1.4 kV, 25 A, PT and NPT Trench IGBTs with optimum forward characteristics

In this paper we report the development of 1.4 kV 25 A PT and NPT Trench IGBTs with ultra-low on-resistance, latch-up free operation and highly superior overall performance when compared to previously reported DMOS IGBTs in the same class. We have fabricated both PT and transparent anode NPT devices to cover a wide range of applications which require very low on-state losses or very fast time with ultra-low switching losses. The minimum forward voltage drop at the standard current density of 100A/cm2 was 1.1 V for PT non-irradiated devices and 2.1 V for 16 MRad PT irradiated devices. The non-irradiated transparent emitter NPT structure has a typical forward voltage drop of 2.2 V, a turn-off time below 100 ns and turn-off energy losses of 11.2 mW/cm2 at 125 C. The maximum controllable current density was in excess of 1000A/cm2.

A comparison of different failure assessment methodologies applied to the NESC-1 test

Predictions for a 75x205mm surface semi-elliptic defect in the NESC-1 spinning cylinder test have been made using BS PD 6493:1991, the R6 procedure, non-linear cracked body finite element analysis techniques and the local approach to fracture. All the techniques agree in predicting ductile tearing near the inner surface of the cylinder followed by cleavage initiation. However they differ in the amount of ductile tearing, and the exact location and time of any cleavage event. The amount of ductile tearing decreases with increasing sophistication in the analysis, due to the drop in peak crack driving force and more explicit consideration of constraint effects. The local approach predicts a high probability of cleavage in both HAZ and base material after 190s, while the other predictions suggest that cleavage is unlikely in the HAZ due to constraint loss, but likely in the underlying base material. The timing of this event varies from ∼150s for R6 predictions to ∼250-300s using non-linear cracked body analysis.

MOS and bipolar gated thyristor: A thyristor with IGBT switching characteristics

The IGBT has become the device of choice in many high-voltage-power electronic applications, by virtue of combining the ease of MOS gate control with an acceptable forward voltage drop. However, designers have retained an interest in MOS gated thyristor structures which have a turn-off capability. These offer low on-state losses as a result of their latching behaviour. Recently, there have been various proposals for dual-gate devices that have a thyristor on-state with IGBT-like switching. Many of these dual gated structures rely on advanced MOS technology, with inherent manufacturing difficulties. The MOS and bipolar gated thyristor offers all the advantages of dual gated performance, while employing standard IGBT processing techniques. The paper describes the MBGT in detail, and presents experimental and simulation results for devices based on realistic commercial processes. It is shown that the MBGT represents a viable power semiconductor device technology, suitable for a diverse range of applications. © IEE, 1998.

Axial compressor response to inlet flow distortions by a CFD analysis

The usual approach to compressor design considers uniform inlet flow characteristics. Especially in aircraft applications, the inlet flow is quite often non uniform, and this can result in severe performance degradation. The magnitude of this phenomenon is amplified in military engines due to the complexity of inlet duct configurations and the extreme flight conditions. CFD simulation is an innovative and powerful tool for studying inlet distortions and can bring this inside the very early phases of the design process. This project attempts to study the effects of inlet flow distortions in an axial flow compressor trying to minimize the use computer resources and computational time. The first stage of a low bypass ratio compressor has been analyzed and its clean and distorted performance compared outlining the principal changes due to uneven flow distribution: drop in mass flow, increase in pressure and temperature ratios, decrease in surge margin. Three different studies have then been conducted to better understand the effects of the level, the type and the frequency of the distortion.

The effect of an upstream turbine on a low-aspect ratio vane

The interaction between a high-pressure rotor and a downstream vane is dominated by vortex-blade interaction. Each rotor blade passing period two co-rotating vortex pairs, the tip-leakage and upper passage vortex and the lower passage and trailing shed vortex, impinge on, and are cut by, the vane leading edge. In addition to the streamwise vortex the tip-leakage flow also contains a large velocity deficit. This causes the interaction of the tip-leakage flow with a downstream vane to differ from typical vortex blade interaction. This paper investigates the effect these interaction mechanisms have on a downstream vane. The test geometry considered was a low aspect ratio second stage vane located within a S-shaped diffuser with large radius change mounted downstream of a shroudless high-pressure turbine stage. Experimental measurements were conducted at engine-representative Mach and Reynolds numbers, and data was acquired using a fast-response aerodynamic probe upstream and downstream of the vane. Time-resolved numerical simulations were undertaken with and without a rotor tip gap in order to investigate the relative magnitude of the interaction mechanisms. The presence of the upstream stage is shown to significantly change the structure of the secondary flow in the vane and to cause a small drop in its performance.

The effect of work processes on the casing heat transfer of a transonic turbine

This paper considers the effect of the rotor tip on the casing heat load of a transonic axial flow turbine. The aim of the research is to understand the dominant causes of casing heat-transfer. Experimental measurements were conducted at engine-representative Mach number, Reynolds number and stage inlet to casing wall temperature ratio. Time-resolved heat-transfer coefficient and gas recovery temperature on the casing were measured using an array of heat-transfer gauges. Time-resolved static pressure on the casing wall was measured using Kulite pressure transducers. Time-resolved numerical simulations were undertaken to aid understanding of the mechanism responsible for casing heat load. The results show that between 35% and 60% axial chord the rotor tip-leakage flow is responsible for more than 50% of casing heat transfer. The effects of both gas recovery temperature and heat transfer coefficient were investigated separately and it is shown that an increased stagnation temperature in the rotor tip gap dominates casing heat-transfer. In the tip gap the stagnation temperature is shown to rise above that found at stage inlet (combustor exit) by as much as 35% of stage total temperature drop. The rise in stagnation temperature is caused by an isentropic work input to the tip-leakage fluid by the rotor. The size of this mechanism is investigated by computationally tracking fluid path-lines through the rotor tip gap to understand the unsteady work processes that occur. Copyright © 2005 by ASME.

The silicon backplane design for an LCOS polarization-insensitive phase hologram SLM

Polarization-insensitivity is achieved in a reflective spatial light modulator by laying a quarter-wave plate (QWP) at the incident wavelength directly over the mirror pixels of a silicon backplane, and forming a nematle Fréedrickcz cell over the QWP to modulate the reflected phase. To achieve the highest drive voltage from the available silicon process, a switched voltage common front electrode design is described, with variable amplitude square wave drive to the pixels to maintain constant root-mean-square drive and minimize phase fluctuations during the dc balance refresh cycle. The silicon has been fabricated and liquid-crystal-on-silicon cells both with and without the QWP assembled; applications include optically transparent switches for optical networks, beam steering for add-drop multiplexers for wavelength-division- multiplexing telecommunications, television multicast, and holographic projection.

Ink-jet printing for patterning engineering surfaces

This work explored the use of industrial drop-on-demand inkjet printing for masking steel surfaces on engineering components, followed by chemical etching, to produce patterned surfaces. A solvent-based ink was printed on to mild steel samples and the influences of substrate topography and substrate temperature were investigated. Contact angle measurements were used to assess wettability. Regular patterns of circular spots (∼60 /on diameter) and more complex mask patterns were printed. Variation of the substrate temperature had negligible effect on the final size of the printed drops or on the resolution achieved. Colored optical interference fringes were observed on the dried ink deposits and correlated with film thickness measurements by whitelight interferometry.

SOI diode temperature sensor operated at ultra high temperatures-a critical analysis

This paper investigates the performance of diode temperature sensors when operated at ultra high temperatures (above 250°C). A low leakage Silicon On Insulator (SOI) diode was designed and fabricated in a 1 μm CMOS process and suspended within a dielectric membrane for efficient thermal insulation. The diode can be used for accurate temperature monitoring in a variety of sensors such as microcalorimeters, IR detectors, or thermal flow sensors. A CMOS compatible micro-heater was integrated with the diode for local heating. It was found that the diode forward voltage exhibited a linear dependence on temperature as long as the reverse saturation current remained below the forward driving current. We have proven experimentally that the maximum temperature can be as high as 550°C. Long term continuous operation at high temperatures (400°C) showed good stability of the voltage drop. Furthermore, we carried out a detailed theoretical analysis to determine the maximum operating temperature and exlain the presence of nonlinearity factors at ultra high temperatures. © 2008 IEEE.

Compressor wake/leading-edge interactions at off design incidences

In this paper, the effects of wake/leading-edge interactions were studied at off-design conditions. Measurements were performed on the stator-blade suction surface at midspan. The leading-edge flow-field was investigated using hotwire micro-traverses, hotfilm surface shear-stress sensors and pressure micro-tappings. The trailing-edge flow-field was investigated using hotwire boundary-layer traverses. Unsteady CFD calculations were also performed to aid the interpretation of the results. At low flow coefficients, the time-averaged momentum thickness of the leading-edge boundary layer was found to rise as the flow coefficient was reduced. The time-resolved momentum-thickness rose due to the interaction of the incoming rotor wake. As the flow coefficient was reduced, the incoming wakes increased in pitch-wise extent, velocity deficit and turbulence intensity. This increased both the time-resolved rise in the momentum thickness and the turbulent spot production within the wake affected boundary-layer. Close to stall, a drop in the leading-edge momentum thickness was observed in-between wake events. This was associated with the formation of a leading-edge separation bubble in-between wake events. The wake interaction with the bubble gave rise to a shedding phenomenon, which produced large length scale disturbances in the surface shear stress. Copyright © 2008 by ASME.

Unsteady ejectors: The effect of driver jet mark-space ratio

mark Unsteady ejectors can be driven by a wide range of driver jets. These vary from pulse detonation engines, which typically have a long gap between each slug of fluid exiting the detonation tube (mark-space ratios in the range 0.1-0.2) to the exit of a pulsejet where the mean mass flow rate leads to a much shorter gap between slugs (mark-space ratios in the range 2-3). The aim of this paper is to investigate the effect of mark-space ratio on the thrust augmentation of an unsteady ejector. Experimental testing was undertaken using a driver jet with a sinusoidal exit velocity profile. The mean value, amplitude and frequency of the velocity profile could be changed allowing the length to diameter ratio of the fluid slugs L/D and the mark-space ratio (the ratio of slug length to the spacing between slugs) L/S to be varied. The setup allowed L/S of the jet to vary from 0.8 to 2.3, while the L/D ratio of the slugs could take any values between 3.5 and 7.5. This paper shows that as the mark-space ratio of the driver jet is increased the thrust augmentation drops. Across the range of mark-space ratios tested, there is shown to be a drop in thrust augmentation of 0.1. The physical cause of this reduction in thrust augmentation is shown to be a decrease in the percentage time over which the ejector entrains ambient fluid. This is the direct result ofthe space between consecutive slugs in the driver jet decreasing. The one dimensional model reported in Heffer et al. [1] is extended to include the effect of varying L/S and is shown to accurately capture the experimentally measured behavior ofthe ejector. Copyright © 2010 by the American Institute of Aeronautics and Astronautics, Inc.

The effects of corona treatment on impact and spreading of ink-jet drops on a polymeric film substrate

The effects of varying corona surface treatment on ink drop impact and spreading on a polymer substrate have been investigated. The surface energy of substrates treated with different levels of corona was determined from static contact angle measurement by the Owens and Wendt method. A drop-on-demand print-head was used to eject 38 μm diameter drops of UV-curable graphics ink travelling at 2.7 m/s on to a flat polymer substrate. The kinematic impact phase was imaged with a high speed camera at 500k frames per second, while the spreading phase was imaged at 20k frames per secoiui. The resultant images were analyzed to track the changes in the drop diameter during the different phases of drop spreading. Further experiments were carried out with white-light intetferometry to accurately measure the final diameter of drops which had been printed on different corona treated substrates and UV cured. The results are correlated to characterize the effects of corona treatment on drop impact behavior and final print quality.

Boundary-layer suction system design for laminar-flying-wing aircraft

The present study aims to provide insight into the parameters affecting practical laminar-flow-control suction power requirements for a commercial laminar-flying-wing transport aircraft. It is shown that there is a minimum power requirement independent of the suction system design, associated with the stagnation pressure loss in the boundary layer. This requirement increases with aerofoil section thickness, but depends only weakly on Mach number and (for a thick, lightly loaded laminar flying wing) lift coefficient. Deviation from the optimal suction distribution, due to a practical chamber-based architecture, is found to have very little effect on the overall suction coefficient; hence, to a good approximation, the power penalty is given by the product of the optimal suction flow rate coefficient and the average skin pressure drop. In the spanwise direction, through suitable choice of chamber depth, the pressure drop due to frictional and inertial effects may be rendered negligible. Finally, if there are fewer pumps than chambers, the average pressure drop from the aerofoil surface to the pump collector ducts, rather than to the chambers, determines the power penalty. For the representative laminar-flying-wing aircraft parameters considered here, the minimum power associated with boundary-layer losses alone contributes some 80-90% of the total power requirement. © 2011 by the American Institute of Aeronautics and Astronautics, Inc.

Simulation of solitary wave impact on coastal structures using weakly compressible and incompressible SPH methods

In this paper, we engage a Lagrangian, particle-based CFD method, named Smoothed Particle Hydrodynamic (SPH) to study the solitary wave motion and its impact on coastal structures. Two-dimensional weakly compressible and incompressible SPH models were applied to simulate wave impacting on seawall and schematic coastal house. The results confirmed the accuracy of both models for predicting the wave surface profiles. The incompressible SPH model performed better in predicting the pressure field and impact loadings on coastal structures than the weakly compressible SPH model. The results are in qualitatively agreement with experimental results. Copyright © 2011 by the International Society of Offshore and Polar Engineers (ISOPE).

Imbibition dynamics of nano-particulate ink-jet drops on micro-porous media

Ink-jet printing of nano-metallic colloidal fluids on to porous media such as coated papers has become a viable method to produce conductive tracks for low-cost, disposable printed electronic devices. However, the formation of well-defined and functional tracks on an absorbing surface is controlled by the drop imbibition dynamics in addition to the well-studied post-impact drop spreading behavior. This study represents the first investigation of the real-time imbibition of ink-jet deposited nano-Cu colloid drops on to coated paper substrates. In addition, the same ink was deposited on to a non-porous polymer surface as a control substrate. By using high-speed video imaging to capture the deposition of ink-jet drops, the time-scales of drop spreading and imbibition were quantified and compared with model predictions. The influences of the coating pore size on the bulk absorption rate and nano-Cu particle distribution have also been studied.