The backscattered field of a thin wire loop for H-polarization

For a thin wire loop illuminated by a plane electromagnetic wave, the backscattered field is determined when the incident magnetic vector is parallel to the plane of the loop. The complete second-order geometrical theory of diffraction (GTD) solution is obtained and found to be in excellent agreement with numerical data at angles close to normal incidence on the loop. At wide angles, however, the data exhibit a significant lobe that is not predicted by GTD. Analysis of the data shows that the lobe is due to currents circulating around the loop and the properties of these currents are deduced. Using a simple model for the current, the corresponding contribution to the backscattered field is determined. When this is added to the GTD solution, the resulting expression for the backscattered field is in good agreement with the numerical data for all angles of incidence and all loop diameters greater than a wavelength.     

Wire bond loop profile development for fine pitch-long wireassembly

Die size reductions can be achieved through “optical shrinks,” compaction of existing layouts, or redesigns to finer fab geometries. For some die the limiting factors for die size reduction are bond pad pitch and bond pad size. In these “pad limited” designs, the circuitry is concentrated in the center of the die. Precious empty space exists between the bond pads in the periphery of the die and the circuitry in the die core. The only hope for die size reductions in these designs lies in advances in assembly technology that allow for reductions in bond pad pitches and bond pad size. Fine pitch assembly poses a number of challenges for conventional wire bond technology. Reducing bond pad pitch increases the probability of ball shorting, bond wire shorting, and bond wire damage. On the other hand, decreasing the die size by reducing the bond pad pitch results in longer wire lengths thus limiting some assembly options such as moving to smaller diameter bonding wires. Wire loop profile becomes a critical factor for control in fine pitch assembly. In this paper a statistical design of experiment is used in developing a wire bond loop profile control. The effect of major bonding parameters, such as kink-height, reverse loop, loop factor, wire tension, and their impact on loop profile are analyzed. The results obtained define the bond parameter requirements that must be met in order to control the wire loop profile to optimize fine pitch wire bond assembly yields     

键合线弧高度对键合拉力的影响分析

在集成电路封装的质量控制中,键合拉力的地位非常重要。作为键合质量好坏的主要判定基准之一,影响键合拉力的因素有很多,包括键合工艺参数、焊线材料类型、拉力测试吊钩的测试位置、焊线线径以及线弧的长度和高度等。主要讨论在键合线弧投影长度不变的情况下,线弧高度的变化对键合拉力产生的影响。通过对不同线弧高度条件下测得的拉力数据进行整理分析,结果表明:键合线弧越高,拉力就越大;反之,拉力则越小。这为集成电路组装的正常量产过程中,工程技术人员对于键合线弧整体高度的合理有效控制及键合拉力规范的合理定义提供了参考依据。     

钢丝绳传动在航空光学遥感器上的应用

针对某航空光学遥感器扫描组件和消旋组件需以高精度同步旋转的要求,提出一种通过双电机驱动,采用独立的位置环和速度环控制的钢丝绳精密传动方法。首先,详细介绍了钢丝绳精密传动的结构形式和控制方法,并简要分析了钢丝绳的传动刚度,最后,通过实验对钢丝绳精密传动的精度进行测试,同时分析了预紧力和负载力对精度的影响。实验结果表明:本钢丝绳精密传动系统实现了扫描组件和消旋组件旋转同步精度0.03°,旋转速度为5°/s时稳速精度达1.5%,满足设计要求。实验结果验证了本钢丝绳精密传动应用方法的可行性,为钢丝绳精密传动在航空光学遥感器上的应用提供了一种新的方法。     

Electromagnetic loop vehicle detectors

Three different electromagnetic loop vehicle detector designs are described: self-tuning, bridge balance, and phase-shift. Principles of operation, design limitations, and design trade-offs for each method are presented in detail. The characteristics of the lead-in wire used are shown to be the primary limitation in loop detector performance and stability. Characteristics of commercially available wire used in present-day loop detector installations are discussed. Design equations and graphs illustrate the tradeoff considerations in the determination of optimum loop configuration and inductance.     

RCS of resonant scatterers with attached wires

The effects of wire antennas carried on aircraft for HF communication on the radar cross section (RCS) at HF frequencies are studied by comparing the RCSs of a strip, a cylinder, and a rod with and without an attached wire. The RCS is found for broadside incidence and for end-on incidence of the plane wave for scatterer lengths from 0.4 to 3.8 wavelengths, typical of aircraft size at HF frequencies. It is shown that the RCS of such fuselage-like targets with a wire antenna is quite different from that of the targets without the wire. For broadside incidence, the wire contributes a sharp peak-and-trough to the RCS are the wire's fundamental resonant frequency. For end-on incidence the wire considerably enhances the RCS at frequencies making its length odd multiples of the quarter-wave     

Design in triangle-profiles and T-profiles of a wirebond using alinkage-spring model

Different profiles of a wirebond utilizing a linkage-spring model are proposed in this paper, and loop heights are minimized in order to prevent wire sweep during molding. To analyze loop profiles, a nonquantitative, time-consuming, experimental statistical method was applied in previous studies. Although the finite element model is the most powerful tool in stress analysis, it is more complex in analyzing a large deformation as compared to the linkage-spring model. The purpose of this paper is to simulate the capillary trajectory from the first bond to the second bond stages by a linkage-spring model developed by Lo, and then to discover the proper wirebond trajectories. To meet with the gold wire properties, the transient temperature distribution along the gold wire during the bonding process is considered, Accordingly, the spring constants in a linkage-spring model are modified along the wire. Furthermore, the design rules in the looping process are defined and four examples of triangle- and T-profiles of a wirebond are also presented     

海底瞬变电磁探测技术的装置参数研究及实验

可控源时间域电磁法应用在海底探测,需要确定装置参数,通过实验和理论计算确定了发射频率的最大值;分析了发射线圈的电性对发射电流后沿的影响,确定了作为发射线圈的导线的时间常数应尽量小;对接收线圈的参数及过渡过程进行了理论分析和室内模型实验,理论计算了接收线圈电路模型在发射电流斜阶跃下降和关断后在欠阻尼、临界阻尼和过阻尼状态的一次感应电动势解的情况,确定了采用并联匹配电阻消除振荡的方法,并依据所分析的装置参数设计实施了海上实验,探测出海底低阻体的准确位置.     

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.     

The near field of annular antennas

The circular loop antenna has been investigated by many authors beginning as early as 1897 with Pocklington's study of the thin wire loop excited by a plane wave. Later, both Hallen and Storer considered the case of driven antennas. All of these authors used a Fourier series expansion for the loop current, and the latter two found numerical difficulties with the approach. These difficulties, as pointed out by Wu, can be avoided by integration of the free-space Green's function over the toroidal surface of the wire. The theory developed here is an improvement on previous works because it specifically takes into account the finite dimension of the wire. Consequently, the range of validity for our solution extends to fatter wires than previously considered. Furthermore, some detail of the loop current around the cross section of the wire is revealed. The theory, if applied to thin wire loops, gives radiation admittances in excellent agreement with results obtained by previous investigators. The computations of the electromagnetic fields near resonant loops show that the electric field strength is larger by a factor of ten than previously published values. Experimental results validate the theory presented in the following sections.     

Folded loop antenna for mobile hand-held units

The vertical folded loop antenna, modeled as wire and printed radiating element mounted on a conducting box, simulating a cellular telephone with and without dielectric coating, is analyzed. The finite-difference time-domain (FDTD) method is used to calculate radiation patterns and input impedance. The results are compared with measurements and with NEC data. Very good agreement is obtained in all cases. Parasitic loading is used to enhance the bandwidth of the printed element. The antenna meets the design requirements for existing and future mobile communication systems     

Process and design analysis for ultrafine-pitched wiresweep elimination in advanced copper heat spreader BGA package

The semiconductor device trend for increasing functionalities and performances yet with smaller overall feature sizes presents escalating obstacles to the decreasing form factor along with demanding thermal carrying capability required at the package level. To confront this compounding issue, ultrafine-pitch wirebond interconnect coupled with thermally enhanced copper heat spreader attached to the package are introduced. However, the additional copper heat spreader thickness introduced within the package challenges the design of the package's wire, its loop height, and the molding process control to prevent wire sweeping occurrences. This study investigates the impact of different ultrafine pitched wire types, wire loop designs, copper heat spreader structures, and mold material types on eliminating device short from occurring due to the wire sweeping phenomena. A full factorial experiment is performed using an active silicon device packaged in a thermally enhanced ball grid array (BGA) test vehicle. In addition, test characterization is carried out using x-ray and multiinsertions hot/cold continuity tests. Then, a detailed failure analysis is performed by package decapsulation and scanning electron microscopy/energy-dispersive x-ray (SEM/EDX) to confirm the experimental findings. In conclusion, the study finds that for an ultrafine-pitched thermally enhanced BGA package, wire type is insignificant to reduce wire shorting occurrences. However, mold material and copper heat spreader structure using an optimized wire loop design are significant factors in eliminating wiresweep shorting phenomena. This study concludes with a wirebond interconnect and heat slug design recommended along with an improved process parameters and assembly material sets found from the experiment.     

Insulated loop antenna in a conducting spherical shell

Wait has calculated the impedance seen by a small circular loop of wire placed in an insulating spherical cavity in an infinite homogeneous conducting dielectric. The same technique may be used to compute the impedance of a loop inside a spherical shell. Attention is focused on the change in impedance of an electrically small wire loop when it is placed inside a spherical shell of lossy dielectric material whose radius is small compared to the free-space wavelength. The self-impedance in the absence of the shell can be calculated separately. Simple formulas are developed for the case where the conduction currents in the shell dominate over displacement currents and the shell is thin compared to the skin depth.     

The use of curved segments for numerically modeling thin wireantennas and scatterers

To reduce the number of segments required to model curved wire structures, a method of moments formulation using curved wire segments is presented. Piecewise quadratic wire segments are used to discretize the wire geometry. This algorithm is used to analyze a small wire loop antenna and multiple-arm Archimedian spiral antenna. For each example, a comparison is made between results obtained using this quadratic segment algorithm and a linear segment algorithm. These examples demonstrate that the memory required is significantly reduced and a reduction in the solution time is achieved when quadratic segments are used     

Analytical antenna model for chiral scatterers: comparison withnumerical and experimental data

An analytical model for polarizability dyadics of small chiral conductive particles in free space or those embedded in a lossy material is presented and discussed. Chiral particles are modeled by a wire loop connected to two straight wire elements. The electromagnetic analysis is based on the replacement of the particles by two connected antennas representing the wire and loop portions. Analytical expressions for polarizabilities are given. For electrically small particles, a lumped-element equivalent circuit can be constructed and the polarizabilities can be expressed in terms of equivalent circuit parameters. It is shown that the wire-and-loop antenna model for scatterers satisfies the reciprocity condition and other basic physical requirements. Approximate analytical expressions are compared with numerical simulations and with the experimental data on reflection from single chiral particles, and the results are seen to be in good agreement. The model can be used in analytical modeling of chiral and omega composite materials     

引线键合中第一点勾线力的影响因素

勾线拉力测试是评估引线键合质量的一种主要方法,同时影响测试结果的因素有很多.文章通过理论分析和实际测量,发现封装结构、线弧高度和勾线位置对第一焊点的勾线力有显著影响.Non-EP结构中线弧的第一点勾线力比EP结构中的大;随着线弧高度的增加,线孤的第一点勾线力将逐渐变大;在勾线位置由第一焊点逐渐移至线弧中间位置时,一般高...     

Finite-Difference Analysis of EMP Coupling to Thin Struts and Wires

This paper describes the implementation of the thin-strut formalism in the 3-D EMP time-domain finite-difference code THREDE. The thin-strut formalism permits inclusion of arbitrary fine wires in THREDE without imposing any corresponding demand to reduce the cell size to the wire size. The keystone of this technique is the so-called in-cell inductance-the inductance per unit length a thin wire would have with respect to an enclosing conductor half a cell removed. THREDE results using this formalism are compared with analytic EMP solutions for a linear dipole antenna and a loop antenna. Errors are around 10 percent for the loop and 7 percent for the dipole. The 10-percent loop error could probably be improved; the 7-percent dipole error seems to be fundamental to the basic THREDE approximations.     

On a new cylindrical harmonic representation for spherical waves

An exact series representation is presented for integrals whose integrands are products of cosine and spherical wave functions, where the argument of the cosine term can be any integral multiple n of the azimuth angle φ. This series expansion is shown to have the following form: I(n)=e^-jkR0/R₀ δ_no-jk Σ_m=1^∞ C(m,n)(k ²ρρ0)/m! h_m⁽²⁾(kR₀)/(kR₀)^m . It is demonstrated that in the special cases n=0 and n=1, this series representation corresponds to existing expressions for the cylindrical wire kernel and the uniform current circular loop vector potential, respectively. A new series representation for spherical waves in terms of cylindrical harmonics is then derived using this general series representation. Finally, a closed-form far-field approximation is developed and is shown to reduce to existing expressions for the cylindrical wire kernel and the uniform current loop vector potential as special cases     

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.