Simplified triangular ground plane cloak by oblique multilayer dielectrics

Based on the effective medium theory, the triangular ground plane cloak can be realized by thin layered systems. Two solutions of parameter setting of the layered cloak are suggested to demonstrate the invisibility performance of a hybrid incoming wave. The hybrid parameters are derived from the equivalent of both anisotropies of permittivity and permeability to the Mternating layers. The performance of the designed layered cloak is validated by both TM and TE wave simulations with near-field distributions and average scattering power outflows on an observation semicircle. From the simulation results, the layered cloak with both hybrid parameters and improved hybrid parameters can reflect the incoming TM/TE waves in a specular direction, and the latter behaves with a better overall invisibility performance.

Stitched Ground Planes for Textile Antenna Application: An Experimental Study

This paper presents an application of stitched ground plane for microstrip patch antenna design. In this work Matlab interface to computer embroidery techniques were used to implement the felt and denim substrates on microstrip patch antenna. These antennas were simulated using a commercial full 3D electromagnetic CST Microwave Studio 2019. A method to optimize the stitch patterns with conductive thread for antenna ground plane for 2.45 GHz industrial, scientific, and medical (ISM) band and 5 GHz wearable wireless local area networks (WLAN) frequencies was achieved. Rigid and flexible wearable antennas (microstrip patch antennas) were fabricated using the stitched ground plane. The electrical resistance was reduced between the meshes during the stitching design process. Results in terms of bandwidth, radiation patterns and reflection coefficients (S11) are presented.

Novel Stitched Ground Plane Optimizations for Microstrip Patch Antennas at Wi-Fi and WiMAX Applications

This work explores the optimal mesh structure, stitch density and production technique of stitched ground plane for microstrip patch antenna. Meshed ground plane was used as a generic problem. A stitched ground plane is pro-posed and designed using Matlab interface to computer embroidery. Using the meshed or stitched ground plane as a case study, the resistance between meshes was analysed and measured. The equivalent resistance between nodes is a function of their distance apart. A finite resistive grid was simulated and compared to measured sets of data. A microstrip patch antenna with stitched ground shows comparable performance to the conventional etched ground of the size in terms of bandwidth. The stitched ground plane has a higher band-width than the etched copper ground plane because of the increased thickness of the substrate. Thus, it can be concluded that the use of the interface method shows the possibilities of controlling the stitch density and distances between mesh nodes. The interface increases the stitching density and reduces the elec-trical resistance between mesh nodes making the antennas flexible and weara-ble. The functionality of these antenna samples has been tested and validated using microstrip patch ground at 2.45 GHz and 5 GHz. Measurement results on the proposed stitched ground planes were compared with the theory of infinite resistive network that shows good agreement.

Effect of Partial Ground Plane Removal on the Radiation Characteristics of a Microstrip Antenna

This study presents a new, simple method for reducing the back-lobe radiation of a microstrip antenna (MSA) by a partially removed ground plane of the antenna. The effect of the partial ground plane removal in different configurations on the radiation characteristics of a MSA are investigated numerically. The partial ground plane removal reduces the backlobe radiation of the MSA by suppressing the surface wave diffraction from the edges of the antenna ground plane. For further improving the front-to-back (F/B) ratio of the MSA, a new soft-surface configuration consisting of an array of stand-up split ring resonators (SRRs) are placed on a bare dielectric substrate near the two ground plane edges. Compared to the F/B ratio of a conventional MSA with a full ground plane of the same size, an improved F/B ratio of 9.7 dB has been achieved experimentally for our proposed MSA.

Rectangular Microstrip Antenna on Ridge Ground Plane to Control the Resonant Modes for Improved Bandwidth using Transverse Resonance Method

A single layer single element rectangular microstrip antenna on ridge ground plane for improved bandwidth is theoretically investigated with a view to develop a concrete physical insight in to the phenomenon. The simple single element probe fed rectangular microstrip antenna fabricated on conventional PTFE (Poly Tetra Fluride Ethelene) substrate have many advantages except its narrow bandwidth. The present study proposes the technique to control the resonant modes of a microstrip antenna for yielding better bandwidth using transverse resonance method. The present antenna is designed to fabricate on ridge ground plane which has been compared with conventional structure and around 6% - 7% improvement in bandwidth is revealed. The detailed variation of radiation pattern across its frequency band has been studied and presented in this paper. The proposed idea has been verified through a commercial software package (High Frequency Structure Simulator) for a patch operating in X band and explained quantitatively. The electric surface current distribution over the patch surface for both the conventional and proposed antenna is presented to explain the broad banding effect physically.

Microfabricated ultra-thin all-polymer thermal ground planes

Abstract Thermal ground planes, or planar heat pipes, can provide highly effective heat transfer by utilizing phase change of an encapsulated fluid. In this article, a flexible thermal ground plane （FTGP） was fabricated using poly- mer materials. Kapton was employed as a casing material while micropatterned SU-8 was used to provide both a liquid wicking structure and pillars to support the casing over a vapor core. An ultra-thin TiO2 film was deposited over the SU-8 and Kapton via atomic layer deposition, which acted as both a moisture barrier and a hydrophilic coating on polymer surfaces. The assembled FTGP has a thickness of 0.30 mm, an active area of 20 mm~ 60 mm, heater area of 20 mm x 10 ram, and can operate with a heat load up to 9.54 W, with an effective thermal con- ductivity up to 541 W/（m K）.

Amplification of in-plane seismic ground motion by group cavities in layered half-space (Ⅱ): with saturated poroelastic soil layers

As the continuation study on amplification of in-plane seismic ground motion by underground group cavities in layered half-space, this study extends to the case of poroelastic half-space with dry poroelastic and saturated poroelastic soil layers. The influence of poroelastic layers on the amplification of seismic ground motion is studied both in frequency domain and time domain using indirect boundary element method （IBEM）. It is shown that for the example of a saturated poroelastic site in Tianjin under the excitation of Taft wave and E1 Centro wave, the amplification of seismic ground motion in poroelastic case is slightly smaller than that in the elastic case, and the amplification of PGA （peak ground acceleration） and its PRS （peak response spectrum）.. can be increased up to 38.8% and 64.6%; the predominant period of response spectra in poroelastic case becomes shorter to some extent compared with that in the elastic case. It is suggested that the effect of underground group cavities in poroelastic half-space on design seismic ground motion should be considered.

Amplification of in-plane seismic ground motion by group cavities in layered half-space (Ⅰ)

Amplification of in-plane seismic ground motion by underground group cavities in layered half-space is studied both in frequency domain and time domain by using indirect boundary element method （IBEM）, and the effect of cavity interval and spectrum of incident waves on the amplification are studied by numerical examples. It is shown that there may be large interaction between cavities, and group cavities with certain intervals may have significant amplification to seismic ground motion. The amplification of PGA （peak ground acceleration） and its PRS （peak response spectrum） can be increased up to 45.2% and 84.4%, for an example site in Tianjin, under the excitation of Taft wave and E1 Centro wave; and group cavities may also affect the spectra of the seismic ground motion. It is suggested that the effect of underground group cavities on design seismic ground motion should be considered.

地面超载下摩擦单桩负摩阻力的连续介质力学解

针对地面超载引起的摩擦单桩负摩阻力,提出了一种基于桩土相互作用和连续介质力学的竖向位移模型来模拟桩土系统位移,模型中包含了桩土轴线位移函数和沿径向的衰减函数;采用变分法得到了桩土系统的总势能,从而得到了位移模型中桩土位移和衰减函数的耦合控制方程;利用迭代法求解了这两个耦合函数,得到了桩身轴力、中性面、负摩阻力、下拉力和土弹簧等效刚度等关键参数的数学表达式;通过和原位试验及已有理论结果的对比,验证了所提方法的正确性。结果表明:桩土模量比对桩的负摩阻力和下拉力有显著影响,中性面位置与长细比密切相关,而与桩土模量比关系不大;随着桩土模量比增大和桩长细比减小,桩身同一位置处轴力增长明显,但增长速率变缓;地面超载作用下桩周土体位移最大沉降出现在地表处,且地表以下0.3倍桩长范围内为位移强烈影响区;桩长细比和桩土模量比的增加均会使桩周土体位移场影响范围增大。

有限大接地板对圆极化微带贴片天线等化波束宽度影响的研究

基于数值仿真和实验测量,研究了接地板尺寸对微带贴片天线圆极化等幅条件的影响规律。结果表明:当接地板尺寸变化时,铅垂极化分量幅度(|E_(θ)|)和水平极化分量幅度(|E_(φ)|)受到地板尺寸变化的敏感度和规律不同,从而影响了圆极化天线主波束范围内保持其幅值相等的条件。最终推得接地板尺寸在0.6~1.0波长范围内,铅垂、水平极化分量保持等幅条件(按幅度差不大于3dB计)的“等化波束宽度”经验公式,为可穿戴圆极化贴片天线的波束宽度调控及选择提供理论依据。

Integrated Guidance and Control of Homing Missiles Against Ground Fixed Targets

This paper presents a scheme of integrated guidance and autopilot design for homing missiles against ground fixed targets. An integrated guidance and control model in the pitch plane is formulated and further changed into a normal form by nonlinear coordinate transformation. By adopting the sliding mode control approach, an adaptive nonlinear control law of the system is designed so that the missile can hit the target accurately with a desired impact attitude angle. The stability analysis of the closed-loop system is also conducted. The numerical simulation has confirmed the usefulness of the proposed design scheme.

基于投影光瞳分布的星地激光通信波前探测

为了解决星地自由空间光学通信系统中的提前角问题,采用了一种基于光强传输的新型波前探测技术——投影光瞳面分布(Projected Pupil Plane Pattern,PPPP),并通过实验室实验验证了该技术的可行性。PPPP基于TIE光强传输公式,根据不同传输距离下光强分布的变化反解出大气湍流引起的波前畸变。由于PPPP采用的是上行通信激光本身的后向瑞利散射,其测量的大气湍流方向与通信卫星方向一致,因此可以有效解决星地激光通信中的提前角问题。实验模拟了1 m口径的地基望远镜作为上行激光发射装置和后向散射光斑成像设备,通过等效高度分别为10 km和17 km的上行激光后向散射光斑图像来实现对10 km以下大气湍流的波前探测。实验采用的波前畸变模拟装置包括空间光调制器和透明塑料片,实验结果表明,对不同的波前畸变PPPP和通用的夏克-哈特曼波前探测器可以实现相似的波前重构,两者重构相位的残差约为初始相位的30%。

热效应作用下S波入射弹性地基自由场地地震响应研究

基于热弹性介质中波的传播理论,建立了平面S波入射下弹性地基自由场地模型,采用亥姆霍兹矢量分解原理,对热效应作用下弹性地基自由场地中的波场进行分析,获得了热效应作用下平面S波入射弹性地基自由场地地震地面运动的解析解答。通过数值计算,分析了热传导系数、介质温度、热膨胀系数等热物性参数对弹性地基自由场地地震地面运动所产生的影响规律。研究结果表明:考虑热效应和不考虑热效应的两种理论模型下所得到的水平和竖向位移放大系数有着明显差异;地表水平和竖向位移放大系数以及相应的加速度随着热膨胀系数和介质温度的增大而增大;热传导系数和热通量相位延迟对地表位移放大系数和加速度的影响较小;随着入射波频率的增大,地表位移放大系数和加速度均逐渐增大。

P波入射下饱和冻土自由场地地震地面运动分析

地震波的放大或衰减受场地条件的影响,因而选择符合实际情况的场地模型来分析地震地面运动极为重要。为了研究西部高寒地区冻土场地的地震地面运动特征,基于弹性波在单相弹性介质与冻结饱和多孔介质中的传播理论,建立了P波入射下基岩上覆饱和冻土自由场地模型,求得了平面P波入射情况下基岩上覆饱和冻土自由场地地震地面运动的解析解答。通过数值计算,分析了平面P波在不同入射角度下,入射频率、孔隙率、介质温度、胶结参数和接触参数等物理力学参数对饱和冻土自由场地地震地面运动的影响规律。分析结果表明:平面P波的入射频率对基岩上覆饱和冻土自由场地地表位移有显著影响。基岩上覆饱和冻土自由场地的水平位移随着平面P波入射频率增大而减小,竖向位移随入射频率增大而增大;孔隙率的增大也会导致饱和冻土自由场地水平位移增大,但其增幅随着平面P波入射角度的增加先增大后减小,竖向位移也增大,但增幅随入射角度增加逐渐减小;冻土场地中介质温度的降低会导致饱和冻土自由场地的水平位移和竖向位移减小。这表明冰相对于冻土场地中地震波传播具有重要影响;此外,泊松比也会对自由场地的位移产生一定影响,水平位移随泊松比增大而减小,增幅随平面P波入射角度增加先增大后减小。随着泊松比增大,饱和冻土自由场地的竖向位移显著增大,增幅随平面P波入射角度增加逐渐减小;接触参数的增加会导致自由场地的水平位移增大,增幅先增大后逐渐减小。同时,地表竖向位移也会增大,但增幅逐渐减小。

基于路侧激光雷达的障碍物目标检测方法

针对现有障碍物检测方法在复杂道路场景下存在地面分割欠精准、计算量大以及不同距离下的目标聚类困难问题,提出了一种基于路侧激光雷达的障碍物检测方法。在地平面分割方面,提出基于圆柱坐标系的改进扇形栅格模型以及最低点代表法优化种子点的选取,采用多地平面模型并通过随机采样一致性算法(RANSAC)实现地面拟合及分割。在障碍物聚类方面,构建KDTree加速聚类过程,提出划分区域及阈值自适应的方式改进欧氏聚类算法。实验结果表明,该方法在4种典型道路场景下对地面点的分割准确率均达到86%以上,且针对不同距离下的障碍物目标聚类准确率提升明显。

In-package P/G planes analysis and optimization based on transmission matrix method

Power integrity (PI) has become a limiting factor for the chip's overall performance, and how to place in-package decoupling capacitors to improve a chip's PI performance has become a hot issue. In this paper, we propose an improved trans- mission matrix method (TMM) for fast decoupling capacitance allocation. An irregular grid partition mechanism is proposed, which helps speed up the impedance computation and complies better with the irregular power/ground (P/G) plane or planes with many vias and decoupling capacitors. Furthermore, we also ameliorate the computation procedure of the impedance matrix whenever decoupling capacitors are inserted or removed at specific ports. With the fast computation of impedance change, in-package decoupling capacitor allocation is done with an efficient change based method in the frequency domain. Experimental results show that our approach can gain about 5× speedup compared with a general TMM, and is efficient in restraining the noise on the P/G plane.

基于地平拟合改进的激光点云滤波算法

针对复杂地形条件下使用传统滤波方法处理激光点云数据时生成的数字高程模型质量较低的问题,提出了一种基于地平拟合和简单形态学(simple morphological filter,SMRF)相结合的点云滤波算法。算法通过SMRF粗滤波生成初始模型,计算原始高程与模型高程差值实现高程归一化;结合渐进移动窗口不断减小的特点,采用地平拟合算法在不同尺寸下构建多个面片集合;利用空间向量后处理,合并过度分割的面片及孤立点,完成地面点云提取。使用ISPRS数据集和实际采集到的点云数据将该算法与4种算法进行比较验证。结果显示,该算法的中误差降低3.3 cm,平均绝对误差降低2.0 cm,与真实地形的相关度达到0.9964,在8组实验区的平均Ⅰ类误差、Ⅱ类误差和总误差分别为2.54%、7.47%和3.06%,滤波精度明显提高。

混凝土防渗面板裂缝综合无损检测技术研究

针对某面板堆石坝混凝土防渗面板表面裂缝,采用地质雷达法、冲击回波法和超声波平测法等无损手段进行检测,分析了不同裂缝的电磁波场响应特征,评估了冲击回波法和超声平测法对不同裂缝的检测效果及影响因素,并进行了误差分析;对比钻孔取芯结果,探讨了基于整体快速探测与局部精准测量相结合的综合无损检测方法在裂缝检测中的有效性和精准度。研究结果表明:地质雷达法直观高效,可实现对防渗面板裂缝的整体检测,快速识别裂缝分布及物性形态;冲击回波法和超声波平测法以其准确灵活的优势,可进一步判定裂缝的深度;通过合理组合检测方法、科学布设测线,综合无损检测方法可查明目标区域裂缝的位置分布、形态规模和具体尺寸,提升裂缝检测的全面性、准确性及精准度。

基于车载激光雷达的稳健地面分割方法

针对在不同场景下车载激光雷达地面分割存在误分割和欠分割的问题,提出了基于多区域稳健平面拟合和多条件约束的地面分割方法。首先构建多区域地面模型,为每个区域分配适当密度的点云。其次在每个区域中构建地面骨架,利用稳健平面拟合估计地面模型,通过置信度传播联合多约束条件去除非地面模型。最后利用平面拟合残差指导边界处的点云分割,进一步提升分割准确性。实验结果表明了,该方法在不同场景下综合评估指标F1能够保持在95%左右,且能适用于不同类型的激光雷达,验证了所提方法具有较强的稳健性和准确性。

导线间距变化对阻抗的影响探讨

主要介绍印制电路板(PCB)中导线间距对阻抗的影响及解决办法,为解决PCB中的阻抗设计及生产存在的问题做理论解析并提供技术支持。