任意几何形状和阵元指向性的传感器阵列优化波束形成方法

针对常规波束运用到实际传感器阵列时旁瓣较高这一缺点,提出了适用于任意几何形状和阵元指向性的传感器阵列的两种旁瓣约束优化波束形成方法。一种是主瓣宽度约束条件下的最低旁瓣波束形成,另一种是在所能允许的最高旁瓣约束条件下的高增益波束形成。通过对加权向量范数进行约束,提高波束形成的稳健性。这两种优化波束形成问题都可以写成二阶锥(Second-OrderCone)约束优化的形式,然后利用已有的内点方法(Interior-PointMethods)求出其数值解。计算机仿真和湖上实验数据处理结果表明,该低旁瓣波束形成方法相比于常规波束和其它基于自适应波束形成的旁瓣控制方法,在同等主瓣宽度的情况下可以获得更低的旁瓣级;该高增益波束形成方法在同等旁瓣级约束条件下可以获得更高的阵增益,而且旁瓣级能够满足设定要求。     

Plasmonic sensor with variable claddings based on metallic slit arrays

We propose a plasmonic sensor with variable refractive index(RI), which exhibits high sensitivity and extraordinary optical transmission(EOT). Its variable RI is attributed to its dielectric layers and metallic slit arrays.According to simulation results, the third resonant wavelength has a wavelength sensitivity of 800 nm/RIU and an ultra-high transmittance of 0.8 by adjusting the RIs of the upper and lower dielectrics, incident light angle,and structural geometric parameters. With its unique features, the proposed structure holds considerable potential for extensive application to metal–dielectric grating sensors operating at visible and near-infrared frequencies.     

Approximately linear relations between two-nucleon and three-nucleon parameters

The correlation between the triton binding energyE _t and then-d scattering length² a and the zero energy singlet and triplet wound integral I_os and I_ot is investigated, with phaseequivalent separableNN interactions obeying all the important off-shell constraints. It is found that the correlation betweenE _t and² a is stronger than betweenE _t (² a) andI _os ,I _ot separately. A strong correlation is also found between the percentageD-state in the deuteronP _d andI _ot . Fixing all the other off-shell parameters but allowing variations ofI _os andI _ot leads to surprisingly accurate linear relations betweenE _t(² a) andI _os ,I _ot (P _d). These relations depend strongly on the other off-shell parameters.     

Fabrication of gas ionization sensor based on titanium oxide nanotube arrays

Gas sensors have been fabricated based on field ionization from titanium oxide nanotubes grown on titanium foil. Ordered nanaotube arrays of titanium oxides were grown by the anodization method. We measured breakdown voltages and discharge currents of the device for various gases. Our gas ionization sensors (GIS) presented good sensitivity, selectivity, and short response time. The GISs based on TiO₂ nanotube arrays showed lower breakdown voltage, higher discharge current, and good selectivity. An excellent response observed for Ar compared to other gases. Besides, by introducing 2 % CO and 4 % H₂ to N₂ flow gas, the amount of breakdown voltage shifts about 20 and 70 volts to the lower values, respectively. The GIS works at room temperature and has the ability of detect inert gases with high stability and good linearity. Besides, short response time of about 1 second for the GISs based on TiO₂ nanotube arrays makes them excellent for gas sensing applications. Sharp edges of the nanotubes, through enhancing the applied electric field, reduce operating voltage to the reasonable values and power consumption.     

基于遗传算法的二维随机型稀疏阵列的优化研究

为了解决二维相控阵列及与之匹配的三维超声成像系统过于复杂的问题,提出了一种基于遗传算法的随机型稀疏阵列的优化设计方法。在这种方法中,首先根据横向分辨率的要求确定参考阵列的尺寸及加权分布,然后根据对比分辨率的要求确定稀疏阵列相对于参考阵列的稀疏率,最后利用遗传算法优化确定阵元的分布形式。通过连续波理论和基于空间冲激响应的脉冲场模型对这种稀疏阵列的声学特性进行了分析,分析结果表明,优化设计的随机型稀疏阵列具有良好的特性,它与参考阵列有几乎相等的主瓣宽度,而且不产生栅瓣,虽然其旁瓣高度与参考阵列相比略有提升,但经遗传算法优化后仍能满足高质量成像的要求。     

Multiplexing technology based on SQUID for readout of superconducting transition-edge sensor arrays

Multiplexing technologies based on superconducting quantum interference devices (SQUIDs) are crucial to cryogenic readout of superconducting transition-edge sensor (TES) arrays. Demands for large-scale TES arrays promote the development of multiplexing technologies towards large multiplexing factors and low readout noise. The development of multiplexing technologies also facilitates new applications of TES arrays in a wide range of frequencies. Here we summarize different types of SQUID-based multiplexing technologies including time-division multiplexing, code-division multiplexing, frequency-division multiplexing and microwave SQUID multiplexing. The advances and parameter constraints of each multiplexing technology are also discussed.     

Active noise control with linear control source and sensor arrays for a noise barrier

A study is conducted on minimizing the sum of the squared acoustic pressures with a linear array of control sources and a perpendicular linear array of error sensors, placed above the top of a noise barrier. Particular angular orientations, with respect to the center of the barrier top, and spacings of the linear arrays of control sources and error sensors result in moderate to significant additional reduction of the acoustic pressure in the shadow zone. Visual inspection of the sound pressure field, with and without active noise control, found that uniform and significant additional insertion loss can be generated near the barrier. Numerical simulations were conducted to test the proposed method. For separations between control sources and error sensors much less than a quarter wavelength of the primary noise disturbance, results show that the angular orientation, of the combined linear control source and sensor arrays, is a weak factor for acoustic pressure reduction in the shadow zone. Weak angle dependence serves as an advantage to the proposed method, which yields uniform performance for any angular orientation. An angular orientation involving the alignment of the furthest error sensor with the first diffracting edge of the barrier and the primary source was observed to perform well for a variety of frequencies, since the spacing between error sensors and between control sources is of the order of a quarter-wavelength. Improved noise control in the shadow zone of a barrier is achieved by the use of two control sources and angular orientation as mentioned above. Further spatial extension of the area of reduced acoustic pressure is possible by utilizing an increased number of control sources.     

基于宽波束磁电偶极子天线的宽角扫描线性相控阵列

设计并加工了两款基于宽波束磁电偶极子天线单元的宽角扫描线性阵列.首先,通过加载磁偶极子的方法拓展了天线单元的3-dB波束宽度.然后,基于该宽波束天线单元设计了两款具有良好宽角扫描特性的一维阵列天线.实测结果表明,天线单元的E面方向图3-dB波束宽度在9GHz—12 GHz均大于107°,H面方向图3-dB波束宽度在7GHz—12 GHz均大于178°.E面阵列中心单元的有源驻波比在9GHz—13 GHz小于2,相对阻抗带宽为36.36%.H面阵列中心单元的有源驻波比在9.6GHz—12.6 GHz小于2.5,相对阻抗带宽为27.03%.E面阵列在9GHz—12 GHz可实现±70°的有效宽角扫描.H面阵列在9GHz—GHz可实现±90°的有效宽角扫描.与传统的扫描阵列相比,设计的阵列可实现有效宽带宽角扫描,在X波段相控阵雷达方面具有广阔的应用前景.     

Structural transitions in granular packs: statistical mechanics and statistical geometry investigations

We investigate equal spheres packings generated from several experiments and from a large number of different numerical simulations. The structural organization of these disordered packings is studied in terms of the network of common neighbours. This geometrical analysis reveals sharp changes in the network’s clustering occurring at the packing fractions (fraction of volume occupied by the spheres respect to the total volume, ρ) corresponding to the so called Random Loose Packing limit (RLP, ρ ～ 0.555) and Random Close Packing limit (RCP, ρ ～ 0.645). At these packing fractions we also observe abrupt changes in the fluctuations of the portion of free volume around each sphere. We analyze such fluctuations by means of a statistical mechanics approach and we show that these anomalies are associated to sharp variations in a generalized thermodynamical variable which is the analogous for these a-thermal systems to the specific heat in thermal systems.     

Stereo vision sensor calibration based on random spatial points given by CMM

This paper presents a new, high-precision calibration method for stereo vision sensor based on virtual template. Given 3D spatial points coordinates by coordinates measurement machine (CMM) and corresponding image points coordinates, the technique is realized by taking the projection matrix elements as unknown and using singular value decomposition to solve the least-squares solutions. The method avoids solving intrinsic and extrinsic parameters of each camera and introducing the calibration error which caused by template machining and measurement error. We measure the 3D coordinates of a group of random spatial points by the calibrated stereo vision sensor then compare the results with CMM measurement values, the errors are less than 0.05 mm in the Z axis direction, and less than 0.01 mm in the X and Y axis direction, the experiment results show that the technique is feasible and effective.     

基于图像识别技术的随机线缆束建模及分布参数统计分析

提出了一种对实际弯曲随机捆扎线束的建模方法,该方法首先基于图像识别技术,使用实际线束在侧视和俯视方向的两幅照片来实现弯曲线束轴心三维坐标的重建,然后再基于随机转移路径方法实现弯曲线束的捆扎随机性。基于该建模方法,通过蒙特卡洛模拟来分析弯曲随机线束分布参数的统计特征,发现自电感、互电感和互电容均值沿线变化趋势与线束高度变化趋势一致,自电容均值则趋势相反;自电容、自电感和互电感的变异系数与线束高度存在负相关特征;捆扎随机性不会改变自电感和自电容均值,但是会降低互电容与互电感均值。     

Propagation of electrons in linear atomic arrays

In this paper a new approach to the problem of electron propagation in one-dimensional arrays is developed. The approach is based on the concept of reflectance defined in the paper and propagation or non-propagation is determined by the single question of the reflectances being unity or not. This notion throws fresh insight into the localized state in one-dimensional systems and here the notion that all electrons in one-dimensional systems are localized is discussed.     

Critical disorder and phase transitions in random diode arrays

Random diode arrays represent a new class of nonlinear disordered systems related to the physics of thin-film semiconductor structures and some others. When a disorder strength grows through a certain critical value, they undergo a phase transition from almost uniform to strongly nonuniform random electric potential. A piecewise continuous topography of random potential is predicted.     

Double image encryption based on linear blend operation and random phase encoding in fractional Fourier domain

A novel method for double image encryption is proposed by using linear blend operation and double-random phase encoding (DRPE) in the fractional Fourier domain. In the linear blend operation, a random orthogonal matrix is defined to linearly recombined pixel values of two original images. The resultant blended images are employed to constitute a complex-valued image, which is encrypted into an encrypted image with stationary white distribution by the DRPE in the fractional Fourier domain. The primitive images can be exactly recovered by applying correct keys with fractional orders, random phase masks and random angle function that is used in linear blend operation. Numerical simulations demonstrate that the proposed scheme has considerably high security level and certain robustness against data loss and noise disturbance.     

Symmetric patterns in linear arrays of coupled cells

In this note we show how to find patterned solutions in linear arrays of coupled cells. The solutions are found by embedding the system in a circular array with twice the number of cells. The individual cells have a unique steady state, so that the patterned solutions represent a discrete analog of Turing structures in continuous media. We then use the symmetry of the circular array (and bifurcation from an invariant equilibrium) to identify symmetric solutions of the circular array that restrict to solutions of the original linear array. We apply these abstract results to a system of coupled Brusselators to prove that patterned solutions exist. In addition, we show, in certain instances, that these patterned solutions can be found by numerical integration and hence are presumably asymptotically stable.