Silicon-Carbide Power MOSFET Performance in High Efficiency Boost Power Processing Unit for Extreme Environments

Silicon-Carbide device technology has generated much interest in recent years. With superior thermal performance, power ratings and potential switching frequencies over its Silicon counterpart, Silicon-Carbide offers a greater possibility for high powered switching applications in extreme environment. In particular, Silicon-Carbide Metal-Oxide- Semiconductor Field-Effect Transistors' (MOSFETs) maturing process technology has produced a plethora of commercially available power dense, low on-state resistance devices capable of switching at high frequencies. A novel hard-switched power processing unit (PPU) is implemented utilizing Silicon-Carbide power devices. Accelerated life data is captured and assessed in conjunction with a damage accumulation model of gate oxide and drain-source junction lifetime to evaluate potential system performance at high temperature environments

Long-Term Reliability of a Hard-Switched Boost Power Processing Unit Utilizing SiC Power MOSFETs

Silicon carbide (SiC) power devices have demonstrated many performance advantages over their silicon (Si) counterparts. As the inherent material limitations of Si devices are being swiftly realized, wide-band-gap (WBG) materials such as SiC have become increasingly attractive for high power applications. In particular, SiC power metal oxide semiconductor field effect transistors' (MOSFETs) high breakdown field tolerance, superior thermal conductivity and low-resistivity drift regions make these devices an excellent candidate for power dense, low loss, high frequency switching applications in extreme environment conditions. In this paper, a novel power processing unit (PPU) architecture is proposed utilizing commercially available 4H-SiC power MOSFETs from CREE Inc. A multiphase straight boost converter topology is implemented to supply up to 10 kilowatts full-scale. High Temperature Gate Bias (HTGB) and High Temperature Reverse Bias (HTRB) characterization is performed to evaluate the long-term reliability of both the gate oxide and the body diode of the SiC components. Finally, susceptibility of the CREE SiC MOSFETs to damaging effects from heavy-ion radiation representative of the on-orbit galactic cosmic ray environment are explored. The results provide the baseline performance metrics of operation as well as demonstrate the feasibility of a hard-switched PPU in harsh environments

Design and optical characterization of gallium arsenide aluminum arsenide material system reflective modulators for mid-infrared free space optical applications using solid-source molecular beam epitaxy

With the ever-growing usage of free space optical communication implementations, new innovations are currently being made to help improve the quality of transmission of these systems. One particular method employed to help improve transmission efficiency of optical links is shifting the transmission wavelength into the mid-infrared spectrum. Studies have shown sufficient increase in atmospheric transmission at and around mid-infrared wavelengths (near 3-5 mm). In order to successfully implement such systems at these wavelengths, devices must first be designed that are capable of optical communication operation at such wavelengths. One such device common in modern free space optical systems is the reflective modulator. This device minimizes the pointing and tracking associated with establishing free space optical connections. In this dissertation, a free space optical reflective modulator is designed using Gallium Arsenide and Aluminum Arsenide (GaAs/AlAs) to operate at midinfrared transmission wavelengths. The reflective modulator consists of multiple quantum well modulator (QWM) atop of a distributed Bragg reflector (DBR). The physical device characteristics are analyzed and the device functionality evaluated using optical characterization techniques

Modelling the performance characteristics of four stroke Internal Combustion Renault Engine cycle using MATLAB simulation tool

The trends in Internal Combustion Engine (ICE) cycle is gradually changing due to the quest for optimum performance, efficiency and zero emission level which are often achieved through a series of experimental procedures. To reduce the huge experimental cost, time and resources, MATLAB 2018b was employed in the modelling and simulation process of a four stroke internal combustion Renault engine (Mercedes-Benz 250SE) W108 model. The displaced volume was 4.65x10-4 mm3 (4.65x10-7 cm3) while the minimum volume occupied by the charge was 0.5x10-4 mm3 (5x10-8). Moreover, the maximum velocity occurred at a crank angle of 72º, having a value of 19.65 m/s while the minimum velocity occurred at a crank angle of 288º with a value of 19.65 m/s. However, maximum cylinder pressure of 28 bar was observed at crank angle of 20º, followed by gradual decline up to 0.2 bar at subsequent crank angles of 100, 200, 300º. The results showed that maximum peak pressure between simulated data and experimental data were 5347 and 5320 KPa, while maximum spark pressure in cylinder before combustion between simulated data and experimental data were 1849 and 1730 KPa. In addition, highest crank angle at maximum pressure for simulated and experimental data were 30 and 22º. It has been established that developing mathematical models to simulate IC engine operation cycles can help offset the cost, time and resources required for experimental set up, testing and data acquisition from the engine

Compendium of Single Event Effect Results from NASA Goddard Space Flight Center

We present the results of single event effects (SEE) testing and analysis investigating the effects of radiation on electronics.This paper is a summary of test results

Application of SEM/EDS in fractographic investigation of TIG welded AISI 1020 fusion zones at distinct welding current steps

Higher arc length is a function of increasing welding current (amperage). It increases the intensity of welding heat, thereby, influencing the microstructure and mechanical properties of the welded material. In this this study, fractographical variations in TIG welded AISI 1020 fusion zones at different welding current steps were investigated using Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM/EDS) techniques. The fracture morphologies showed a fibrous appearance indicating ductile fracture with initiation of a river pattern of branching cracks, forming cleavages along the crystals plains and intergranular fracture occurring along the grain boundaries, indicating brittle fracture as a result of stepwise increase in welding current. It was observed that the ultimate tensile strength of the welded samples decreased correspondingly from 583.3 MPa, 540 MPa, 530.7 MPa, 506.7 MPa to 473.3 MPa as the resulting heat input due to welding current increased from 96.14 A, 120 A, 155 A, 190 A to 213 A. This indicated that the lowest welding current (96.14A) produced fusion zone with the highest ductility when compared to other welding currents which produced fusion zones that tended to be brittle as a result of increasing heat inputs. It was observed that fusion zone with the lowest welding current showed the appearance of a fibrous structure produced by stretching of crystals in their lattice during heat application. Micro-hardness on the surface of the welds revealed that hardness increased with increase in welding current. Therefore, proper control measures should be put in place to ensure that welding input parameters are optimum

Hydration Status and Glycemic Indices of Patients with Type 2 Diabetes Mellitus and HIV Comorbidities in South-South Nigeria

Recently there have been an increasing trend of HIV positive patients surviving longer due to increased availability and compliance with antiretroviral therapy. Some of these patients tend to develop type 2 diabetes mellitus (T2DM) as a result of exposure to certain antiretroviral drugs as well as increasing age of the patients. HIV and T2DM could increase the risks of dehydration in these patients. This study was designed to assess the hydration status of patients having HIV and T2DM comorbidities in Akwa Ibom State, South-South Nigeria. In this study 128 participants aged 18 to 59 years were recruited consecutively from December 2023 to May 2024 from designated hospitals in Akwa Ibom state and grouped into normal, diabetic, HIV and diabetic/HIV with each group made up of 32 individuals. Blood samples were taken for on-the-spot blood glucose estimation, glycated haemoglobin, haemoglobin concentration, serum electrolytes, urea and creatinine. Urine was collected for urinalysis. Serum osmolarity and anion gap were calculated. Blood urea nitrogen concentration as well as blood urea nitrogen/creatinine ratio were also determined. The results showed a significantly higher mean chloride level in the normal and diabetic groups compared to others and a higher bicarbonate level in the diabetic group. Urea and creatinine levels were significantly higher in the diabetic and diabetic+HIV groups when compared with others. Serum calcium was significantly higher in the diabetic and HIV groups compared to others. BUN and BUN/creatinine ratio were significantly higher in the diabetic only group compared to others with serum anion gap, osmolarity, FBS/RBS and HBA1C levels being significantly higher in the diabetic group compared to others. It is concluded that T2DM increased the risk of dehydration which is exacerbated by diabetic/HIV comorbidity

Evaluation of induced residual stresses on AISI 1020 low carbon steel plate from experimental and FEM approach during TIG welding process

Induced residual stresses on AISI 1020 low carbon steel plate during Tungsten Inert Gas (TIG) welding process was evaluated in this study using experimental and Finite Element Method (FEM). The temperature range measured from the welding experimentation was 251°C-423°C, while the temperature range measured from the FEM was 230°C-563°C; whereas, the residual stress range measured from the welding experimentation was 144MPa-402Mpa, while the residual range measured from the FEM was 233-477MPa respectively. Comparing the temperature and stress results obtained from both methods, it was observed that the range of temperature and residual stresses measured were not exactly the same due to the principles at which both methods operate but disparities between the methods were not outrageous. However, these values can be fed back to optimization tools to obtain optimal parameters for best practices. Results of the induced stress distribution was created from a static study where the thermal results were used as loading conditions and it was observed that the temperature increased as the von-Mises stress increased, indicating that induced stresses in welded component may hamper the longevity of such component in service condition. Hence, post-weld heat treatment is imperative in order to stress relieve metals after welding operation and improve their service life

Nonlinear and dynamic modeling of stainless steel strands using artificial neural networks [abstract]

Abstract only availableIn this study, artificial neural networks (ANNs) are used to model a collection of acoustic signals that propagate down a stainless steel strand embedded in concrete. The study of acoustic signals in stainless steel strands is important because steel strands are used to strengthen concrete structures such as bridges, walkways, overpasses, buildings, etc. Unfortunately, stainless steel strands are susceptible to corrosion, which can be the source of various catastrophic failures. The acoustic signals are launched, using Electromagnetic Acoustic Transducers (EMATs), in a stainless steel strand that has been mechanically altered to simulate the corrosion process and to monitor the corrosion that has taken place. The information in the acoustic signals has proven to be extremely difficult to evaluate. Therefore, using principal component analysis (a data compression technique) the large dataset, consisting of over 10,000 points, is compressed down to three principle components (PCs). After the appropriate file conversions have taken place, the PCs are fed into an ANN in order to predict the amount of corrosion within the stainless steel strand. The acoustic signals are compressed, modeled, and predicted with up to 91% accuracy. The neural network structure was optimized to allow 10000:3 data compression ration of acoustic signal intensity values to PCs.McNair Scholars Progra

A Modified Real-Time Fault-Tolerant Task Allocation Scheme for Wireless Sensor Networks

In WSNs, the sensor nodes are at risk of failure and malicious attacks (selective forwarding). This may have a profound negative effect when you consider real-time WSNs, making them challenging to deploy. When there is a delay in tasks allocation execution processes in real-time WSNs because of sensor nodes failures, this will cause disastrous consequences if the systems are safety-critical, e.g. aircraft, nuclear power plant, forest fire detection, battlefield monitoring, thus the need to developed a real-time system that is fault-tolerable. This paper developed a modified real-time fault-tolerant task allocation scheme (mRFTAS) for WSNs (wireless sensor networks), using active replication techniques. mRFTAS and RFTAS performance were compared using time of execution of the task, network lifetime and reliability cost. The mRFTAS performance showed an improvement over that of RFTAS when it comes to reducing the time it takes for task execution by 45.56% and reliability cost of 7.99% while prolonging the network lifetime by 36.35%