Micromachined acoustic-wave liquid ejector

This paper describes the design and performance of micromachined, self-focusing acoustic-wave liquid ejector (AWLE) that requires no heat, nozzle, nor acoustic lens. The AWLE has a very simple device structure and is easy to fabricate. Three versions of AWLE have been designed, fabricated, and tested for an ink-jet printing application. Also developed are computer simulation and design aids that take into account the acoustic loss in water and the two-time wave reflections at the water-air and water-transducer interfaces. The AWLE has been observed to eject water droplets of about 5 μm in diameter with radio frequency (RF) pulses of 5 μs pulsewidth. Overall, the AWLE has been shown to be capable of improving the printing resolution and speed of ink-jet printing significantly     

Large processors are good in VLSI chips

We show that any circuit modeled by an N-node graph of O(N^α) separator (α > $\text{1}\text{2}$) can be laid out in O(N^2α) area, even if each processing element occupies O(N^2α-1) area. When α = $\text{1}\text{2}$, with each processing element being O(log²N) area, it can still be laid out in O(N log²N) area.     

Temporal analysis of power law liquid jets

In this paper we investigate the breakup mechanisms of power law liquid jets. The viscosity of the liquid is represented the Carreau-Yasuda model, and the surface tension of the liquid jet has a variation (gradient) along the jet axial direction. The surface tension gradient may be introduced by the thermal disturbance of the jet surface as it comes of out an orifice. The Carreau-Yasuda fluid has a power law viscosity bounded by two plateaus, the higher plateau at zero strain rate, μ₀, and the lower plateau at the infinite strain rate, μ_∞. The governing equation for the surface profile of the liquid jet is derived in the forms of a partial differential equation (PDE), as well as an ordinary differential equation (ODE). The PDE and ODE are solved for various cases of Carreau-Yasuda fluid to study the effect of fluid properties on jet breakup. The effects of various parameters on the instability behavior are studied in comparison with two Newtonian jets with upper and lower bound viscosities, μ₀ and μ_∞. A number of quantitative conclusions and sensitivities on the instability behavior of non-Newtonian jets are investigated. It is found that the jet breakup mechanism depends on the properties of the fluid as well as the wave number of the thermal disturbance that causes the surface tension gradient. In contrast to the Newtonian liquid where the jet surface profile has the same frequency as the surface tension gradient, the nonlinear nature of the Carreau-Yasuda constitutive behavior may enable the jet surface profile at frequencies higher than that of the surface tension gradient. This leads to significant surface profile oscillation within one wavelength of the surface tension gradient and the generation of small satellite drops. It is worth noting that at a small wave number the breakup time for the Carreau-Yasuda fluid maybe shorter than that of the Newtonian jet with μ_∞, although the Newtonian jet has a lower viscosity.     

Computing motion using analog VLSI vision chips: An experimental comparison among different approaches

We have designed, built and tested a number of analog CMOS VLSI circuits for computing 1-D motion from the time-varying intensity values provided by an array of on-chip phototransistors. We present experimental data for two such circuits and discuss their relative performance. One circuit approximates the correlation model while a second chip uses resistive grids to compute zero-crossings to be tracked over time by a separate digital processor. Both circuits integrate image acquisition with image processing functions and compute velocity in real time. For comparison, we also describe the performance of a simple motion algorithm using off-the-shelf digital components. We conclude that analog circuits implementing various correlation-like motion algorithms are more robust than our previous analog circuits implementing gradient-like motion algorithms.     

硅微机械陀螺的接口检测技术

研究了微陀螺的电容变化率为１０－７～１０－８时的微弱输出信号的检测技术,这是微机械器件研制中具有普遍性的技术难点。在研究检测微小电容变化量的积分电路的基础上,进一步采用了可抑制低频噪声和漂移的相关双采样技术,以及抑制由开关的电荷注入引起的误差的技术。     

Design process for developing a liquid cooling garment hood

A liquid cooling garment (LCG) protects astronauts by providing cooling effects and preventing them from overheating. The objectives of this project were to improve fit and comfort of the original LCG hood of the MACS-Delphi garment and develop a new prototype. The project was conducted by researchers with different backgrounds: apparel design and physiology and psychology. A design process framework developed by LaBat and Sokolowski (1999 LaBat, K. L. and Sokolowski, S. L. 1999. A three-stage design process applied to an industry-university textile product design project. International Textile & Apparel Association to Clothing and Textiles Research Journal, 17: 11–20. [Crossref] , [Google Scholar]) was used in order to help facilitate the process and aid in communication during the multi-disciplinary collaboration. Four crucial problems were identified: 1) the tubing layout that circulates water did not conform to the shape of the head and tubing distribution was not maximised; 2) a difficult stitching method was being used to attach tubing; 3) fabric sources were inconsistent; 4) the hood did not fit properly. Each problem was addressed, improvements implemented and a revised hood was developed. The hood was tested in an environmental chamber and demonstrated effective cooling. Revisions implemented for the LCG hood may be applied to revisions of the whole-body LCG.

Statement of Relevance:The objectives of this project were to improve fit and comfort of the original LCG hood and develop a new prototype. The new prototype will increase safety of the astronauts by providing better heat extraction quality and improved fit and increased wearer comfort.     

Micromachined electrodes for biopotential measurements

We describe the microfabrication, packaging and testing of a micromachined dry biopotential electrode, (i.e., where electrolytic gel is not required). It consists of an array of micro-dimensioned, very sharp spikes, (i.e., needles) designed for penetration of human skin which circumvent high impedance problems associated with layers of the outer skin. The spikes are etched in silicon by deep reactive ion etching and are subsequently covered with a silver-silverchloride (Ag-AgCl) double layer. The electrode-skin-electrode impedance of dry spiked electrodes having a size of 4×4 mm² is reduced compared to standard electrodes using electrolytic gel and having a comparable size. Recorded low amplitude biopotentials resulting from the activity of the brain, (i.e., EEG signals) are of high quality, even for spiked electrodes as small as 2×2 mm². The spiked electrode offers a promising alternative to standard electrodes in biomedical applications and is of interest in research of new biomedical methods     

Multi-loop control of liquid cooling garment systems

In this study the effects of multi-loop control of liquid cooling garments (LCGs) under exercise heat stress conditions were investigated by experiments and theoretical analysis. A triple-loop LCG, by which the torso, arms and legs could be independently cooled, was used in the two series of experiments carried out in a hot environment (35 degrees C/40% RH). The experiment consisted of rest, exercise on an ergometer at 70 W and exercise at 110 W. In the first experiment, each water inlet temperature (TWI) was adjusted according to the local thermal sensation. In the second experiment, TWI for the torso including arms and TWI for the legs were regulated by a skin temperature controller with set-point adjustment via heart rate. The experiments showed that a multi-loop LCG is more effective than a single-loop LCG in providing thermal sensation and comfort adjusted to the requirements of the different parts of the body, and that a skin temperature controller could be applied to a multi-loop system. The theoretical analysis was carried out using a mathematical model of thermoregulation. The results showed that a strong cooling of the surface over the working muscles (legs) provided the greatest thermoregulatory advantage during low body exercise, because most of the heat generated within the working muscles can be removed directly by heat conduction to the skin. Optimization of a human/LCG system could be attained by an optimal configuration and control. However, an optimal configuration always depends on the application purpose of an LCG system.     

Micromachined gas sensors for environmental pollutants

An Au doped tin oxide thin film was deposited as base material for carbon monoxide detection over a micromachined substrate. The performances of a recent technique to heat the device, named fast pulsed temperature supply, are presented. This technique exploits the property that, due to the very low thermal mass of the membrane, the term required to reach steady state conditions is very short (about 40 ms). The sensor heater is periodically supplied for very short terms, hundred of milliseconds, and kept off for long ones, seconds or more. Besides a strong reduction of power consumption compared with isothermal characterization, an increase of sensitivity is observed. Different shapes of the heating wave were examined and results are summarized and compared. Received: 1 June 1999 / Accepted: 2 June 1999     

On the density and discrepancy of a 2D point set with applications to thermal analysis of VLSI chips

In this era of giga-scale integration, thermal analysis has become one of the hot topics in VLSI chip design. Active thermal sources may be abstracted as a set of weighted points on a 2D chip-floor. The conventional notion of discrepancy that deals with the congestion properties of a set of scattered points may not be able to capture properly all real-life instances in this context. In this paper, we have introduced a new concept, called the density of a region to study some of the properties of the distribution of these weighted points. We prove several counter-intuitive results concerning the properties of the regions that have maximum or minimum density. We then outline algorithms for recognizing these regions. We also compare the attributes of density with the existing concept of discrepancy.     

Micromachined infrared pneumatic detector for gas sensor

We present a micromachined IR detector based on the principle of a pneumatic cell and suited as an IR detector in a miniaturised gas sensor. The detector basically consists of a sealed cavity, in which the heat generated by absorbed IR light results in an increased gas pressure. This pressure rise is detected capacitively. The theoretical performance of a 1 mm² micromachined device is calculated, and it is shown that a detectivity of 3.6·10⁹ cm. Hz^1/2/W can be expected. Moreover, a pneumatic gas leak is proposed to avoid thermal drift. Using conventional Silicon micromachining techniques, a prototype was fabricated which confirmed the principle of operation., The experimental results are compared to the theory.     

Numerical investigations in Rayleigh breakup of round liquid jets with VOF methods

Simulations of the growth of a capillary instability and of the breakup of a jet were carried out using a one-fluid model to describe the two-phase flow motion and a VOF approach to capture the interface. The model considered each phase as fictitious sub-domains and accounted implicitly for jump conditions at the interface through a unique set of equations for which a source term of surface tensions appeared in momentum equations. The predominance of capillary effects in the breakup mechanism required to accurately describe the surface tension contribution. The Brackbill surface model was chosen because of its simplicity to represent tension forces, although it was known to generate parasitic currents susceptible to limit its precision. The flow incompressibility was ensured with an augmented Lagrangian method in case of sequential calculations and by a predictor/corrector approach for 3D simulations that required parallel computations. As a first step, the numerical methods were validated by simulating the growth of a capillary instability and comparing results to those predicted by the Rayleigh theory for capillary instabilities. The consistency of the Brackbill surface tension model and the accuracy of the methods were evaluated via a convergence study. As a second step, the simulation of a jet breakup was carried out using water as injected liquid and compressed carbon dioxide as surrounding medium. It was shown that the simulation predicted accurately the breakup length and the droplet size evidenced experimentally in literature.     

Micromachined thermal shear-stress sensor for underwater applications

This paper reports the development of micromachined thermal shear-stress sensors for underwater applications. The thermal shear-stress sensor is a polysilicon resistor sitting atop a vacuum-insulated nitride diaphragm. Special challenges for underwater measurements, such as the waterproof coating and minimization of pressure crosstalk, have been addressed. More rigid diaphragms than the aerial sensors are implemented to increase the operating range and reduce pressure crosstalk, with the cost of larger power consumption and lower sensitivity. Sensors with different diaphragm dimensions and resistor lengths have been fabricated and tested. Nearly zero pressure sensitivity has been achieved by either reducing the diaphragm width or adjusting the sensing element length. The effects of overheat ratio and operating mode on the sensor's pressure crosstalk have been discussed. Parylene C is chosen as the waterproof material for the underwater shear-stress sensors. The primary failure mode is identified as the corrosion of the soldering pads.     

A Micromachined Quartz Resonator Array for Biosensing Applications

An 8-pixel micromachined quartz crystal resonator array with a fundamental resonance frequency of 66 MHz has been designed, fabricated, and tested. A compact impedance-spectrum-analyzer electronic interface has been developed and combined with the quartz resonator array to form the biosensing system. The sensor array was calibrated using water–glycerol solutions, and the performance was found to be exactly as expected. Measurement of the crosstalk between the sensor pixels showed an isolation of $sim$ 30 dB. Selective functionalization of the pixels was achieved through the use of aqueous 3, 3 $^{prime}$-Dithiobis (sulfosuccinimidylpropionate) (DTSSP) molecules. The adsorption of avidin on DTSSP gave a frequency signal of 60 kHz in comparison to unfunctionalized pixels. The specific adsorption of avidin on functionalized pixels was confirmed through fluorescence microscopy. Comparing the performance of the micromachined quartz crystal microbalance (QCM) with a commercial 5-MHz device, we found that the micromachined QCM has a 4.25 times higher signal-to-noise ratio. Based on the measurement of the noise and using three times the frequency noise as the limit for the detection of avidin molecules, we expect to resolve a minimum of $sim$1/960 of a monolayer of avidin corresponding to an aerial mass density resolution of 0.7 $hbox{ng/cm}^{2}$ .$hfill$[2008-0196]      

A VLSI Support for GKS

This microprogrammed VLSI design places the GKS output functions on a single chip, leading the way to substantial enhancements in system performance.