一种基于长基线交汇的超短基线定位系统精度评价方法

超短基线定位系统的定位精度和准确度是评价系统性能的重要指标, 通常采用固定点的定位重复度来评价定位精度, 采用其他解算方法作为真值参考评价定位准确度. 本文首先分析了以误差椭圆理论为基础的超短基线精度评价方法, 给出了理论推导公式, 证明了观测数据和理论误差椭圆的关系. 本文提出了一种基于长基线交汇的超短基线定位系统精度评价方法, 通过长基线交汇模型求解目标的真实位置评价系统的准确度. 根据该方法解算得到的待定目标位置作为真值参考, 能够反应系统误差的修正情况. 最后采用该方法进行海试数据处理, 处理结果表明该方法能够较好的反应定位精度, 进一步修正了系统偏差, 修正系统偏差后和修正前相比定位精度提高了0.2%, 具有良好的工程应用价值.     

移动平台超短基线阵实现水下目标高精度定位

针对自主式水下航行器如AUV (Autonomous Underwater Vehicle)等水下移动平台,提出了一种超短基线多元阵的快速收敛的高精度声定位方法。通过对比超短基线多元阵定位误差的克拉美罗下界,对阵型结构和阵元数目进行了优化,确定优化的阵列为9元立方阵;融合移动平台行进过程中的多次定位结果,进一步降低定位误差;并利用梯度下降法实现平台轨迹优化,使得系统最快收敛到需要的定位精度。仿真结果表明,在1000 m距离内,利用优化轨迹可以将定位均方根误差快速收敛至预设的0.2%以内.此外,对于海试实验采集数据的目标定位结果显示,对距基阵约700 m及400 m的目标,5元阵定位标准差相较4元阵缩小了约2 m及1 m,验证了多元阵定位方法在实际海洋环境中的有效性.      

双曲面定位系统的误差分析

本文导出了双曲面定位系统的定位误差公式,分析了定位误差源及对应的权重系数,以水下短基线阵为例,计算了声速、时间差、阵元坐标的测量误差和声线弯曲引起的系统定位误差,以长基线阵为例,计算了定位精度区。本文结果对合理分配双曲面定位系统各误差源的误差有参考价值.     

一种稳健的柔性阵波束形成方法

由于航向、航速的改变以及水流、风浪等因素的影响,柔性线列阵在实际应用过程中阵型畸变是不可避免的。一方面,这种畸变使得许多假设阵型无畸变的波束形成方法的性能受到严重的影响;另一方面,目前很多的阵型估计方法仍不是很成熟,很难准确估计阵元的实际位置。本文提出将柔性阵列分为一段阵元位置已知的子阵和若干段阵元未知的子阵,利用不同子阵接收信号的互相关即可获得所需要的波束形成加权系数,从而在不需要知道阵元确切位置信息的情况下实现目标方法的估计。     

多子阵组合的短基线声学定位系统数据优化方法*

短基线声学定位系统是一种常用的水下声学定位设备,为提高适用性,常采用多阵元接收阵的方式进行水声定位,其工作时将带来冗余的测距数据和定位结果,而部分冗余数据的解算定位结果误差较大（以下简称奇异值）,其代入融合将导致最终定位结果的误差不减反增。为解决该问题,本文分析奇异值特征,提出了基于多子阵组合(Multiple Subarray Combination,以下简写MSC)的短基线声学定位数据优化方法。该方法将空间阵中划分出的各单元子阵进行筛选,对冗余数据进行优化,筛除会引入较大误差的中间数据,进而提高定位精度。计算机仿真及实际测试数据表明：该方法可实现整体声源定位精度的提高。同时与传统定位方法相比可有效减小运算量,提高整体定位系统的性能。     

界面反射对超短基线水声定位系统的影响——“跳象限”现象分析与克服

本文通过界面反射对超短基线水声定位系统的影响进行理论分析和计算机仿真,指出了超短基线水声定位系统中存在“跳象限”现象的物理原因,给出了产生“跳象限”现象的必要条件,并提出了防止“跳象限”的具体措施和软件纠正方法.经湖上试验验证,本文进行的理论分析与实验结果相符,所提出的防止“跳象限”方法切实可行.     

阵元随机均匀分布球面阵列联合噪声源定位方法

基于球面传声器阵列的噪声源定位方法,设计加工了阵元随机均匀分布64元球面传声器阵列,研究了球面近场声全息和球谐函数模态展开聚焦波束形成联合噪声源定位识别方法,对算法的性能进行了仿真分析,并利用球面传声器阵列进行了噪声源的定位识别试验.研究表明,阵元随机均匀分布球面阵列具有全空间稳定的目标定位性能,球面近场声全息对低频近距离声源具有较高的定位精度,球谐函数模态展开聚焦波束形成对高频远距离声源具有较高的定位精度,将两种方法联合进行声源的定位识别,可以在较小孔径的球面阵列和较少阵元的条件下,在宽频带范围内获得对目标声源良好的定位性能.     

超短基线基阵基元相移差的测量

本文针对超短基线定位系统定位精度不高的问题，首先介绍了一种改进阵形的高精度定位算法，然后介绍了如何测量基阵附加相移的方法，并在湖试中，应用了此方法得到的补偿相移值，取得较好的定位效果。     

基于遗传算法的不等间距阵优化方法

阵元数一定情况下,针对不等间距拖线阵高频信号处理存在的空间增益和无栅瓣兼容问题,提出一种基于遗传算法的不等间距拖线阵阵型优化方法。该方法以频带交互下最大旁瓣级最小作为约束因子,通过模拟生物自然进化过程搜索全局最优解,得到优化后的阵元位置。优化后阵型在保证低频信号处理空间增益不变情况下,实现对高频信号高空间增益、无栅瓣处理。计算机仿真结果表明：相比未优化阵型,在高频信号处理方面,优化后阵型在无栅瓣情况下,空间增益提升值近似理论值提升值;在低频信号处理方面,优化后阵型具有相同的空间增益。为实际不等间距拖线阵阵型优化和应用提供了一种思路。     

起降客机噪声源识别的平面阵设计

针对起降客机的噪声源识别,给出了平面多臂对数螺旋阵的设计过程。多臂对数螺旋阵可以在较宽的分析频带内保持较小的主瓣宽度,同时平均旁瓣水平较低,从而具有良好的宽带噪声源识别性能,但其阵型设计中需要考虑的参数较多。本文以ARJ21客机起降过程中的主起落架噪声源识别为例,研究了多臂对数螺旋阵各参数对其噪声源识别性能的影响。所给出的阵列设计流程可以为飞行客机的噪声源识别,尤其是多子阵嵌套的平面阵设计提供参考。     

长基线定位系统高精度阵型标定方法

为解决长基线定位系统传统标定方法中受垂直方向声速变化剧烈而导致的标定精度差、逐个声信标交汇标定效率低、跟踪定位阶段采用不同声信标基准对目标解算不一致的问题,本文提出了一种高精度相对阵型标定方法,通过水下声信标的互测距信息构建观测模型改进了传统标定方式。理论分析表明,采用该方法水平方向上能够获得与测距等量级的标定精度,有效地提高了标定效率,采用不同的声信标基准目标解算结果一致,在深海作业中优势明显。通过浅水试验结果可以看出该方法水平方向上的标定精度能达到和测距等量级的毫米量级精度,和传统标定方法相比提高了一个数量级,在提高标定精度的同时降低了作业复杂度,采用本文的标定结果获得的目标定位结果更接近于GPS输出,具有良好的工程应用价值。      

基于倾斜阵的距离与方位联合估计*

针对阵列倾斜引起的阵不变量方法定位精度下降的问题,该文结合倾斜阵声源定位的三维模型提出一种基于倾斜阵的距离与方位联合估计算法。该算法通过联合自校正方位距离联合估计方法对阵列倾角在声源-接收平面的投影量进行估计和补偿,改善目标距离估计误差的同时,利用匹配出的阵列倾角投影量反向估计目标方位,获得对声源二维位置的估计。通过仿真验证了该算法能够在阵列倾角较小时实现目标方位与距离的联合估计。     

基于组合线阵的近程运动小目标被动定位跟踪

针对水下运动小目标被动探测与定位问题,提出了分段组合子阵联合处理探测方法,各探测子阵采用相互垂直结构布局,克服了单阵方位模糊及无法定位等问题。研究了分段组合子阵的宽带最小方差无畸变失真响应近场聚焦目标定位方法,实现了近程蛙人等水下小目标被动高精度定位。在此基础上,采用卡尔曼滤波算法对目标运动轨迹进行预测估计,将目标定位信息与跟踪轨迹信息进行匹配,实现高背景噪音下的运动小目标的跟踪处理。理论分析及仿真结果表明,分段子阵联合处理能有效对水下运动小目标进行定位和跟踪,海试试验进一步验证了该方法的有效性。     

Loudspeaker line array educational demonstration

This paper presents a physical demonstration of an audio-range line array used to teach interference of multiple sources in a classroom or laboratory exercise setting. Software has been developed that permits real-time control and steering of the array. The graphical interface permits a user to vary the frequency, the angular response by phase shading, and reduce sidelobes through amplitude shading. An inexpensive, eight-element loudspeaker array has been constructed to test the control program. Directivity measurements of this array in an anechoic chamber and in a large classroom are presented. These measurements have good agreement with theoretical directivity predictions, thereby allowing its use as a quantitative learning tool for advanced students as well as a qualitative demonstration of arrays in other settings. Portions of this paper are directed toward educators who may wish to implement a similar demonstration for their advanced undergraduate or graduate level course in acoustics.     

线阵CCD用于实时动态测量技术研究

本文研究的是在连续光条件下线阵ＣＣＤ实时动态测量技术,除了考虑ＣＣＤ像元响应非均匀性、非线性等影响因素外,还应认真考虑采样频率、测量精度、动态范围、快速电路等问题。本文还详细讨论了测量精度和动态范围问题,推导了测量精度公式与动态范围公式。为了减小测量误差和提高被测信号的频率,必须相应减小积分时间。精度公式是进行线阵ＣＣＤ电路设计的基本依据公式。动态范围与频率无关,只与结构参数有关,为了充分利用ＣＣＤ的动态范围,激光功率要可调。     

On the steering of sound energy through a supercritical plate by a near-field transducer array

The ability to direct sound energy through the flexural vibrations of a submerged plate at various angles of incidence using a near-field transducer array is investigated. An alumina bar is placed in front of a one-dimensional, eight-element transducer array, between the array and the water. Operating in a receive mode, data were taken as a function of angle of incidence and compared to data taken without the presence of the alumina bar. The array was also operated in transmit mode and results were compared to corresponding receive mode data, showing that reciprocity holds. Results show that in fact sound energy can be steered through a plate, and that the measurement method used provides a convenient method of measuring the angular dependence of transmission through a plate, including measurements at frequencies above the plate's critical frequency. Experimental results of sound transmission versus angle of incidence of finite sized plates agree qualitatively with theoretical results from an analysis of the transmission through an unbounded flexible partition.     

Theoretical analysis of ion cyclotron range of frequency antenna array for HT-7U

This paper considers the coupling analysis of phased antenna array designed to excite fast wave in the ion cyclotron range of frequency. The coupling of the antenna is calculated in slab geometry. The coupling code based on the variational principle gives the self-consistent current flowing in the antenna, this method has been extended so that it can be applied to a phased antenna array. As an example, this paper analyses the coupling prosperities of a 2 × 2 phased antenna array. It gives the optimum geometry of antenna array. The fields excited at plasma surface are found to more or less correspond to the antenna current phasing.     

A dual-tuned quadrature volume coil with mixed λ/2 and λ/4 microstrip resonators for multinuclear MRSI at 7 T

In this work, an eight-element by eight-element dual-tuned quadrature volume coil with a mix of capacitor terminated half-wavelength (λ/2) and quarter-wavelength (λ/4) microstrip resonators is proposed for multinuclear magnetic resonance imaging/spectroscopy studies at 7 T. In the proton channel, λ/2 microstrip resonators with capacitive terminations on both ends are employed for operation at higher frequency of 298.1 MHz; in the heteronucleus channel, capacitor-terminated λ/4 resonators, suitable for low frequency operations, are used to meet the low frequency requirement. This mixed structure design is particularly advantageous for high field heteronuclei magnetic resonance applications with large difference in Larmor frequency of the nuclei in question. The proposed design method makes it much easier to perform frequency tuning for heteronucleus channel using a variable capacitor with a practical capacitance range. As an example, a dual-tuned volume coil for (1)H/(13)C mouse spectroscopic imaging was proposed to demonstrate the feasibility of this method. The finite-difference time-domain method is first used to model this dual-tuned volume coil and calculate the B(1) field distributions at two frequencies. Transmission parameters (S(21)) measured between the proton channel and the carbon channel are -50 dB at 75 MHz and -35 dB at 298 MHz, showing the excellent isolation between the two channels at 7 T. The proton image and (13)C FIDCSI image of a corn oil phantom on the axial plane at 7 T demonstrate the feasibility of the proposed method. A preliminary proton image of a mouse on the sagittal plane is also acquired using the proposed dual-tuned volume coil at 7 T, illustrating a fairly uniform B(1) field and sufficient image coverage for imaging in mice.