High Aspect Ratio Design Research Articles

FCS technology: A novel electrodynamic transducer architecture

For a century now, acoustic electrodynamic transducers have been bound by axisymmetric motor structures for high performance due to the assumption in transducer theory that the diaphragm moves pistonically for all operating frequencies. This is of course a flawed assumption, and results in much research and development being focused on the vibro-acoustic components of the driver to minimize cone breakup at higher frequencies.A new architecture for the electrodynamic motor has been developed which helps to address this inherent problem. Flat Core Speaker (FCS) technology presents an architecture that is a rearrangement of the conventional electrodynamic motor structure with a planar voice coil and bobbin assembly that is situated between two parallel bar magnets. This results in a high aspect ratio design where the bobbin runs along the length of a flat diaphragm, leading to even force distribution, and therefore pistonic movement, while utilizing a thin profile with a flat diaphragm. COMSOL simulations and Klippel measurement data support these claims and show evidence of FCS technology having comparable performance to conventional drivers in a slimmer profile and blowing conventional high aspect ratio driver performance out of the water.

A videogrammetric system for measuring the full-field blade deformation of a heavy-duty helicopter's rotating rotor.

In this paper, a videogrammetric system, based on three-dimensional digital image processing and industrial close range photogrammetry technology, is proposed to solve the three-dimensional motion and deformation parameters of a rotating blade by identifying a speckle pattern. For the high aspect ratio and flexible rotor blade design often used in heavy-duty helicopters, there are extremely complex aerodynamic, dynamic, and coupling problems that require solutions to measure the full-field deformation of the rotating blade in the test condition of a rotor test tower. The key issues involved include a two-step calibration method using separate internal and external parameters for a large field of view, and a reliable estimation of the seed point method for a large deformation and weak correlation speckle images match. The system was developed and a simulation test was conducted on a rotor test tower. The results show that the proposed system is practicable to measure the surface displacement and motion parameters of a high-speed rotating rotor blade.

Design of SFR fluidic diode axial port using topology optimization

Abstract A fluidic diode is a passive component that direct natural circulation during Loss of Forced Convection (LOFC) in the hybrid-type SFRs. In order to enhance the performance (diodicity) of the existing vortex-type fluidic diode (FD) design, topology optimization, a mathematical method to optimize material distribution in a design domain, is applied to the axial port. In this paper, the topology optimization is conducted for a 2-D axisymmetric domain and two designs with different aspect ratios are finally selected. In this process, design simplification and modification are also conducted based on sensitivity study. Performance of the final optimized designs are validated using detailed 3-D CFD analysis for various parameters, such as Reynolds numbers, entrance lengths, and turbulence models. It is found that the diodicity of the optimized axial port ranges from 1.7 to 2.3 for the low aspect-ratio design (design A) and from 3.7 to 4.5 for the high aspect-ratio design (design B). Friction loss coefficients for the final designs are evaluated for both forward and backward flows using the CFD analysis.

Toward Handheld Diagnostics of Cancer Biomarkers in Breath: Micro Preconcentration of Trace Levels of Volatiles in Human Breath

This paper introduces, for the first time, Maltese-cross pillar design implemented in a 7 mm × 7 mm × 0.35 mm cavity for high-performance microfabricated preconcentrators (μPCs). This high-aspect ratio design provides more surface area over the previously reported basic geometric shapes. Results showed that Maltese-cross provided a 27% increase in performance. Moreover, reducing the pillar spacing from 100 μm to 10 μm and arranging the pillars in staggered fashion have resulted in 145% and 85% increase in performance, respectively. Therefore, it was concluded that both surface area and flow pattern contribute significantly to the device performance. These μPCs achieved high adsorption capacity making them suitable for handheld breath analyzers to concentrate and identify trace-level (low ppb) volatile compounds (cancer biomarkers) found in human breath.

A low aspect ratio electrothermal gun for metal plasma vapor discharge and ceramic nanopowder production

Traditionally, the electrothermal gun design has the bore of a large aspect ratio; however, a low aspect ratio design with a shorter bore length has been employed for efficient production of metal plasma vapors and synthesis of nanomaterials. In a comparison of the arc resistance-current relationship, a low aspect ratio design is found to exhibit distinctively different characteristics compared to a high aspect ratio design, and this trend is explained by the scaling law of plasma properties including theory of plasma electrical conductivity. A one-dimensional isothermal model has been applied to the present experiments to confirm the scaling laws, and it was found that the present modification of the electrothermal gun is able to produce fully ionized metal plasma vapor, while the plasma vapor produced in a conventional design is partially ionized. Also, by reacting metal plasma vapors with the controlled gases in the reaction chamber, nanoscale materials such as aluminum oxide, aluminum nitride, and titanium oxide were synthesized successfully.

An Evaluation of an Autothermal Aerobic Digestion System

The specifications of the Safe Sludge Matrix mean that there is a need to examine treatment processes which achieve a degree of digestion. There are a number of processes which operate in the thermophilic range. This study examines one such option, an autothermal thermophilic aerobic digester (ATAD) which uses a high aspect ratio design and a hyperbolic stirrer. Mixing times were found to range from 4 to 10 minutes and oxygenation capacities from 10 to 30 kg h −1 . Using a hydraulic retention time of 7 days, autothermal conditions did occur with a specific heat yield of 15.68 MJ kg −1 oxygen. A comparison of a range of air:liquid ratios (v/v) showed that a ratio of 0.5:1 would be recommended. This gave a reduction in volatile solids of 35%.

Damascene test structures for the evaluation of barrier layer performance against copper diffusion

Both IMP TaN and CVD TiN barriers have been shown to be excellent materials against copper diffusion using etch-pit, bias-thermal-stress (BTS) or C(V) tests on planar structures. These results however cannot account for the real barrier thickness and stoichiometry when deposited in damascene features. Such information is critical for advanced technologies exploiting high aspect ratio design rules. Via structures, 0.32 and 0.26 μm in diameter and 1 μm deep, etched through SiO 2 down to bare silicon, are combined with a standard etch-pit test to look for the formation of copper silicide as a function of barrier material and process conditions. Using these test-structures it was shown that the CVD process would be mandatory to maintain the required copper barrier performance in sub-quarter micron technology.

MHD Stability Considerations for the High Aspect Ratio Design

Global MHD stability calculations using the PEST code have been carried out as part of the US ITER team’s High Aspect Ratio Design (HARD) study. Approximately 15,000 cases have been evaluated both for global and local (ballooning) modes. In addition to aspect ratio variations [2.78 < A < 5], a range of shapes (1.4 < κ < 2.0, 0. < δ < 0.6) has been examined and the safety factor has been varied: q(0) was varied from 1.05 to 1.85 and qψ from 3.1 to 4.55. For global aspect ratio scaling, these results show no significant increase or decrease in the maximum Troyon parameter, within the level of variation imposed by profile differences: the scaling of the maximum Troyon parameter (g) is found to be independent of A, if optimal values are considered at each aspect ratio. Specific results for the HARD configuration (A = 4.0, κ = 2.0, δ = 0.4 and q = 3.1, 4) show that the grequired can be obtained with values of 1i(3) = 0.65 - 0.85 in both the ignition and steady state phases.

DC and microwave characteristics of sub-0.1- mu m gate-length planar-doped pseudomorphic HEMTs

Analytical modeling of these very-short-channel HEMTs (high-electron-mobility transistors) using the charge-control model is given. The calculations performed using this model indicate a very high electron velocity in the device channel (3.2+or-0.2*10/sup 7/ cm/s) and clearly demonstrate the advantages of the planar-doped devices as compared to the conventional uniformly doped HEMTs. Devices with different air-bridged geometries have been fabricated to study the effect of the gate resistance on the sub-0.1- mu m HEMT performance. With reduced gate resistance in the air-bridge-drain device, noise figures as low as 0.7 and 1.9 dB were measured at 18 and 60 GHz, respectively. Maximum available gains as high as 13.0 dB at 60 GHz and 9.2 dB at 92 GHz, corresponding to an f/sub max/ of 270 GHz, have also been measured in the device. Using the planar-doped pseudomorphic structure with a high gate aspect-ratio design, a noise figure of less than 2.0 dB at 94 GHz is projected based on expected further reduction in the parasitic gate and source resistances.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Millimeter-wave performance of ultrasubmicrometer-gate field-effect transistors: A comparison of MODFET, MESFET, and PBT structures

Device structures for the modulation-doped high-electron-mobility transistor (MODFET or HEMT), the metal Schottky-barrier gate transistor (MESFET), and the permeable-base transistor (PBT) With 0.1- to 0.25-µm gate lengths have been examined for their millimeter-wave performance. In particular, their unity-current-gain frequency (f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</inf> ), maximum oscillation frequency (f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</inf> ), and the stability of power gains are Compared. It is shown that in field-effect transistors with gate lengths below 0.25 µm, the high aspect ratio design approach, involving the ratio of the gate length to its associated depletion depth, needs to be extended to include the gate-to-drain separation in an effective gate-length concept. Using the charge-control approach in conjunction with the carrier velocity saturation effect, it is shown that the overall transit time delay across the total effective gate length results in an effective gate capacitance that is significantly larger than that due to the physical size of the gate itself. It is shown with specific examples that a successful design of these ultrasubmicrometer gate structures depends on the choice of the gate-to-drain separation (L <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">GD</inf> ) and the separation (d <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</inf> ) between the gate and the channel sheet Charge, with an appropriate choice of doping concentration consistent with the desired drain voltage operation. The designs have been based on practically obtainable values of the gate and source series resistances. When the actual gate length is much smaller than L <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">GD</inf> , as in the case of PBT's, it is shown that the stable power gain margin in these devices is determined by the square of the aspect ratio (L <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">GD</inf> /d <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</inf> ). The results show that an f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</inf> of approximately 350 GHz can be achieved from a MODFET structure with an effective gate length of 0.14 µm. In a PBT structure an f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</inf> exceeding 500 GHz can be achieved with an effective gate length of 0.15 µm, and in a similar MESFET structure an f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</inf> of approximately 450 GHz can be achieved. The device design approach presented clearly indicates the possibility of achieving FET'S operating beyond 200 GHz with useful power gains.

A high aspect ratio design approach to millimeter-wave HEMT structures

In MESFET and HEMT structures as the gate length is reduced below 0.5 µm in an attempt to achieve amplification at highest possible frequencies, it is essential that the depletion depth under the gate be also reduced in order to preserve a high aspect ratio that ensures a high device voltage gain factor (g <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</inf> /g <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> ) and a reasonable value of stable power gain at high frequencies. Results based on this design approach indicate that an n-A1GaAs/GaAs HEMT structure with 0.25-µm gate length could provide stable power gain in excess of 6 dB at the unity current gain frequency of 92.4 GHz, and for an aspect ratio of ten it is difficult to reduce the gate length below 0.25 µm.