An investigation into the sensory application of DBD plasma actuators for pressure measurement

This paper investigates the effect of air pressure on the current used by dielectric barrier discharge (DBD) plasma actuators and the voltage limits for plasma production in these actuators. The purpose of this research was to determine whether DBD plasma actuators have potential for application as a pressure sensor at sub-atmospheric pressure conditions. It was found that these actuators were sensitive to air pressure and possessed a distinct, non-linear relationship between the electrical current consumed by them and ambient pressure. It was also found that lower and upper voltage limits for plasma production increased approximately linearly with pressure.     

Centimeter-scale high-resolution metrology of entire CVD-grown graphene sheets

A high-throughput metrology method for measuring the thickness and uniformity of entire large-area chemical vapor deposition-grown graphene sheets on arbitrary substrates is demonstrated. This method utilizes the quenching of fluorescence by graphene via resonant energy transfer to increase the visibility of graphene on a glass substrate. Fluorescence quenching is visualized by spin-coating a solution of polymer mixed with fluorescent dye onto the graphene then viewing the sample under a fluorescence microscope. A large-area fluorescence montage image of the dyed graphene sample is collected and processed to identify the graphene and indicate the graphene layer thickness throughout the entire graphene sample. Using this metrology method, the effect of different transfer techniques on the quality of the graphene sheet is studied. It is shown that small-area characterization is insufficient to truly evaluate the effect of the transfer technique on the graphene sample. The results indicate that introducing a drop of acetone or liquid poly(methyl methacrylate) (PMMA) on top of the transfer PMMA layer before soaking the graphene sample in acetone improves the quality of the graphene dramatically over immediately soaking the graphene in acetone. This work introduces a new method for graphene quantification that can quickly and easily identify graphene layers in a large area on arbitrary substrates. This metrology technique is well suited for many industrial applications due to its repeatability and flexibility.     

Effect of flow conditions on spray cone angle of a two-fluid atomizer

A visual study is conducted to determine the effects of operating conditions on the spray cone angle of a two-fluid atomizer. The liquid (water) jets exit from peripheral inclined orifices and are introduced into a high-speed gas (air) stream in the gravitational direction. Using a high-speed imaging system, the spray cone angle is determined for Reynolds numbers ranging from 4×10⁴ to 9×10⁴ and different Weber numbers up to 140. The droplet sizes (Sauter mean diameter) and their distributions are determined using a Malvern Mastersizer X. The results show that the spray cone angle depends on the operating conditions, especially in lower values of Reynolds and Weber numbers. An empirical correlation is also obtained to predict the spray cone angle in terms of these two parameters.     

A pseudo-lucky electron model for simulation of electron gatecurrent in submicron NMOSFET's

An energy parameterized pseudo-lucky electron model for simulation of gate current in submicron MOSFET's is presented in this paper. The model uses hydrodynamic equations to describe more correctly the carrier energy dependence of the gate injection phenomenon. The proposed model is based on the exponential form of the conventional lucky electron gate current model. Unlike the conventional lucky electron model, which is based on the local electric fields in the device, the proposed model accounts for nonlocal effects resulting from the large variations in the electric field in submicron MOSFET's. This is achieved by formulating the lucky electron model in terms of an effective-electric field that is obtained by using the computed average carrier energy in the device and the energy versus field relation obtained from uniform-field Monte Carlo simulations. Good agreement with gate currents over a wide range of bias conditions for three sets of devices is demonstrated     

MOSFET drain engineering analysis for deep-submicrometerdimensions: a new structural approach

A new MOS transistor structural approach (hot-carrier-induced MOSFET) capable of substantially suppressing adverse hot-carrier effects, while maintaining the other desired performance and manufacturability characteristics of deep-submicrometer MOSFETs (L _gate⩽0.35 μm) is described. This structure is unique in having a lower doped N^- region located behind (or above) a very shallow, steeply profiled source/drain junction. In contrast, LDD types of MOSFETs have an N^- region with a more graded doping profile immediately adjacent to the channel region. The simulated characteristics of the HCS MOSFET structure indicate approximately one order of magnitude less substrate current in comparison to an LDD type of MOSFET whose structure and doping parameters are optimized for combined performance, reliability, and manufacturability. In terms of combined performance, reliability, and manufacturability, the HCS MOSFET should permit MOSFET devices to be more successfully scaled at deep-submicrometer dimensions     

Combined experimental and numerical analysis of bulge test at high strain rates using split Hopkinson pressure bar apparatus

High strain rate bulge test technique which is introduced in this paper adopts a rubber-pad as pressure carrying medium to bulge a sheet metal at high velocity using split Hopkinson pressure bar (SHPB) system. The experimental set-up is based on conventional hydraulic bulge test which is modified to mount on SHPB. The thickness thinning of the sheet metal during the test will be considered as a measure of true strain of the bulged sheet. The theoretical approach is developed in this study to attain pressure–strain curves of sheet metals during high strain rate bulge forming process. This approach is followed by a finite element simulation of the process in ABAQUS/Explicit software. To verify the developed method, analytical and finite element methods are compared with experiments.     

Modelling of kinetic friction in V-bending of ultra-high-strength steel sheets

The Stribeck friction model was investigated in this study to predict springback of high-strength steel sheets. The coefficient of friction in Stribeck curve depends on sliding velocity and contact pressure. The plane-strain bending process is simulated in ABAQUS/Standard. The influence of forming speed, over-pressing and holding time on springback behaviour of sheets was studied numerically. By plotting the variation of bending angle with punch stroke, we found that the loading curve of finite element analysis showed similar results to the experiments. The unloading curves of FE analysis with friction models based on Stribeck curve and Coulomb law showed good agreement with experiments with error less than 1.5%. Forming speed of up to 50 mm/s does not have significant effect on springback. The effect of holding time on reducing springback is small, but over-press has large effect on reducing springback. The results showed that Stribeck model is suitable for sheet metal forming simulations, especially at higher forming speeds and pressures.     

A friction model for dry contacts during metal-forming processes

In a metal-working process, the friction between the material and the tools influences the process by modifying the strain distribution of the workpiece. This frictional behavior is often taken into account by using a constant coefficient of friction in the finite element simulations. However, friction coefficient varies in time and space with many parameters. This paper aims at modeling of friction in dry contacts which happens at metal-forming processes in the lack of lubricant. The coefficient of dry friction in this model is a function of contact area ratio (which is a function of surface contact characteristics) and strain hardening exponent (material property). The V-bending process of aluminum alloy 6061-T4 sheets was studied experimentally and numerically using ABAQUS/Standard with two kinds of friction models: Coulomb friction and newly developed dry friction models. The results clearly showed that the developed dry friction model has better results in predicting load-stroke curves and springback compared to traditional Coulomb friction model. The FE prediction error for 6061-T4 AA is 16.9% using Coulomb friction model and 9.2% using dry friction model.