Optimizing resistance of round hollow wire at high frequency

The results and methods of calculation of resistance of hollow wire in gigahertz range by Bessel function are given. According to the results of computation, it is found that the resistor of conductor can be optimized using hollow wire with specific wall thickness. At high frequency the current distribution across a circular hollow wire is at surface of wire, which is called skin depth. We found that optimum wall thickness is proportional to skin depth and the phase abrupt change point of H field. Theoretical analysis and mechanism optimized round hollow wire will be presented in this paper. The calculation indicates that cylindrical hollow wire can be optimized to decrease resistance above 8%.     

Frequency-related effects in the optimization of coils for the magnetic stimulation of the nervous system

Magnetic stimulation of the nervous system is a non-invasive technique with a large number of applications in neurological diagnosis, brain research, and, recently, therapy. New applications require engineering modifications in order to decrease power consumption and coil heating. This can be accomplished by optimized coils with minimized resistance. In this study the influence of some frequency-related effects (skin and proximity effect) on the coil resistance will be discussed, together with the role played by wire shape, wire section, and twisting effect. The results show that the coil resistance increases with frequency. As an example, for a 20-mm2 circular wire section, the skin effect in the typical frequency range of magnetic stimulator devices (2-4 kHz) increases the coil resistance up to about 45% with respect to its dc value. Moreover, the influence of the frequency is lower for flat wire sections and reasonably small helix twist angle of the coil.     

Heat Loss of Circular Electric Waves in Helix Waveguides

This paper presents a theoretical calculation of the eddy current losses of circular electric waves in a closely-wound helix waveguide. The wire diameter is assumed large compared to the skin depth, but small compared to the guide diameter and the operating wavelength, so that the fields near the wire are quasistatic and may be determined by conformal mapping. When the wires are in contact, the waveguide wall is effectively a metal surface with grooves of semicircular cross section, the current flow being parallel to the direction of the grooves. The power loss for this case is computed to be about 8.5 per cent higher than in a waveguide with smooth metal walls. When the wires are not in contact, the wall is treated as a grating of parallel, round wires. The increase in power loss over a smooth surface is approximately 22.5 per cent when the wires are separated by a distance equal to their diameter.     

Experimental investigation on liquid-phase fabrication techniques for multilayer infrared hollow fiber

Infrared hollow fiber with metal and dielectric inner-coatings has found applications in medical and industrial fields. It is a commonly used method to lower the loss by inner-coating multi dielectric layers. In this paper, SiO₂ and AgI were selected to fabricate the multilayer mid-infrared hollow fiber. Liquid-phase coating techniques were experimentally discussed in order to control the film thickness. It is shown that concentration and flow speed of the coating solution are key parameters to modify SiO₂ film thickness. AgI film was obtained by firstly coating a silver layer and then iodinating the silver layer into AgI. SiO₂ and AgI films were deposited orderly on the inner wall of a 0.7-mm bore glass capillary. Both thicknesses for SiO₂ and AgI films were well controlled and optimized according to the theoretical calculation. The measured infrared loss spectrum of SiO₂/AgI/SiO₂/Ag multilayer hollow fiber has a good agreement with the calculated result and shows band gap effect around the wavelength of 5.3 μm.     

声表面波在空心圆柱体中的传播特性分析

空心圆柱体管道类的声表面波检测是目前工程检测领域常见的问题.通过势函数和位移假设,建立了声表面波在空心圆柱体内传播的频散方程.数值计算结果表明在空心圆柱体内传播的声表面波与平板中传播的兰姆波存在类似,位移表现为对称和反对称模态.随着频率的增加,低阶模态的相速度逐渐趋于声表面波波速,同时空心圆柱体的壁厚对声表面波相速度的...     

Improving thermal performance of miniature heat pipe for notebook PC cooling

A miniature heat pipe (MHP) with woven wire wick was used for cooling a notebook PC. The cross-sectional area of the pipe is reduced by about 30% of the original, when the diameter of the MHP is pressed from 4 to 2 mm for packaging in a notebook PC. In the present study, a test of the MHP has been performed in order to review the thermal performance by varying pressed thickness, total length of MHP, wall thickness, heat flux and inclination angle. New wick types were considered for overcoming low heat transfer limits, which occur when the MHP is pressed to a thin plate. Through a performance test, the limiting thickness of pressing is shown to be within the range of 2–2.5 mm. When the wall thickness of 0.4 mm is reduced to 0.25 mm for minimizing conductive thermal resistance through the wall of heat pipe, the heat transfer limit and thermal resistance of the MHP were improved about 10%. While the thermal resistance of the MHP with central wick type is lower than that of the MHP with circular oven wire wick, the thermal resistance of the MHP with composite wick of woven/straight wire is higher than that of the MHP with circular woven wire wick. From the performance test conducted on the MHP cooling modules with woven wicks, it is seen that the T_jc (junction temperature of the processor) satisfies a demand condition of being between 0 and 100 °C. This shows the stability of the MHP as a cooling system of notebook PCs.     

Experiment study on electroplated diamond wire saw slicing single-crystal silicon

This paper conducted the slicing experiments of single-crystal silicon using a reciprocating electroplated diamond wire saw. The machined wafer topography and wire wear were observed by using scanning electron microscope (SEM). The influences of process parameters and cutting fluids on single-crystal silicon wafer surface roughness (SR), subsurface micro-crack damage (SSD) depth, total thickness variation (TTV) and warp were investigated. The bonded interface sectioning technique was used to examine the cut wafers SSD depth. Study results show that a higher wire speed and lower ingot feed speed can produce lower wafer SR and SSD; the lower warp of wafer needs lower wire speed and ingot feed speed; and low wafer TTV can be obtained by an appropriate matching relationship between wire speed and ingot feed speed. The synthetic cutting fluid has a better total effect to improve the wafer quality. The pulled-out of diamond abrasives is the main wear form of wire, which indicates that more research on improving the abrasives retaining strength on wire surface should be investigated in fixed-abrasive wire manufacturing process, in order to improve the wire life and wire saw machining process.     

Electromagnetic scattering by a straight thin wire

The traveling-wave energy, which multiply diffracts on a straight thin wire, is represented as a sum of terms, each with a distinct physical meaning, that can be individually examined in the time domain. Expressions for each scattering mechanism on a straight thin wire are cast in the form of four basic electromagnetic wave concepts: diffraction, attachment, launch, and reflection. Using the basic mechanisms from P.Ya. Ufimtsev (1962), each of the scattering mechanisms is included into the total scattered field for the straight thin wire. Scattering as a function of angle and frequency is then compared to the moment-method solution. These analytic expressions are then extended to a lossy wire with a simple approximate modification using the propagation velocity on the wire as derived from the Sommerfeld wave on a straight lossy wire. Both the perfectly conducting and lossy wire solutions are compared to moment-method results, and excellent agreement is found. As is common with asymptotic solutions, when the electrical length of wire is smaller than 0.2 λ the results lose accuracy. The expressions modified to approximate the scattering for the lossy thin wire yield excellent agreement even for lossy wires where the wire radius is on the order of skin depth     

Low-frequency impedance of a circular loop over a conducting ground

Using a quasistatic approach, the input impedance of a circular wire loop is calculated for the case where the Earth is represented as a homogeneous conducting halfspace. It is shown that the input resistance is only proportional to the ground conductivity when the loop radius is small compared with the electrical skin depth.     

The influence of boundary conditions on the electrical conductivity of a thin cylindrical wire

Within the kinetic approach, the high-frequency electrical conductivity of a thin semiconductor circular cross-section wire is calculated. The radius of the wire is assumed to be small compared with the characteristic skin depth that allows neglecting the skin effect. A model taking into account the dependence of the reflectivity coefficient on the surface roughness factor and the angle of incidence of the charge carriers at the inner border of the wire was used as the boundary conditions for the nonequilibrium distribution function of the charge carriers The extreme cases of a degenerate semiconductor and a nondegenerate one are considered. The results obtained are compared to the calculations for the model of Fuchs diffuse-specular boundary conditions.     

Axial-line-current approximation for short cylindrical wires

A commonly used approximation in calculating the self impedance of a short cylindrical wire is to assume that current flows along its axis only. Numerical results are presented that quantify the error in the vector potential arising from this line-current assumption for small length/diameter ratios of the wire, provided that the skin depth is very much less than the wire radius.     

镀银铜线的银层厚度与银质量分数换算

从镀银铜线银层厚度的设计原理出发,推导了镀银铜线的银层厚度与银的质量分数之间的换算公式。并与ASTM13298、JB3135标准所列公式相比较,发现推导出的公式能更好地显示其本质,计算结果更为精确。列出的数据可供镀银铜线生产商方便地使用。     

Mechanisms of wafer sawing and impact on wafer properties

Silicon wafer wire‐sawing experiments were realized with different sets of sawing parameters, and the thickness, roughness, and cracks depth of the wafers were measured. The results are discussed in relation to assumptions underlying the rolling–indenting model, which describes the process. It was also found that the silicon surface at the bottom of the sawing groove is different from the wafer surface, implying different sawing conditions in the two positions. Furthermore, the measured parameters were found to vary along the wire direction, between the entrance of the wire in the ingot and its exit. Based on these observations, some improvements for the wire‐sawing model are discussed. Copyright © 2010 John Wiley & Sons, Ltd.     

Modeling and optimization of via formation in dielectrics by laser ablation using neural networks and genetic algorithms

Laser ablation is an effective process for forming vias in dielectric layers during the fabrication of multilayer substrates in microsystems packaging. In this paper, vias with diameters of 10-50 /spl mu/m are ablated in DuPont Kapton E polyimide using an Anvik HexScan 2150 SXE excimer laser operating at 308 nm. A statistical experiment employing a 2/sup 5-1/ fractional factorial design is conducted to determine the significance of laser fluence, shot frequency, number of pulses, and the vertical and horizontal positions of the debris removal system on the ablated thickness of the dielectric, top via diameter, via wall angle, and via resistance. Resistance measurements on metal deposited in ablated vias are performed to characterize via quality. Neural networks (NNs) are trained using the error back-propagation algorithm to model the ablation process using the measurement data collected from the experiment. Genetic algorithms are then utilized in conjunction with the NN models to derive optimized process recipes for achieving target responses. The recipes identified are subsequently verified by experiment. These optimized recipes are found to improve ablation results by as much as 40% for the ablated film thickness, 30% for via diameter, 9% for via wall angle, and more than 100% for via resistance.     

基于红外热像的网架焊接空心球节点疲劳试验研究

焊接空心球网架结构被广泛使用在带悬挂吊车的工业厂房中。悬挂吊车带来的往复交变荷载会造成网架焊接节点的疲劳破坏。在焊接空心球节点的疲劳试验过程中,借助红外热像仪记录试件表面的温度,得到了试件表面的温升分布,温升高区位于钢管与焊接球的焊接连接球面焊趾处,此区域对应节点最后的疲劳破坏位置。在疲劳试验过程中,焊趾处的温升高区位置几乎不变,当疲劳裂纹穿透球壁厚时,温升高区的位置发生变化。试验表明:红外热像仪可以实时记录焊接空心球节点试件在疲劳试验过程中表面的温度,通过分析温升高区在没有可见裂纹的情况下就可预测疲劳破坏发生的位置,温升高区位置的变化对应裂纹贯穿球壁时节点试件的疲劳寿命。     

Process windows for low-temperature Au wire bonding

The process windows are presented for low-temperature Au wire bonding on Au/Ni/Cu bond pads of varying Au-layer thicknesses metallized on an organic FR-4 printed circuit board (PCB). Three different plating techniques were used to deposit the Au layers: electrolytic plating, immersion plating, and immersion plating followed by electrolytic plating. Wide ranges of wire bond force, bond power, and bond-pad temperature were used to identify the combination of these processing parameters that can produce good wire bonds, allowing the construction of process windows. The criterion for successful bonds is no peel off for all 20 wires tested. The wire pull strengths and wire deformation ratios are measured to evaluate the bond quality after a successful wire bond. Elemental and surface characterization techniques were used to evaluate the bond-pad surfaces and are correlated to wire bondability and wire pull strength. Based on the process windows along with the pull strength data, the bond-pad metallization and bonding conditions can be further optimized for improved wire bondability and product yields. The wire bondability of the electrolytic bond pad increased with Au-layer thickness. The bond pad with an Au-layer thickness of 0.7 μm displayed the highest bondability for all bonding conditions used. The bondability of immersion bond pads was comparable to electrolytic bond pads with a similar Au thickness. Although a high temperature was beneficial to wire bondability with a wide process window, it did not improve the bond quality as measured by wire pull strength.     

Shielding effectiveness of rectangular cavity made of a new shielding material and resonance suppression

New shielding material has become an alternative to traditional metal to shield boxes from electromagnetic interferences. This article introduces the theory of transmission line method to study the shield boxes made of a new sort of material, and then expands the fundamental formulas to deal with the cases of multiple holes and polarization with arbitrary angle. By means of genetic algorithms with the aid of a three dimensional simulation tool, the damping of electromagnetic resonances in enclosures is researched. The computation indicates that under resonant frequency, electromagnetic resonance results in low, even negative shielding coefficient; whereas, for the same areas, shielding effectiveness of a single hole is worse than that of multiple holes. Shielding coefficient varies when polarization angle increases, and the coupled field through the rectangular aperture with the long side parallel to the thin wire is much weaker than that with the long side vertical to the thin wire. By using the metallic-loss dielectric layer of optimized calculation on the internal surface of the cavity, the best result of resonance suppression has been realized with the same thickness of coating. Finally, according to the calculation result, suggestions for shielding are proposed.     

Thermal performance of collector-up HBTs for small high-power amplifiers with a novel thermal via structure underneath the HBT fingers

We will describe the thermal performance of a special heterojunction bipolar transistor (HBT) structure for mobile communication systems, called a collector-up HBT. We calculated the thermal resistance between the HBT fingers and the bottom surface of a GaAs substrate using a finite element method (FEM). The results suggest that the thermal resistance of collector-up HBTs with thermal via structures can be reduced by 64% compared to the thermal resistance of ordinary emitter-up HBTs. They also show that the thickness of the InGaP emitter layer effects the thermal resistance of, and the temperature distribution in, the collector fingers of collector-up HBTs. Even though the thermal resistance of collector-up HBTs can be much smaller than that of emitter-up HBTs, a thermal interaction between the collector fingers still exists in multi-finger structures. We analyzed the temperature distribution in the collector fingers of a four-finger HBT structure and found that the thickness of the plated heat sink (PHS) was not sufficient to reduce the thermal interaction between the HBT fingers, and that optimization of the HBT location was needed to minimize the thermal interaction. We also found that the thickness of the InGaP emitter layer was the most important parameter for reducing thermal resistance, even in four-finger HBT structures. These calculation results can be used to reduce the temperature of collector-up HBTs and the temperature differences between the HBT fingers in the development of power amplifiers with collector-up HBTs.     

Determination of reactance loading for circularly polarized circular loop antennas with a uniform traveling-wave current distribution

A simple theory is presented to predict the lumped reactance loading for circularly polarized circular loop antennas with a uniform traveling-wave current distribution. The reactive load is located on a circular wire loop of one-wavelength circumference at a position of 45/spl deg/ away from the feed point. To achieve a uniform traveling-wave current distribution, the loading reactance and the input impedances of the loaded and unloaded loop antennas need to satisfy certain conditions. First, the input resistance and the input reactance of the unloaded loop antenna should have the same absolute value. Second, the input impedance of the loaded loop must be purely resistive and its value needs to be two times of the input resistance of the unloaded loop. Third, the loading reactance should be chosen to be two times in value and opposite in sense of the input reactance of the unloaded loop. These conditions can be approximately met when the circular loop is placed above a ground plane. The loading reactance is determined from the input impedance of the unloaded loop and is optimized for an optimal performance of circular polarization. It is found that the reactive load must be capacitive and its value depends on the height of the loop above the ground plane and the thickness of the wire. The characteristics of the circular polarization and the input impedance of the capacitance-loaded circular loop antennas are investigated. An experimental example is presented to verify the theoretical prediction.     

聚焦光声鲜红斑痣诊断技术的模拟实验研究

对鲜红斑痣皮肤(PWS,port wine stain)的客观评估是应用激光成功治疗PWS的关键.本文提出了一种基于聚焦换能器的光声深度分辨技术来实现对PWS皮肤的评估.通过利用聚焦换能器,该技术不但可以实现定位病灶位置的目的,还可以减少非聚焦区光声信号的干扰.模拟样品测试结果表明,聚焦光声深度分辨技术可实现对PWS皮肤的病灶深度、表皮黑色索含量以及病变层厚度的有效检测.初步的实验结果显示了该技术在PWS皮肤诊断方面的应用前景.