波束锐化技术在多波束测深声呐中的应用

针对常规波束形成器的分辨性能和旁瓣性能间的矛盾,研究了超波束形成器的波束特征以及空间分辨性能。通过计算机仿真验证了加权超波束形成器既有较高的空间分辨力,又有良好的旁瓣特性。通过对外场实验数据的处理,验证了该算法对于多波束测深声呐测量结果中存在的"隧道效应"假象具有明显的抑制作用。针对算法实现结构进行了优化,进一步减小了算法复杂度。利用DSP进行了算法实现,算法具有较好的实时性和工程实用性。     

改进的超波束形成算法探讨及性能研究

为进一步提高超波束形成(Hyper Beam Forming,HBF)算法的性能,在传统的HBF基础上提出一种改进的HBF(Improved Hyper Beam Forming,Im-HBF)算法。将基于半阵指向性函数高阶运算修正到基于全阵指向性函数的高阶运算。仿真结果表明,Im-HBF算法具有更窄的主瓣,并且对端射来波信号栅瓣抑制能力更强,进一步提高了对目标的检测能力。同时,Im-HBF算法对指数n具有更为广泛的适用性,当指数n2时也能获得优于常规波束形成(Conventional Beam forming,CBF)的波束性能。     

一种基于Notch滤波器的恒定束宽波束形成技术

对于存在不同线谱成分的宽带信号而言,提取这些线谱成分进行恒定束宽波束形成,可以达到增强信号的目的。自适应陷波器(Notch滤波器)具有频率跟踪和相位估计的特性,基于此提出了一种自适应恒定束宽波束形成技术。对于基阵接收到的信号,以其各阵元之间的相位差为媒介,在Notch滤波器离线重构相移波束形成中提取"低频慢变化"的相位信息,对其进行补偿,使输出的重构信号具有"高频快变化"的相位信息,以此将不同频段的信号进行恒定束宽波束形成。以舰船辐射噪声为例,通过仿真和实验研究证实了该方法的有效性。     

旁瓣约束方向不变恒定束宽波束自适应综合

将自适应加权方法应用于波束图的主瓣控制研究,提出了方向不变恒定束宽波束形成算法。在波束图旁瓣区域引入若干虚拟干扰源,自适应调整干扰强度,改变波束形状。以主瓣某一指向的波束宽度为参考,以每次迭代后波束图最低旁瓣峰值与主瓣峰值的差作为下次迭代运算的预设主旁瓣比,在保持主瓣区域宽度不变的情况下,用自适应综合的方法获得不同主瓣指向上的最低均匀旁瓣。将该算法应用于均匀线阵和半球面阵,均在±60°的范围内得到了方向不变恒定束宽波束。研究表明,该算法不仅适用于均匀线列阵,也可用于任意结构阵列。     

基于滑动平均的等间隔线阵逆波束形成

逆波束形成算法与常规波束形成相比具有较高的方位分辨力和阵增益,抑制噪声能力强,但其旁瓣却较高,因此采用峰值统计信息作为输出。这样解决了高旁瓣下信号检测的问题,但却丢失了功率谱密度信息。本文在分析逆波束形成算法高旁瓣起因的基础上,提出了用滑动平均抑制旁瓣的方法。仿真分析结果表明,滑动平均方法在保留逆波束形成算法高分辨力的基础上,有效的抑制了旁瓣(第一旁瓣下降了2dB～3dB)。因此,可以采用传统的方法进行输出,以保留功率谱密度信息。海上试验数据的处理结果进一步验证了滑动平均方法的优点。     

全设计频段束宽恒定的低旁瓣时域波束形成

为了在空域无失真地接收宽带信号和有效地抑制环境干扰,提出了全设计频段束宽恒定的低旁瓣时域波束形成方法。首先,把宽带信号分为几个子带,应用半定规划的优化方法设计这些子带中心频率上的加权,使所形成的波束主瓣与设计带宽中最低频率上的波束相同,同时约束其具有低旁瓣特征。然后,设计FIR滤波器拟合这些离散频率点上恒定束宽加权所表示的幅相加权。显然,设计得到的FIR滤波器的幅相响应给出了全设计频段上的幅相加权。最后应用该方法,针对阵元具有方向性的12元均匀离散圆弧阵,设计覆盖一个倍频程的低旁瓣时域恒定束宽波束形成器,并使用线性调频信号作为测试信号,验证了所提方法的有效性。     

超波束处理方法的快速实现及试验验证

提出了超波束处理方法在主动声纳中的快速实现方法。通过对阵元信号进行下变频降采样,并采用阵元信号先匹配滤波再波束形成的步骤,降低了信号处理的计算复杂度,使超波束处理方法易于在实时信号处理系统上实现。使用湖试数据处理结果验证了实现方法的正确性,并对超波束处理方法的性能进行了比较。     

基于协方差矩阵加权的任意阵列宽带恒定束宽波束形成方法

提出了基于协方差矩阵加权方法的恒定束宽波束形成方法,它适用于任意几何形状和阵元方向性的传感器阵列。设计方法为：首先将设计频带分成若干子带,采用优化方法,通过对各子带波束施加约束,设计出具有设定波束形状的各子带波束。然后,对各子带波束进行能量综合,完成宽带信号处理。该方法解决了协方差矩阵加权波束形成方法在宽带系统中会出现的频谱畸变问题．提高了其宽带信号处理性能,为此类的宽带系统设计提供了理论支持。通过计算机仿真和湖试实验数据验证了方法的正确性。     

基于恒定束宽波束输出的宽带相干源高分辨测向

本文给出了基于恒定束宽波束输出的宽带相干源分辨测向方法。计算机仿真表明本方法在降低运算量的同时,得到了优于相干信号子空间方法的方位估计性能。     

潜艇辐射噪声测量方法

潜艇的辐射噪声是反潜战中潜艇平台的致命性指标，本文提出采用多倍频程恒定束宽线列阵波束形成的方法，对潜艇辐射噪声进行宽带测量。     

Deposition of diamond like carbon (DLC) and C-N films using ion beam assisted deposition (IBAD) technique and evaluation of their properties

Diamond like carbon films and C-N films were prepared using ion beam assisted deposition technique (IBAD). Tribological properties were studied by subjecting DLC coated films to the accelerated wear tests. These tests indicated a significant improvement in the mechanical surface properties of glass by DLC coating. Better wear features were obtained for thinner DLC coating as compared to the thicker ones. We also studied the optical properties and obtained a band gap of 1·4 eV for these films. An attempt was made to prepare C₃N₄ films by using IBAD. We observed variation in the nitrogen incorporation in the film with the substrate temperature.     

Metal cluster complex primary ion beam source for secondary ion mass spectrometry (SIMS)

To develop a solution-type ion beam source utilizing a wide variety of metal cluster complexes that are stable only in organic solvents, we have investigated an electrospray method for transferring ions from solutions to gas phase. As initial experiments, we have studied electrospray characteristics of ethanol solutions containing a room-temperature molten salt (i.e., an ionic liquid) and acetic acid as alternatives to solutions of metal cluster complexes. In electrospray experiments, we used a stainless-steel capillary with an inner diameter of 30 μm. Experimental results showed that electrosprayed currents increased with applied voltage in both positive-ion and negative-ion modes. In addition to positive currents, stable negative currents were also confirmed to be produced. Current exceeding 250 nA was produced at 2 kV with a flow rate of 2 μL/min at a concentration of 1 × 10⁻³ mol/L. It was confirmed that several nA out of electrosprayed currents were delivered through an orifice (120 μm internal diameter) into a vacuum chamber. Experimental results indicate that the electrospray method seems to be applicable to an ion beam source for utilizing massive metal cluster complexes in solutions.     

Epitaxial growth of CoFe2O4 on SrTiO3 (100) and MgO (100) substrates without buffer layer by laser molecular beam epitaxy technique

Among the family of ferrite materials, cobalt ferrite (CoFe₂O₄) is unique in that it has the highest values of magneto-crystalline anisotropy and magnetostriction. Recently, much of the efforts have been focused on the fabrication of single crystalline cobalt ferrite films. For the epitaxial growth of cobalt ferrite, the issues of lattice parameter and crystal symmetry mismatch with the substrate are of considerable importance. The growth of thin films of CoFe₂O₄ on MgO and SrTiO₃ single crystal substrates is reported in this paper. The key parameters on the growth modes were investigated by changing oxygen pressure and substrate temperature. Results show that the two-dimensional layer-by-layer growth mode only occurs under high oxygen pressure for epitaxy of Co ferrite. The significant observation presents the controllable lattice constant of a highly strained thin film by modulation of the substrate temperature. In this light, to grow high quality Co ferrite thin films on SrTiO₃ is of a considerable importance to modulate intrinsic magnetic properties.     

Electron beam irradiated HDPE/EVA/Mg(OH)2 composites for flame-retardant electric cables

The mechanical properties and flammability of high-density polyethylene (HDPE)/ethylene vinyl acetate (EVA) mixed with various amounts of magnesium hydroxide (Mg(OH)₂) as the filler in composites, irradiated with electron beam at an irradiation dose of 150 kGy, have been studied. It is found that high-energy electron beam irradiation has significant effects on the mechanical properties of the HDPE/EVA/Mg(OH)₂ composites. The tensile strength and elastic modulus increased greater than in the unirradiated ones. Meanwhile, with increasing the content of Mg(OH)₂ in the composites, the limiting oxygen index (LOI) value increased sharply. The microstructure of the caves of the unirradiated HDPE/EVA/Mg(OH)₂ composites show poor interface of composites compared with the irradiated ones, as observed in SEM micrographs.     

Gas-source molecular beam epitaxy of Si(111) on Si(110) substrates by insertion of 3C-SiC(111) interlayer for hybrid orientation technology

A method to realize a novel hybrid orientations of Si surfaces, Si(111) on Si(110), has been developed by use of a Si(111)/3C-SiC(111)/Si(110) trilayer structure. This technology allows us to use the Si(111) portion for the n-type and the Si(110) portion for the p-type channels, providing a solution to the current drive imbalance between the two channels confronted in Si(100)-based complementary metal oxide semiconductor (CMOS) technology. The central idea is to use a rotated heteroepitaxy of 3C-SiC(111) on Si(110) substrate, which occurs when a 3C-SiC film is grown under certain growth conditions. Monomethylsilane (SiH₃-CH₃) gas-source molecular beam epitaxy (GSMBE) is used for this 3C-SiC interlayer formation while disilane (Si₂H₆) is used for the top Si(111) layer formation. Though the film quality of the Si epilayer leaves a lot of room for betterment, the present results may suffice to prove its potential as a new technology to be used in the next generation CMOS devices.     

Proposal for an advanced hybrid K-edge/XRF densitometry (HKED) using a monochromatic photon beam from laser Compton scattering

The general purpose Monte Carlo electron-gamma shower computer code (EGS5) was used to obtain the U, Np, and Pu X-ray response from the hybrid K-edge/XRF densitometry (HKED). In the present simulation, we adopt a monochromatic, linearly polarized photon beam generated by using inverse Compton scattering of laser light with high-energy electrons from an energy recovery linac. The simulation has been carried out under various conditions of the U, Np, and Pu concentrations to investigate the effect of counting rates as well as counting precision. The results of the simulation show that the assessment time for low concentration Pu input solutions is reduced by improving the signal-to-background ratios. It is also shown that the Np concentration is determined with the counting precision of 0.67-1.8% in standard deviation during 1 h live time measurement for a 3N HNO₃ sample solution (1.1-1.3 g/cm²) including U (10-200 g/L), Np (0.1 g/L), and Pu (10 g/L).     

Secondary‐Emission signal for weld formation monitoring and control in eletron beam welding (EBW)

The process of emission of term electrons from the zone of effect of the electron beam are analyzed. During the experiments, the samples of stainless steel and titanium alloy were welded. Experiments were conducted to examine the spectrum of oscillations of the secondary current at various values of the specific power of the electron beam. The conducted research showed that the signal spectrum of the secondary current in electron beam welding contains a characteristic high‐frequency (15…?25 kHz) component. It was established that the described frequency spectrum is not created by some control system in the electron beam machine and reflects the oscillations in the system – «keyhole‐plasma». Empirical density distribution of the high‐frequency signal was constructed in the amplitude range. It was shown that the parameters of the density distribution is closely linked with the nature of interaction between the beam with the metal and can be used for remote control of technology process.