Thermal ink jet technology

Micromachining and microelectromechanical system (MEMS) technology have enabled the unprecedented cost/performance ratio of thermal ink jet (TIJ) products that currently dominate the desktop color printing market. The generic TIJ operating principles are based on an intimate blend of thermodynamics, fluid dynamics, and large-scale integration (LSI) electronics. This article introduces the generic operating principles and design issues of TIJs, and the fabrication of TIJ printheads is illustrated with an implementation by the Xerox Corporation     

Life prediction of LED-based recess downlight cooled by synthetic jet

This paper details the adaptation and implementation of a proposed hierarchical model to the reliability assessment of LED-based luminaires. An Edison base ? 6 in., compatible can, downlight ? LED replacement bulb, cooled by active synthetic jets, is used as the test vehicle. Based on the identified degradation mechanisms and the experimentally obtained degradation rate of the cooling device, the reduction in the heat sink enhancement factor, and thus the increase in the LED junction temperature, is determined as a function of time. The degradation mechanisms of the dual-function power electronics – providing constant power to the LEDs and to the drivers of a series of synthetic jets – are also analyzed and serve as the basis for a hybrid model which combines these two effects on the luminaire lifetime. The lifetime of a prototypical luminaire is predicted from LED lifetime data using the degradation analyses of the synthetic jet and power electronics.     

Thermal management of AlGaN-GaN HFETs on sapphire using flip-chip bonding with epoxy underfill

Self-heating imposes the major limitation on the output power of GaN-based HFETs on sapphire or SiC. SiC substrates allow for a simple device thermal management scheme; however, they are about a factor 20-100 higher in cost than sapphire. Sapphire substrates of diameters exceeding 4 in are easily available but the heat removal through the substrate is inefficient due to its low thermal conductivity. The authors demonstrate that the thermal impedance of GaN based HFETs over sapphire substrates can be significantly reduced by implementing flip-chip bonding with thermal conductive epoxy underfill. They also show that in sapphire-based flip-chip mounted devices the heat spread from the active region under the gate along the GaN buffer and the substrate is the key contributor to the overall thermal impedance.     

Thermal ink jet dynamics: modeling, simulation, and testing

In this paper, we present a cinematographic measuring technique for visualization and characterization of dynamics in micro electro mechanical systems for the example of a thermal ink jet printhead. Furthermore, we derive a model for identification and simulation of dynamic phenomena in the thermal pneumatic microactuator of a thermal ink jet. Using this model we calculate the pressure propagation in the bubble by identifying the mathematical model with position measurements extracted from cinematographic image sequences which have been taken with our visualization equipment. The identification of the model was performed with minimizing the sum of quadratic deviations between simulated and measured values. Parameter studies with the identified model predict the behavior of the microactuator at outer pressures higher than 1 bar.     

Thermal management for multifunctional structures

Multifunctional structures (MFS) are an innovative concept that offer a new methodology for spacecraft design, eliminating chassis, cables and connectors, and integrating the electronics into the walls of the spacecraft. The MFS design consists of multilayer flexible circuit patches bonded onto a structural composite panel, and multichip modules (MCMs) performing specific functions are bonded onto the circuit patches which are interconnected via flexible circuit jumpers. Incorporation of the high power density two-dimensional (2-D) and three-dimensional (3-D) MCM's into smaller and more efficient packaging designs still has the fundamental requirement to maintain component temperatures within design limits. Higher component qualification temperatures, such as 393 K, can result in smaller spacecraft radiator areas that are consistent with efficient packaging schemes. During the MFS development effort, a structural radiator panel was fabricated using high thermal conductivity (Hi-K) composite facesheets, and several thermal management designs using combinations of Hi-K doublers (150-1500 W/m-K), Hi-K (150-700 W/m-K) corefill, and deployable radiators to maximize MCM's heat rejection. Results of the thermal vacuum tests and details of the thermal design methodology are presented in this paper     

Thermal management in semiconductor device packaging

Thermal management at device level packaging involves efficient and cost-effective removal of dissipated thermal energy from the device to assure its reliable performance over the long term. In the context of very high levels of integration of future ICs, thermal management will mean making such devices possible close to the natural limits set by thermal physics. This paper will present trends in important parameters and discuss solutions through examples.     

Denoising jet engine gas path measurements using nonlinear filters

Traditionally, linear filters have been used to smooth time series of gas path measurements before performing fault detection and isolation. However, linear filters can smooth out sharp trend shifts in the signal and are also not good at removing outliers. Since most fault detection and isolation algorithms are optimized for Gaussian noise, they can show performance degradation when outliers are present. In this study, numerical results with simulated data for engine deterioration and abrupt fault show that the nonlinear rational filter with median preprocessor are useful for gas turbine health monitoring applications resulting in noise reduction of 73%-96% while preserving signal features and removing outliers.     

Ceramic synthetic substrates using solid freeform fabrication

Three-dimensional (3-D) printing techniques were used to create lost molds for advanced inhomogeneous materials made of ceramics. The utility of this process is the ability to manipulate low-loss materials, such as alumina illustrated here, into precise, fine features as periodic macroscopic inclusions in a larger host material or air. Three periodic structures were formed using solid freeform (SFF) fabrication techniques; a two-dimensional (2-D) all-dielectric electromagnetic bandgap (EBG) substrate, a 2-D metallo-dielectric substrate filter, and a 3-D woodpile EBG structure. The design of these structures is discussed and the fabricational steps are presented in detail. This process has been utilized to develop a simple two-pole filter embedded in a substrate at 10 GHz, a single resonator at 30 GHz, and a 3-D bandgap structure from 88 to 115 GHz. The wide range of features and structures that can be accurately fabricated are highlighted.     

LED照明灯的发展概况

自高亮度白光LED问世后,由于它具有发光效率高节电效果好,并且无污染、寿命长的特点,在照明应用上受到各国的重视.用白光LED作照明灯来取代传统照明灯的研发工作不断地进行着,取得了一些成果.     

Thermal management for high-power active amplifier arrays

Much of the active array work reported to date has been directed toward the demonstration of prototypes at low-power levels. Analysis results presented here show that overheating failures will occur as these arrays are scaled to reasonable output powers. Large air-cooled heat sinks attached to the backside of a thinned array can be used for single-sided designs such as oscillator arrays, but heat sinking becomes substantially more difficult for two-sided transmission-type arrays. For these designs, a possible solution is described which uses an aluminum-nitride dielectric layer to facilitate conduction to heat sinks on the array's perimeter     

电源管理系统的散热问题及解决办法

设计一款功率转换器并不简单,因为其中涉及多方面的技术知识。出色的功率转换器设计工程师必须对模拟及混合信号电路的设计、变压器绕组、电磁兼容性、封装及散热设计有一定的认识。由于电子产品的功率密度越来越大,加上不同的电源供应系统设计各有优缺点,因此工程师必须审慎考量,作出最适当的取舍,才可确保所采用的封装及散热设计能够满足电源管理系统的要求。部分电子产品需要传送大量数据,令系统结构越趋复杂,因此散热系统的设计越来越受到高度的关注。面对这种发展趋势,     

Study of solder jet bumping process using high-speed digital camera

With the development of solder jet technology in the electronic packaging industry, the bumping process of a molten metal droplet, which determines the shape of the solder bump and is crucial for the performance of the device, has attracted great interests. The solder bumping process of a single molten micro-droplet by a solder jet was recorded using a high-speed digital camera with a frame rate of 100,000 frames per second. It was found that the surface ripples on the solder bump was caused by the interaction of the fluid flow and the heat transfer/solidification processes in the bumping process of a micro-droplet. A droplet was observed to rebound on a copper pad coated with a layer of organic solderability preservatives, which was suspected to decrease the interfacial heat transfer coefficient between the droplet and the pad lower than a minimal value, 4.07×10⁴ W/m² K, making the recoiling droplet rebound away.     

Enhancement of air jet impingement heat transfer using pin-fin heatsinks

The enhancement of heat transfer from a discrete heat source in confined air jet impingement was experimentally investigated. A variety of pin-fin heat sinks were mounted on the heat source and the resulting enhancement studied, Average heat transfer coefficients are presented for a range of jet Reynolds numbers (8000⩽Re⩽45000) and orifice diameters (12.7⩽d⩽38.1 mm). A total fin effectiveness was computed for the pinned heat sinks relative to the unpinned ones, and was in the range of 2.4 to 9.2; the highest value was obtained for the largest nozzle diameter. Heat transfer rates from the bare heat source were increased by a factor of 7.5 to 72 due to the introduction of the heat sinks. Results for the average heat transfer coefficient were correlated in terms of Reynolds number, fluid properties and geometric parameters of the heat sinks     

Drop formation characteristics of electrostatic ink jet using water-based ink

Drop formation characteristics of electrostatic ink jets using water-based ink are reported. At first, to understand drop formation phenomena and processes, we took high-speed photographs. We investigated, using one capillary and kind of ink, ink-drop frequency versus ink-flow characteristics. From these characteristics, we calculated ink-drop diameters treating a drop as a sphere. Then, from these ink-drop frequency versus ink-drop diameter characteristics, we estimated attainable ink-drop frequencies and ink-drop diameters for a specific capillary. Lastly, comparisons were made among ink-drop frequency versus recorded-diameter characteristics for different capillaries, particularly their outside diameters.     

Supersonic jet epitaxy of silicon carbide on silicon using methylsilane

Cubic SiC thin films have been epitaxially grown on silicon substrates using the single source precursor methylsilane (H₃Si–CH₃). Single phase films were grown by supersonic jet epitaxy (SJE) at temperatures as low as 560°C on Si(111) and 600°C on Si(001). Growth rates and crystal quality were found to be strongly dependent on substrate temperature and methylsilane kinetic energy. Films were characterized by X-ray diffraction (XRD) and cross-sectional transmission electron microscopy (XTEM).     

Real-time synthetic aperture sonar imaging using a parallelarchitecture

This paper describes a parallel architecture that has been developed to perform real-time synthetic aperture sonar imaging as part of the Acoustical Imaging Development (ACID) project. The project has successfully developed a synthetic aperture sonar system for producing high resolution images of the sea floor and that has been tested during a series of sea trials in May 1993 off the south coast of France. This paper describes the synthetic aperture processing system developed by the University of Newcastle upon Tyne and its use of transputer modules and associated devices in order to obtain real-time imaging performance, the software structure of the processing system and the load balancing techniques that have been developed in order to provide efficient processing. The use of a parallel distributed architecture has also allowed a processing system that can readily be extended to deliver greater computational power in the future. Images produced by the synthetic aperture processor from data collected from around the Toulon coastal region are presented. These images highlight the improvement in azimuth resolution that can be obtained from synthetic aperture processing over conventional sidescan sonars.     

Noise-resistant pulse oximetry using a synthetic reference signal

We describe a noise-resistant pulse oximetry algorithm suited to both signal reconstruction and oxygen saturation estimation. The algorithm first detects relatively clean signal sections from which the heart rate is estimated. The heart rate is used to construct a synthetic reference signal that matches an idealized pulse signal. An adaptive filter continuously processes the sensor signals, reconstructing signals in a linear subspace defined by the reference signal. A projective subspace algorithm is then applied to find the oxygenation level of the blood. We show that under specific circumstances this algorithm solves the sufficiency condition for signal reconstruction in linear saturation estimators. The core principle of using a frequency modulated synthetic reference signal can be applied to adaptive filtering of other physiological signals controlled by the heartbeat, such as blood pressure and electrocardiogram.     

Multielement synthetic transmit aperture imaging using temporal encoding

A new method to increase the signal-to-noise ratio (SNR) of synthetic transmit aperture imaging is investigated. The approach utilizes multiple elements to emulate a spherical wave, and the conventional short excitation pulse is replaced by a linear frequency-modulated (FM) signal. The approach is evaluated in terms of image quality parameters in comparison to linear array imaging. Field II simulations using an 8.5-MHz linear array transducer with 128 elements show an improvement in lateral resolution of up to 30% and up to 10.75% improvement in contrast resolution for the new approach. Measurements are performed using our experimental multichannel ultrasound scanning system, RASMUS. The designed linear FM signal obtains temporal sidelobes below -55 dB, and SNR investigations show improvements of 4-12 dB. A 30 mm (approximately 45%) increase in penetration depth is obtained on a multitarget phantom with 0.5 dB/[cm MHz] attenuation. Furthermore, in vivo images of the abdomen are presented, which demonstrate the clinical application of the new approach.