Search

Wide bandgap (WBG) semiconductor devices are developing rapidly due to their superior performance compared to traditional silicon-based devices. However, the packaging technology of traditional devices has limited the application of WBG semiconductor devices because of the challenges in electrical insulation. The complex environment of high blocking voltage, high frequency, and high temperature is the major reason for insulation failure of encapsulation structure. Therefore, in this article, an epoxy resin composite with nonlinear conductivity is proposed to be used as a coating to improve the electric field distribution of high-voltage high-power IGBT modules. First, an electrical field simulation model was built considering the thermal stress. It was found that the electric field in high temperature was improved compared with that in room temperature due to the temperature-dependent conductivity of silicone gel. Nevertheless, the risk of insulation failure still exists. After the application of nonlinear conductivity materials (NCMs) coating, the maximum electric field at the triple junctions and the ratio of electric field distortion in high field areas were significantly decreased. Further analysis showed that the optimization ratio of electric field increased with the increase of the blocking voltages or power losses in the IGBT chip. The results have demonstrated that the NCMs can reduce the maximum electric field in the IGBT encapsulation structure by 73% under the operating conditions of 120 W 10 kV. Partial discharge (PD) tests show that the partial discharge initial voltage (PDIV) of the substrates with NCM coating is increased by 33% compared with the normal encapsulation structure and the coating significantly inhibits the growth of electric trees. The presented results indicate that the NCMs have the potential to improve the insulation performance of high-voltage high-power IGBT modules. [ABSTRACT FROM AUTHOR]

According to the characteristics of an actual electromagnetic rail launcher (EMRL), this article points out defects in the traditional dynamic response model of EMRL, proposes an improved dynamic response model, and analyzes its dynamic and stopping response characteristics. On this basis, it presents a fast and accurate numerical calculation method for three-dimensional transient electromagnetic (EM) force of the EMRL and an order-reduced model of EMRL dynamic response. Furthermore, the second development of commercial software leads to the establishment of an interior ballistic simulation model with EM-structural coupling. The model is used to analyze the interior ballistic characteristics of the EMRL under sequential discharge and continuous firing. The finding is that the dynamic response of the first launching rail will cause a deformation in the second launching rail, in which a greater fluctuation happens. When the time interval between successive launches reaches 1.0 s, the deformation of the second launching rail will no longer be affected by the dynamic response of the first launching rail. [ABSTRACT FROM AUTHOR]

In noncooperative bistatic synthetic aperture radar (SAR), the position of the transmitter's beam footprint should be detected and tracked in real time to perform beam synchronization. Theoretical analysis shows that the signal-to-noise ratio (SNR) of the reflected signals from the observational scene is too low to apply the conventional detection and tracking method. According to the cross correlation and Doppler frequency information of the raw data, a transmitter's beam footprint detection and tracking method is proposed in this paper. This method can realize the beam footprint detection in the sidelobe of the receiver's beam footprint and obtain the relative position between the transmitter and the receiver, therefore significantly improve the performance of beam footprint detection and tracking in noncooperative. Meanwhile, vehicle-based bistatic SAR experiment and airborne bistatic SAR experiment are performed to evaluate the performance of the proposed transmitter's beam footprint detection and tracking method. Experimental results show that the proposed method performs well for real-time transmitter's beam footprint detection and tracking. [ABSTRACT FROM PUBLISHER]