Ultra-thin single-layer transparent geometrical phase gradient metasurface and its application to high-gain circularly-polarized lens antenna

A new method to design an ultra-thin high-gain circularly-polarized antenna system with high efficiency is proposed based on the geometrical phase gradient metasurface（GPGM）.With an accuracy control of the transmission phase and also the high transmission amplitude,the GPGM is capable of manipulating an electromagnetic wave arbitrarily.A focusing transmission lens working at Ku band is well optimized with the F /D of 0.32.A good focusing effect is demonstrated clearly by theoretical calculation and electromagnetic simulation.For further application,an ultra-thin single-layer transmissive lens antenna based on the proposed focusing metasurface operating at 13 GHz is implemented and launched by an original patch antenna from the perspective of high integration,simple structure,and low cost.Numerical and experimental results coincide well,indicating the advantages of the antenna system,such as a high gain of 17.6 d B,the axis ratio better than 2 d B,a high aperture efficiency of 41%,and also a simple fabrication process based on the convenient print circuit board technology.The good performance of the proposed antenna indicates promising applications in portable communication systems.

Optical spiral vortex from azimuthally increasing/decreasing exponential phase gradients

A new type of power-exponent-phase vortex-like beams with both quadratic and cubic azimuthal phase gradients is investigated in this work.The intensity and orbital angular momentum(OAM)density distributions are noticeably different when the phase gradient increases or decreases along the azimuth angle,while the orthogonality and total OAM remain constant.The characteristics of the optical field undergo a significant change when the phase shifts from linear to nonlinear,with the variation of the power index having little impact on the beam characteristics under nonlinear phase conditions.These characteristics provide new ideas for applications such as particle manipulation,optical communications,and OAM encryption.

IMPROVEMENT OF PHASE GRADIENT AUTOFOCUS ALGORITHM

The phase error estimated by phase gradient autofocus(PGA) is not based on a finite order polynomial mode, so PGA has a good autofocus property for arbitrary order phase error and is fit for high resolution airborne SAR. But PGA has two shortcomings: first, it has a worse estimation property for fast changing phase error; second, there exists a section of linear phase in the phase error estimated by this algorithm. This paper introduces the idea of rank one phase estimate (ROPE) autofocus technique, and improves PGA. The improved PGA(IPGA) can successfully overcome both these shortcomings of PGA.

Effects of temperature gradient on the interface microstructure and diffusion of diffusion couples:Phase-field simulation

The temporal interface microstructures and diffusions in the diffusion couples with the mutual interactions of the temperature gradient, concentration difference and initial aging time of the alloys are studied by phase-field simulation, and the diffusion couples are produced by the initial aged spinodal alloys with different compositions. Temporal composition evolution and volume fraction of the separated phase indicate the element diffusion direction through the interface under the temperature gradient. The increased temperature gradient induces a wide single-phase region on two sides of the interface.The uphill diffusion proceeds through the interface, no matter whether the diffusion direction is up or down with respect to the temperature gradient. For an alloy with short initial aging time, phase transformation accompanying the interdiffusion results in the straight interface with the single-phase regions on both sides. Compared with the temperature gradient,composition difference of diffusion couple and initial aging time of the alloy show greater effects on diffusion and interface microstructure.

Phase-only pattern synthesis based on gradient-descent optimization

By applying phase-only technique in array antenna pattern synthesis, antenna arrays can form desired patterns with the use of phase shifters only. A novel phase-only pattern synthesis algorithm is proposed for the passive phased array seeker. This algorithm synthesizes the main beam of the antenna pattern through least-squares approximation, thus minimizing the errors between the actual and the desired main beams. The synthesis problem can be solved by applying gradient-descent optimization. The item for suppressing side lobes is added to the above synthesis problem. To obtain a side lobe level as low as possible, the algorithm assigns different weights to different directions in the side lobe region. The algorithm is run repeatedly and the weights are adjusted adaptively according to the normalized power in the side lobe directions. Detailed examples are presented to demonstrate the accuracy and effectiveness of the proposed approach.

水下声学超表面异常折射方向调控研究

针对波束调控的问题,本文提出了一种控制波前相位的声学超表面。本文依据广义斯奈尔定律,利用不同声速的均匀介质构建了水中多频声学超表面模型,给出声学超表面产生异常声折射的基本原理,验证了声学超表面在多个频点下可以实现异常声折射现象,揭示了频率以及声波入射角对声学超表面异常折射现象的影响规律,制备了声学超表面实物在水箱中对理论结果进行验证。结果表明:在入射波频率为基频的整数倍时,超表面模型可以实现折射角相同的异常折射现象,并且入射角在一定范围内可以实现负折射现象。实验测量了水中钢板和超表面的折射情况,相较于均匀介质,在不同入射角度下设计的超表面均可以实现异常折射,并且测量值与理论值吻合较好。

A Spectral Projected Gradient-Newton Two Phase Method for Constrained Nonlinear Equations

In this paper, we proposed a spectral gradient-Newton two phase method for constrained semismooth equations. In the first stage, we use the spectral projected gradient to obtain the global convergence of the algorithm, and then use the final point in the first stage as a new initial point to turn to a projected semismooth asymptotically newton method for fast convergence.

稠油油藏体相流体非线性渗流理论模型

根据稠油油藏体相流体渗流特点,建立基于稠油吸附边界层和屈服特性影响下的稠油体相流体非线性渗流理论模型及启动压力梯度理论公式,并利用岩心渗流与启动压力梯度试验结果对理论模型计算结果进行验证。结果表明:理论计算结果与试验结果拟合较好,启动压力梯度理论公式计算结果平均偏差为7.77%,稠油油藏体相流体非线性渗流理论模型计算结果平均偏差为7.50%,均在可接受偏差范围内,并且该模型针对不同流变类型的流体渗流都具有较好的普适性。

基于波动应力信息的隧道地质三维超前探测技术

在隧道施工过程中,地质超前预报技术是必要手段和工序,也是制约隧道施工技术发展的关键技术难题。地震波法隧道超前地质预报施作是一个力学过程。本文将隧道围岩假设为固、气(孔隙)双相介质,在Biot波动理论的基础上,通过分析人工地震波引起的围岩应力应变关系,结合反射面处的地震波入射、折射、透射连续方程及波阻抗与反射系数关系,得到了围岩广义应力梯度与地震波瞬时振幅与瞬时频率之间的关系表达式,并建立了围岩应力信息与地质信息的联系。在此基础上,将隧道围岩广义应力梯度作为评价地质灾害的重要指标,形成了基于围岩应力信息的地震波超前地质预报方法,解决了现有预报多解性问题。经过现场试验验证,围岩应力信息能够很好地表达地质岩性变化,结合波速和走时,可以准确判定地质灾害规模、类型及位置。

考虑相含量的TC17钛合金线性摩擦焊中的残余应力

为了获得准确的TC17钛合金线性摩擦焊中的残余应力,建立TC17钛合金弹性常数与相分数之间的数值关系。结合焊接区域的相分数,获得呈梯度分布的弹性常数,并将其引入轮廓法进行计算。结果表明,TC17钛合金的弹性常数与α相分数呈正相关,在宽度约4 mm的焊接区域呈现明显的梯度分布特征;若忽略相分数的梯度分布,计算残余应力时相对误差可达36.06%;修正后的残余应力呈双峰分布,在热影响区边缘处达到峰值,约为442 MPa。这说明考虑相分数的梯度分布是必要的。

基于贝叶斯神经网络的相位梯度计算方法

应变重构是相衬光学相干层析力学性能表征中的关键步骤,其需要准确计算出差分包裹相位的梯度分布。为了能够解决强噪声干扰下的相位梯度重构信噪比低的难题,提出了一种基于贝叶斯神经网络的相位梯度计算方法。首先,通过计算机模拟不同散斑噪声等级下的包裹相位图,并生成相应的理想相位梯度,以构建网络的训练集。其次,基于网络训练集采用贝叶斯推断理论学习强噪声环境下的包裹相位与相位梯度的“端到端”映射关系。最后,将相衬光学相干层析测量的差分包裹相位结果送入贝叶斯神经网络进行处理,实现高信噪比相位梯度预测。此外,通过借助贝叶斯神经网络的统计特性,以模型不确定度来定量评估相位梯度预测结果的可靠性。通过数值实验和三点弯曲力学加载实验对比分析了本文方法和主流矢量方法的性能。实验结果表明:在噪声较小的条件下,本文方法重构的相位梯度信噪比可提升8%;在噪声较强条件下,本文方法能成功恢复因相位条纹难以分辨而无法计算的相位梯度。此外,模型不确定度能够定量分析网络的相位梯度预测误差。可以预见,在样品形变复杂且先验信息未知的条件下,本工作为相衬光学相干层析提供了一种有效的应变重构方法,从而能实现高质量和高可靠的内部力学性能表征。

基于GBDT的气液两相流相分布测量模型

双波长透射法是一种高精度的多相流相分布参数检测方法,为了进一步提高相分布测量的精度,本文提出用梯度提升决策树(GBDT)算法建立相分布测量模型。利用光学仿真,模拟气泡在不同相分布下波长为445nm和635nm的光线在气液两相流中的传播过程,采集检测平面的光强分布,分析不同相分布情况下气泡中心位置和气泡半径对光强分布曲线的影响;用GBDT建立测量模型,以光强缺失宽度和缺失偏移为特征参数,建立特征参数与气泡相分布之间的对应数据库,利用数据库对GBDT模型进行训练;用训练好的模型预测气泡的相分布。建立的测量模型对气泡相分布预测的均方误差小于0.0008mm,均方误差减小了33.33%,证明了测量模型更适用于相分布的测量。搭建了实验平台,对竖直上升气泡流相分布参数进行预测,实现了对气泡中心位置运动轨迹的追踪。

波前编码红外成像系统的温度梯度适应能力探究

利用波前编码技术为红外光学系统进行无热化设计可提高其在不同均匀工作温度下的适应能力,但针对温度突变、成像系统内温度分布不均情况,波前编码技术是否能正常进行成像及其适用的温度范围还有待进一步研究.为简化分析流程,采用温度梯度模型来仿真非稳态下的温度变化.利用温度梯度模型来定性分析光学系统在轴向、径向温度梯度为系统引入的附加像差.计算两个方向下的光程差变化来比较两种温度梯度环境下系统的成像性能差异.在此基础上,为非稳态温度环境下红外光学系统的设计建立了结合光/机/热分析的无热化设计流程,通过ZEMAX设计了一套最大轴向尺寸为85 mm、最大径向尺寸为25 mm的红外光学系统,通过SolidWorks加载轴向和径向的热形变,探究所设计的系统能够适用的温度梯度范围.结果表明,结合光/机/热分析的无热化设计流程可以有效表明系统在非稳态温度下的成像情况.对上述采用三次相位板进行无热化设计的红外光学系统,在非稳态温度下可以适应±10℃的轴向温差范围,但是仅可以适应±1℃的径向温差范围.因此在进行红外波前编码光学系统的无热化设计时,需要对径向方向进行重点优化.

提高植入式电子设备无线充电效率的技术研究

为解决植入式电子医疗器械在无线能量传输(Wireless Power Transmission, WPT)时效率较低的问题,根据Pancharatnam-Barry理论设计了一种可穿戴超表面结构,利用梯度相位设计调整电磁波入射角度,使波矢量方向尽可能垂直于皮肤,从而提高体内受电单元的能量接收功率。这种超表面单元具有良好的极化转换效率,透射幅度达到0.8以上。为验证其合理性,搭建人体局部等效模型进行系统仿真,结果表明加入超表面后系统的传输系数提高了5 dB,并且人体内的电场强度分布也明显改善,植入天线工作区域的场强显著提高,所设计结构有效改善了植入系统的能量传输效率(Power Transfer Efficiency, PTE)。实验结果进一步验证了该设计的有效性,所提出的超表面结构具有柔性、高效和易集成等优点,为提高植入系统无线PTE提供了一种有效的解决方案。

Enhanced multi-baseline unscented Kalman filtering phase unwrapping algorithm

This paper presents an enhanced multi-baseline phase unwrapping algorithm by combining an unscented Kalman filter with an enhanced joint phase gradient estimator based on the amended matrix pencil model, and an optimal path-following strategy based on phase quality estimate function. The enhanced joint phase gradient estimator can accurately and effectively extract the phase gradient information of wrapped pixels from noisy interferograms, which greatly increases the performances of the proposed method. The optimal path-following strategy ensures that the proposed algorithm simultaneously performs noise suppression and phase unwrapping along the pixels with high-reliance to the pixels with low-reliance. Accordingly, the proposed algorithm can be predicted to obtain better results, with respect to some other algorithms, as will be demonstrated by the results obtained from synthetic data.

激光相干合成系统中SPGD算法的分阶段自适应优化

为改善传统随机并行梯度下降(Stochastic Parallel Gradient Descent,SPGD)算法应用于大规模激光相干合成系统时收敛速度慢且易陷入局部最优解的情况,提出了一种分阶段自适应增益SPGD算法-Staged SPGD算法。该算法根据性能评价函数值,在不同收敛时期采用不同策略对增益系数进行自适应调整,同时引入含梯度更新因子的控制电压更新策略,在加快收敛速度的同时减少算法陷入局部极值的概率。实验结果表明:在19路激光相干合成系统中,与传统SPGD算法相比,Staged SPGD算法的收敛速度提升了36.84%,针对不同频率和幅度的相位噪声,算法也具有较优的收敛效果,且稳定性得到显著提升。此外,将Staged SPGD算法直接应用于37、61、91路相干合成系统时,Staged SPGD算法相比传统SPGD算法收敛速度分别提升了37.88%、40.85%和41.10%,提升效果随相干合成单元数增加而更加显著,表明该算法在收敛速度、稳定性和扩展性方面均具有一定优势,具备扩展到大规模相干合成系统的潜力。

一种改进选点及加窗处理的相位梯度自聚焦算法

相位梯度自聚焦(Phase Gradient Autofocus,PGA)算法被广泛应用于补偿合成孔径雷达(Synthetic Aperture Radar,SAR)图像的相位误差。PGA算法的处理流程中,选点和加窗这两步操作对于算法性能的影响非常大。传统的PGA算法常因选点质量不佳或窗宽估计有误而导致聚焦效果变差,收敛速度变慢。本文提出一种基于能量-信杂比最大准则的强点选择方法和一种自适应窗宽估计方法。利用能量和信杂比两个维度从图像数据中筛选出理想的孤立强散射点,结合并改进两种传统加窗方法自适应地估计窗宽,实现算法稳定性和收敛速度的提升。仿真和实测数据处理结果证实了本文算法的有效性。

高含CO_(2)凝析气藏成藏过程中的流体相行为及油环体积预测

成藏后期的CO_(2)充注导致里贝拉区块高含CO_(2)次生凝析气藏的流体相行为十分复杂,油环体积预测难度很大。本文通过流体相平衡模拟、组分梯度分布计算及CO_(2)充注可视化实验,刻画了CO_(2)充注过程中的油气相行为,揭示了油环体积的动态变化规律,建立了基于气顶气组分拟合的高含CO_(2)次生凝析气藏油环体积预测新方法。研究结果表明:1)CO_(2)充注下的油环体积变化分为4个阶段:充注初期,油环以溶胀为主;充注前期,CO_(2)不断置换并萃取油相中的轻质组分,油环体积迅速降低;充注中期,CO_(2)持续萃取油相的轻、中质组分,油环体积缓慢减小;充注后期,CO_(2)-原油组分传质作用明显减弱,压缩效应导致油环体积进一步减小。2)轻质组分的强流动性使气顶气组成均一,重力分异作用使纵向上油环组分呈梯度变化。3)油环体积与气顶气组成和气油比密切相关。4)基于气顶气拟合新方法和不同井深现场勘探预测的油环体积占比分别为19.21%和22.30%,与CO_(2)充注可视化实验获得的油环体积占比(20.60%)较为吻合。

岩心油水两相渗流启动压力梯度实验研究

低渗储层油水两相渗流时存在启动压力梯度,充分认清水驱油时启动压力梯度的变化和影响因素对油藏水驱开发至关重要。为了搞清油藏储层油水两相渗流启动压力梯度特点及其影响因素,对不同渗透率、不同含水饱和度、不同润湿性岩心水驱油两相渗流的启动压力梯度进行了室内实验测定,根据实验现象和实验结果,分析了产生启动压力的岩心孔隙内部的阻力效应和微观成因。研究结果表明:气体渗透率小于50×10^(-3)μm^(2)的低渗岩心随含水饱和度增加,启动压力梯度增大;气体渗透率大于50×10^(-3)μm^(2)的中高渗岩心启动压力梯度随含水饱和度变化不大,总体呈下降趋势,且数值较小;对于低渗油藏,启动压力梯度随岩心渗透率降低而增大,随岩心润湿指数增加而减小;岩心边界层液体厚度越大,启动压力梯度越大。产生启动压力的附加阻力效应有油滴毛管力产生的摩擦阻力、静润湿滞后导致油珠变形产生的阻力及液阻效应产生的阻力,其大小和岩石孔喉半径、润湿指数、微观孔隙的油水分布状态、边界层厚度及固液界面张力有关。

Modified Approach to PGA Phase Averaging for ISAR Autofocus

A new approach to phase averaging in phase gradient algorithm (PGA) is proposed, which is based on the fundamental fact that the information of translational phase error is widely contained in every defocused scatterer in ISAR image. The new approach aims to choose strong scatterers for error phase averaging with a threshold rather than just simply to pick out the strongest point in each range cell, which is not necessarily real strong scatterers if in some range cells consists more than one strong scatterer and whereas in other range cells no scatterer at all. The results of processing real data are presented to confirm the validity of the proposed approach.