Avalanche Testing Research Articles

Avalanche capability degradation of the parallel-connected SiC MOSFETs

Silicon carbide (SiC) MOSFET chips are often connected in parallel in a module to increase the current rating. However, the current capability is degraded due to unbalanced current and temperature distributions which affect the avalanche processes particularly in extreme operating conditions. To obtain the root cause of the degradation and identify the dominant factors, single-pulse avalanche testing is carried out in this study, and TCAD simulation is used for mechanism analysis. It is revealed that electrothermal parameters have different effects on current sharing in different stages of avalanching. The corresponding failure mechanisms are analyzed, and the main cause of avalanche failure with parallel devices is found to be the difference in breakdown voltage. Device with smaller BV shares more current as well as more heat, which fails first eventually. To resolve such issues, proper device screening/paring should be carried out. The findings are helpful for a better understanding of avalanche capability degradation in parallel devices application.

Avalanche testing: towards the next generation of particle detectors

Avalanche testing: towards the next generation of particle detectors

Introduction of the energy to break an avalanche as a promising parameter for powder flowability prediction

Dynamic avalanche testing is a newer method useful even with cohesive powder samples. To evaluate flow properties of pharmaceutical powder excipients, break energy (BE) is introduced as a new promising avalanche parameter. Conventional pharmacopoeial methods and an annular shear cell were utilized to characterize 23 pharmaceutical powder samples including binary mixtures. Subsequently, rotating drum avalanching was studied to better understand behaviour of powders. A good linear regression between the energy to break a powder avalanche and powder cohesion with R2 = 0.823 was detected. The relationship between BE and the flow function value, estimated by shear testing, allowed to identify two samples with excellent flow functions: Cellets 100 and Neusilin US2. The latter sample also had very low BE although the mass flow rate was the poorest observed out of 23 samples. Therefore, the BE from avalanching testing seems to be a sensitive measure of cohesion and flow function behaviour.

3D projection and multivariate image analysis for quantitative visual modelling of mixability and rheological behavior of lactose powder

BackgroundThis study reports the use of multivariate time and image analysis of avalanche videographic data for quantitative visual modelling of mixability. Its usefulness, in mechanistically modelling a powder’s rheological behavior in relation to mixing, was evaluated. MethodsParticle size distribution (PSD) of a pharmaceutical grade lactose powder was modified to reflect commercially encountered variability. The PSD variants were rheologically distinct and had different mixability. Avalanche testing was performed on the modified lactose powders. Avalanche rheological properties (ARP) profiles and videos were collected for numerical and quantitative visual modelling, respectively. In quantitative visual modelling, videos captured were transformed into serial projected images. Important features of the projected images were extracted as eigen-images, to derive the avalanche rheological visual metric (ARVM). Mixability was modelled as a function of ARP or ARVM and the rotation speed. ResultsRelative to the ARP model, the ARVM models were highly interpretable. As a univariate expression of ARP, ARVM also possessed construct validity (r2 greater than 0.99, slope ≥ 0.96). Important rheological features of the lactose powders were holistically visualized within a single eigen-image which enabled the generation of simpler models (5 versus 34 variables for ARP model). The ARVM models predicted mixability of lactose powders with greater accuracy than the ARP model (relative root mean square error of external validation ≤ 3.30% versus 4.96%). ConclusionsQuantitative visual modelling is a viable alternative to purely numerical approaches. Most significantly, the model’s interpretability and concreteness enable manufacturers to readily understand the risk posed by PSD variability on manufacturing processes and swiftly take pre-emptive actions, without being mired in multivariate data complexity. In addition, the use of quantitative visual approach in time series imaging, for studying and monitoring industrial processes, could also be explored.

On the development of powder spreadability metrics and feedstock requirements for powder bed fusion additive manufacturing

Existing powder feedstock metrics for powder bed fusion (PBF) additive manufacturing (AM) are related to packing efficiency and flowability, and newer techniques, such as powder rheometry and dynamic avalanche testing, have received recent attention in the literature. To date, however, no powder characterization technique is able to predict the spreadability of AM feedstock. In fact, no such spreadability metrics exist. This study endeavored to establish viable powder spreadability metrics through the development of a spreadability testing rig that emulates the recoating conditions present in commercial PBF AM systems. As no metrics for spreadability currently exist, four potential metrics were evaluated in a 3∙23 split plot experimental design. These four metrics were: (1) the percentage of the build plate covered by spread powder, (2) the rate of powder deposition, (3) the average avalanching angle of the powder, and (4) the rate of change of the avalanching angle. Three samples of gas atomized, Al-10Si-0.5 Mg PBF powder representing differing degrees of quality were used as the levels of the powder quality input variable. As no powder quality metrics have been shown to be indicative of powder spreadability in PBF, various bulk powder characteristics were used as the powder quality indicator during ANOVA. Of the four metrics tested, the average avalanching angle, while statistically dependent of the powders angle of repose, showed poor correlation with experimental data. The remaining three metrics, however, were all found to have a statistically significant dependence on the angle of repose. Increasing the angle of repose resulted in significantly worse powder spreading, i.e. poor build plate coverage and powder clumping, as measured by the viable spreading metrics. Other processing parameters, such as the recoating speed and the recoater blade material were shown to also influence the spread quality.

Investigating the effect and mechanism of particle size distribution variability on mixing using avalanche testing and multivariate modelling

Particle size distribution (PSD) variability in excipients is widely thought to affect the mixing process and the achievement of blend homogeneity. Yet, few studies have addressed this issue by attempting to ascertain the relationship and elucidate its mechanism. To address this, the model material, lactose, was modified to reflect commercially relevant PSD variations and mixed with microcrystalline cellulose and chlorpheniramine in a double-cone blender. Multivariate modelling and avalanche testing were applied to elucidate the relationship and mechanism. PSD variability can cause significant change in mixing time, by 8 times and 3 times (p ≈ 0.00) for high and low dose drug formulations, respectively. Achievement of blend homogeneity depended on the dispersive mixing mechanism (r2 = 0.99). Dispersive mixing was adversely affected by powder cohesiveness and powder dilation, which increased as the proportion of fine particles in lactose powder increased. This study yielded three conclusions. Firstly, PSD variability in pharmaceutical grade excipients can cause unacceptable prolongation in mixing time. Secondly, the impact of PSD variability on continuous mixing and other batch mixing of various scales, requires investigation. Lastly, the current findings can contribute to the development of robust mixing operations in the form of offline pre-emptive measures and inline process control strategies.

Avalanche Capabilities of Commercial 1200 V 4H-SiC Power MOSFETs

Avalanche testing is a common method for evaluating the ruggedness of switching devices. Typically, datasheets specify an avalanche rating under a single operating condition. Instead, in this work, 1.2 kV, 24 A SiC MOSFETs are subjected to avalanche events under a variety of conditions. From this testing, a curve is drawn which shows the area for safe avalanche operation. Post-characterization and high temperature reverse bias testing were performed to ensure that the avalanche events did not degrade the device performance or lifetime. CoolMOS devices were also tested for comparison, and, unlike the SiC MOSFETs, the Si devices showed a notable decrease in avalanche capability as the current in avalanche was increased. The SiC MOSFETs were able to endure one hundred single avalanche events at 20 A and 1000 mJ without any sign of lifetime degradation.

Flowability characterisation of drug–excipient blends using a novel powder avalanching method

The scope of the work is twofold, first to introduce a new avalanche testing instrument and secondly to characterise flowability of pharmaceutical blends comprising of coarse and fine particles. The results were compared with established powder characterisation instruments like the angular shear cell and a flow through orifice tester. These different methods were applied to a broad concentration range of binary mixtures comprising coarse, well-flowing lactose and micronised, poorly flowing albendazole. Some of the mixtures were further analysed with scanning electron microscopy. The results showed clear changes in the flow behaviour of the mixtures that were considered as critical flow concentrations (CFCs). At least three drug concentrations were observed for which the flow behaviour essentially changed. Accordingly, different flow regions were identified, which were explained on the basis of changed particle packing configurations. A theoretical model successfully provided a first estimation of the initial two CFCs. In conclusion, the novel avalanche testing instrument provided complementary information to conventional flowability methodologies, and a thorough assessment of pharmaceutical blends is needed to avoid CFCs in view of a robust formulation development and hence with respect to building quality into the design of the solid dosage forms.

Optimizing tape‐burnishing/wiping process of magnetic recording media through Taguchi method

AbstractFor the ever‐increasing recording density in hard disk drives, ultra‐low gliding height media are required. It is an immense challenge for the tape‐burnishing/wiping process of media to reduce the asperities effectively and efficiently while no scratches occur. The purpose of this paper is to characterize and then optimize the tape‐burnishing/wiping process as so to minimize the asperities without leaving any scratches on the media surface. A Taguchi experiment design method is adopted to analyze the data and acquire an optimal level combination of process parameters. The resulting optimal combination is practically implemented in tape‐burnishing/wiping the several magnetic recording media, which reveals that the average pass ratio of 5 nm glide avalanche testing increases nearly doubly to a level of 96%. Copyright © 2008 John Wiley & Sons, Ltd.

Development of a robust procedure for assessing powder flow using a commercial avalanche testing instrument

The objectives of this work were to develop a robust procedure for assessing powder flow using a commercial avalanche testing instrument and to define the limits of its performance. To achieve this a series of powdered pharmaceutical excipients with a wide range of flow properties was characterized using such an instrument (Aeroflow, TSI Inc., St. Paul, MN, USA). The experimental conditions (e.g., sample size, rotation speed) were rationally selected and systematically evaluated so that an optimal standard-operating-procedure could be identified. To evaluate the inherent variability of the proposed methodology samples were tested at multiple sites, using different instruments and operators. The ranking of the flow properties of the powders obtained was also compared with that obtained using a conventional shear-cell test. As a result of these experiments a quick, simple, and rugged procedure for determining the flow properties of pharmaceutical powders in their dilated state was developed. This procedure gave comparable results when performed at four different testing sites and was able to reproducibly rank the flow properties of a series of common pharmaceutical excipient powders. The limits of the test method to discriminate between different powder samples were determined, and a positive correlation with the results of a benchmark method (the simplified shear cell) was obtained.

The design of laser texture media using acoustic emission measurements

Investigates the flying and contact phenomena of proximity contact recording and flying sliders. The tribological performance of thin film laser textured media is studied with acoustic emission analysis. The laser bump height and density were controlled to achieve a desired tribological performance. The relationship between the laser bump height/density and acoustic emission energy during drag and start/stop testing for different slider designs was studied. Emphasis was also placed on identifying the critical parameters of media and slider designs for tribological performance improvements. Reliability and glide height avalanche testing results were found to correlate well with the acoustic emission energy data.

Glide characteristics of a laser textured disk

Irregular peak signals were observed during the glide height avalanche testing of a laser textured disk. Those peak signals were analyzed and found to be consistent with the first ringing frequency of the slider vibration. The frequencies were also found to be mathematically related to the bump spacing and some specific slider speed where the irregular peaks located, and subsequently the frequencies can be calculated.