Evaluation of high temperature dielectric films for high voltage power electronic applications

Three high temperature films, polyimide, Teflon perfluoroalkoxy and poly-P-xylene, were evaluated for possible use in high voltage power electronic applications, such as in high energy density capacitors, cables and microelectronic circuits. The dielectric properties, including permittivity and dielectric loss, were obtained in the frequency range of 50 Hz to 100 kHz at temperatures up to 200°C. The dielectric strengths at 60 Hz were determined as a function of temperature to 250°C. Confocal laser microscopy was performed to diagnose for voids and microimperfections within the film structure. The results obtained indicate that all films evaluated are capable of maintaining their high voltage properties, with minimal degradation, at temperatures up to 200°C. However, above 200°C, they lose some of their electrical properties. These films may therefore become viable candidates for high voltage power electronic applications at high temperatures.     

Effect of high energy electron radiation on MIPB-impregnatedpolypropylene film

The effect of impregnating capacitor-grade polypropylene film with an aromatic hydrocarbon fluid is examined with a view towards assessing the response under radiation of the relevant properties of the film. Monoisopropyl biphenyl (MIPB)-impregnated polypropylene film was exposed in air to 1-MeV electrons at different dose rates and the post-radiation effects on the electrical, mechanical, morphological, and chemical properties were evaluated. The results obtained indicate that the oil-impregnated films remain relatively stable even at the highest dose of 10⁸ rads. This is in contrast to the results reported by the authors (ibid., vol.NS-34, no.6, p.1822-6, 1987) for dry polypropylene films which underwent degradation due to chain scission and oxidation. In the present instance, it is believed that impregnation of the film has inhibited the diffusion of oxygen and consequently favored crosslinking. The chemical characterizations as well as the changes in some of the measured properties of the film are seen to corroborate this belief     

Effect of ionizing radiation on the electrical characteristics ofpolyvinylidene fluoride (PVF2)

The influence of high-energy electron irradiation on the electrical properties of biaxially oriented polyvinylidene fluoride (PVF ₂) film was investigated. The film was irradiated in air with a 1-MeV electron beam at a dose rate of 10⁶ rad/min to different dose levels of up to 10⁸ rad. Electrical properties measured included dielectric permittivity and dielectric loss, AC and DC breakdown voltages, and DC volume resistivity, X-ray diffraction and IR spectroscopy measurements were also made. The most pronounced of the radiation-induced changes were a decrease in like AC breakdown voltage and an increase in dielectric loss, both corresponding to increasing total absorbed dose. DC breakdown voltage and volume resistivity also showed noticeable changes. These changes are believed to be associated initially with a radiation-induced crystal phase transformation. This was confirmed by the X-ray diffraction curve and the IR spectra, which showed an increase in the β-phase and a decrease in the α-phase peaks at higher dose levels     

A novel pilot-scale production of fuel gas by allothermal biomass gasification using biomass micron fuel (BMF) as external heat source

A novel pilot-scale allothermal biomass gasification system integrating steam gasification, thermal cracking, and catalytic reforming aiming at fuel gas production was developed. Biomass micron fuel (BMF) was used as external heat source by combusting with air in the combustor. Biomass feedstock was gasified with steam, and then, tar in the produced gas was decomposed by thermal cracking and catalytic reforming. The waste heat of high-temperature flue gas and fuel gas was recovered and used for biomass feedstock pre-heating and steam generation, respectively. The fuel gas yield is 1.36 Nm³/kg with lower heating value of 11.61 MJ/Nm³. An overall energy analysis of the system was also investigated. The results showed that the cold gas efficiency and energy conversion efficiency in this system are 88.11 and 63.59 %, respectively. Meanwhile, combustion of BMF accounts for 25.66 % of the total energy input.     

Effects of multistress aging (radiation, thermal, electrical) onpolypropylene

Capacitor-grade polypropylene films were aged under multiple stresses (electrical, thermal, and radiation). The aging experiments were performed for both singular and simultaneous combined stresses. The polypropylene was exposed to combined neutron-gamma radiation with a total dose of 1.6×10⁶ rad, electrical stress at 40 V _rms/μm, and thermal stress at 90°C. Post-aging diagnostics consisting of electrical, mechanical, physical and chemical characterization were carried out to identify degradation mechanisms for polypropylene films under multifactor stress aging. The most pronounced changes were observed in the mechanical properties of the film. Significant decrease in elongation at break and tensile strength proved deterioration of the polypropylene under combined neutron-gamma radiation. This decrease was caused by chain-scission of the polypropylene molecules. The temperature stress had an opposite effect, causing an increase in the above-mentioned properties and offsetting, therefore, the negative effect of radiation. Although changes were observed in the electrical properties, they were not as significant as those for the mechanical characteristics. It can be concluded, that the failure mechanism of the electrical insulation under multistress aging conditions could be a mechanical failure of the material, rather than direct homogeneous decay in the dielectric strength or thermal breakdown of the polymer     

IPM-Model: AI and metaheuristic-enabled face recognition using image partial matching for multimedia forensics investigation with genetic algorithm

The rapid enhancement in the development of information technology has driven the development of human facial image recognition. Recently, facial recognition has been successfully applied in several distinct domains with the help of computing and information technology. This kind of application plays a significant role in the process of digital forensics investigation, recognizing the patterns of a human face based on the partial matching of images that would be in 24-bit color image format, including the spacing of the eyes, the bridging of the nose, the contour of the lips, ears, and chin. In this paper, we have proposed and implemented an image recognition model based on principal component analysis, genetic algorithms, and neural networks, in which PCA reduces the dimension of the benchmark dataset, while genetic algorithms and neural nets optimize the searching patterns of image matching and provide highly efficient output with a minimal amount of time. Through the experiment results on the human facial images dataset of the Georgia Institute of Technology, the overall match showed that the proposed model can achieve the recognition of human face images with an accuracy rate of 93.7%. Moreover, this model helps to examine, analyze, and detect individuals by partial matching with reidentification in the procedure of forensics investigation. The experimental result shows the robustness of the proposed model in terms of efficiency compared to other state-of-the-art methods.

     

Characterization of electron-irradiated biaxially-orientedpolypropylene films

Post-radiation changes in the electrical and mechanical properties of capacitor-grade isotactic polypropylene films exposed to electron radiation were previously reported by the authors (ibid., vol.NS-34, no.6, p.1822-6, Dec. 1987). Based on the data obtained, it was suggested that crosslinking, chain scission and oxidative degradation were responsible for the radiation-induced changes in the film. In the present investigations, additional electrical characterizations that included the DC breakdown voltage and AC conductivity measurements were performed. Effects of the electron radiation on the physical and chemical properties were also evaluated to identify the actual degradation mechanisms. These studies included scanning electron microscopy, X-ray diffraction, infrared spectroscopy and sol-gel measurements. The results obtained confirm that crosslinking and chain scission of the polymer are responsible for the changes in the lower dose range, whereas oxidative degradation becomes predominant at higher dose levels