is equated to dielectric spher...The electric field stress applied to the cell in the electric field will cause the biological effects of the cell on electromagnetic field. In this paper, the single-shell spherical cell is equated to dielectric spheres, and a biophysical method is used to solve the boundary value problem, and then Maxwell tensor analysis is used to discuss the electric field stresses affecting the applied electric field applied to the cells. The results of numerical analysis show that the ion mobility decreases nonlinearly with increasing frequency in the lower region of the applied electric field frequency, and increases with increasing equivalent dielectric constant at a certain frequency, and the magnitude of the electric field stress is almost independent of the frequency;as the frequency increases, the ion mobility tends to a minimum value and is almost independent of the equivalent dielectric constant, while the applied electric field frequency and the cell dielectric constant both affect the cell normal and the tangential stresses. Therefore, the frequency applied electric field and cell dielectric constant affect the extracellular ion mobility, electric field stress applied to the cell membrane by the electric field;the extracellular ion mobility caused by the electric field in the low frequency range is more pronounced than that in the high frequency, and electric field stress is the basic cause of cell deformation.展开更多
In spite of their extraordinary performance, AlGaN/GaN high electron mobility transistors （HEMTs） still lack solid reliability. Devices under accelerated DC stress tests （off-state, VDS = 0 state, and on-state step...In spite of their extraordinary performance, AlGaN/GaN high electron mobility transistors （HEMTs） still lack solid reliability. Devices under accelerated DC stress tests （off-state, VDS = 0 state, and on-state step-stress） are investigated to help us identify the degradation mechanisms of the AlGaN/GaN HEMTs. All our findings are consistent with the degradation mechanism based on crystallographic-defect formation due to the inverse piezoelectric effects in Ref. [1] （Joh J and del Alamo J A 2006 IEEE IDEM Tech. Digest p. 415）. However, under the on-state condition, the devices are suffering from both inverse piezoelectric effects and hot electron effects, and so to improve the reliability of the devices both effects should be taken into consideration.展开更多
基金Supported by the National Natural Science Foundation of China(52377153)and Science and Technology Project of Hebei Education Department(QN2023073).
文摘Epoxy resin is widely used in the support,insulation,and packaging components of electrical equipment owing to their excellent insulation,thermal,and mechanical properties.However,epoxy-resin insulation often suffers from thermal and mechanical stresses under extreme environmental conditions and a compact design,which can induce electrical tree degradation and insulation failure in electrical equipment.In this study,the photoelastic method is employed to investigate the thermal-mechanical coupling stress dependence of the electrical treeing behavior of epoxy resin.Typical electrical tree growth morphology and stress distribution were observed using the photoelastic method.The correlation between the tree length and overall accumulated damage with an increase in mechanical stress is determined.The results show that compressive stress retards the growth of electrical trees along the electric field,while tensile stress has accelerating effects.This proves that the presence of thermal stress can induce more severe accumulated damage.
文摘The electric field stress applied to the cell in the electric field will cause the biological effects of the cell on electromagnetic field. In this paper, the single-shell spherical cell is equated to dielectric spheres, and a biophysical method is used to solve the boundary value problem, and then Maxwell tensor analysis is used to discuss the electric field stresses affecting the applied electric field applied to the cells. The results of numerical analysis show that the ion mobility decreases nonlinearly with increasing frequency in the lower region of the applied electric field frequency, and increases with increasing equivalent dielectric constant at a certain frequency, and the magnitude of the electric field stress is almost independent of the frequency;as the frequency increases, the ion mobility tends to a minimum value and is almost independent of the equivalent dielectric constant, while the applied electric field frequency and the cell dielectric constant both affect the cell normal and the tangential stresses. Therefore, the frequency applied electric field and cell dielectric constant affect the extracellular ion mobility, electric field stress applied to the cell membrane by the electric field;the extracellular ion mobility caused by the electric field in the low frequency range is more pronounced than that in the high frequency, and electric field stress is the basic cause of cell deformation.
基金Project supported by the National Basic Research Program of China (Grant No. 2011CBA00600)the National Natural Science Foundation of China (Grant No. 61106106)the Fundamental Research Funds for the Central Universities (Grant No. K50510250006)
文摘In spite of their extraordinary performance, AlGaN/GaN high electron mobility transistors （HEMTs） still lack solid reliability. Devices under accelerated DC stress tests （off-state, VDS = 0 state, and on-state step-stress） are investigated to help us identify the degradation mechanisms of the AlGaN/GaN HEMTs. All our findings are consistent with the degradation mechanism based on crystallographic-defect formation due to the inverse piezoelectric effects in Ref. [1] （Joh J and del Alamo J A 2006 IEEE IDEM Tech. Digest p. 415）. However, under the on-state condition, the devices are suffering from both inverse piezoelectric effects and hot electron effects, and so to improve the reliability of the devices both effects should be taken into consideration.
