基于声压梯度参考的部分场分解方法及实验研究

采用扫描测量方式得到的不相干声场需分解成完全相干的部分场后才能用于近场声全息重建. 现有的方法都是将声压作为参考进行部分场分解. 本文提出以声压梯度作为参考, 并建立一种基于声压梯度参考的部分场分解方法. 由于声压梯度比声压的衰减速度更快, 受到其他声源和环境噪声的影响比声压小, 所以以声压梯度为参考在分解完全相干的部分场过程中比以声压为参考更具有优势. 通过数值仿真和实验分析, 一方面验证了基于声压梯度参考的部分场分解方法的正确性和可行性; 同时通过与基于声压参考的部分场分解结果比较, 说明了基于声压梯度参考的部分场分解方法分解更稳健、结果更精确.     

基于波叠加法的近场声全息空间分辨率增强方法

提出一种基于波叠加法的近场声全息空间分辨率增强方法. 该方法在波叠加法的基础上,利用全息面声压信号求得布置在全息面附近的虚源面上的简单源源强,再根据求得的简单源源强实现对全息面声压的插值,进而利用插值后的全息面声压数据进行重建. 该方法可以提高近场声全息重建图像的空间分辨率,减少测量工作量,简化测量过程. 通过仿真对影响插值结果的参数进行了分析,给出了合理的选取范围;通过仿真和实验研究验证了该方法的有效性. 关键词： 波叠加法 近场声全息 空间分辨率     

基于简正波分解的不同阵列匹配场定位性能分析

针对利用不同阵列对浅海环境中水下目标的定位问题,基于简正波分解方法,对组合阵的目标声源定位性能进行了研究,着力解决在实际实验环境下定位性能不够高的问题,并降低实验设备布放难度.在浅海环境下,基于匹配场理论的声接收阵可实现目标的定位,但定位性能受阵形、阵元数目等影响.通过研究不同声接收阵的简正波分解矩阵,可以有效辨别不同阵形定位性能的优劣.仿真实验表明,当某一子阵简正波分解效果较差时,会降低组合阵的定位性能.基于实际实验的需求,在对短垂直阵和组合阵性能的研究中发现,由于水平阵对接收声场的定位模糊度函数中的旁瓣有抑制效果,从而造成模糊度函数表面上旁瓣较低,定位目标的主旁瓣比有所提升的现象.仿真实验表明,不同组合阵形的定位准确度均在90%以上,基于实际应用的考虑,组合阵无疑是对定位性能和实验复杂度的折中选择.     

孔隙地层震电测井波场分波分析

由于孔道的双电层结构和流体-固体耦合运动, 弹性波在孔隙地层中传播时会引起电磁场. 前人提出了基于这种耦合效应的震电测井方法, 但对井中震电波的特性缺少细致的分析. 本文对孔隙地层充流体井孔中点声源激发的震电耦合波的分波进行分析, 证明了井孔流体电磁波波数不是井内震电波场支点, 计算了地层电磁波支点、横波支点和快纵波支点对应的侧面波. 在利用辐角原理求出震电波场函数的复极点之后, 针对典型砂岩地层计算了震电波场模式波(包括泄漏模式)的频散曲线和声压、电场激发曲线. 计算了各个侧面波和模式波的电场激发强度与声压激发强度的比值(电声激发比), 发现纵波的电声激发比相对于横波和模式波更高, 而Stoneley波电声激发比的辐角对渗透率敏感, 其敏感性会随频率增大而增加, 随孔隙度增大而降低.     

横场伊辛铁磁薄膜的自旋波

本文在格林函数理论的框架内,研究横场伊辛铁磁薄膜系统的自旋波,分析了横场、表面特性等薄膜参数对自旋波频谱及谱强度分布的影响,证实在一定的参数条件下可以出现一致进动模和局域的表面模。 关键词：     

地震波传播路径追踪的波动方程方法

在地震勘探的地震波传播研究中,波场传播路径追踪是一项重要研究内容,通常采用射线理论追踪地震波传播路径.提出一种波动方程波场传播路径追踪方法,首先利用窗口Fourier框架展开技术对源点和目标点的波场进行角度分解,并计算它们的方向照明,然后利用角度相干技术获取源点和目标点间的波场传播路径.该方法可以有效考虑地下非均匀介质对地震波场传播的聚焦与散焦作用.     

运动声源识别的动态波叠加方法研究

为更好地识别运动声源并解决声源识别中的虚假声源问题,基于运动声源短时信号的Doppler频移特性, 建立运动声场的短时波叠加关系, 利用波束形成方法对声源点进行预估, 基于预估建立起多运动声源的动态叠加方程, 进一步通过波叠加方程的求解进行声源的计算, 从而创建一种可以用于运动声源识别的动态波叠加方法. 该方法可以有效识别运动声源, 将波叠加方法扩展到了运动声源测量领域, 并在不增加传声器数量以及改变阵列形式的条件下有效抑制运动声源重建中的旁瓣效应, 解决运动声源识别中的虚假声源问题. 仿真及实际运动声源的测量试验结果证明了该方法的有效性.     

适用于循环平稳声场的基于波叠加法的近场声全息技术

在原有的平面循环平稳近场声全息基础上，提出一种基于波叠加法的循环平稳近场声全息技术，可以对具有复杂表面的声源进行全息重建，重建的声源表面声压谱相关密度函数能反映出调制信号的信息.声源表面声压谱相关密度函数全息图形象地反映了调制信号在表面的强弱分布情况，可由此确定调制信号源的产生位置.仿真分析和实验验证表明，基于波叠加法的循环平稳近场声全息技术可以更准确地反映循环平稳声场的调制特性.该方法继承了波叠加法的优点，无需计算边界奇异积分，计算效率高、精度好.     

9.5 m高水平极化有界波电磁脉冲模拟器内场分布特性的初步实验研究

测量了9.5 m高的水平极化有界波电磁脉冲模拟器的内部场,并根据实验测量结果分析了该模拟器内场分布特性,包括一定区域内场均匀性的定量分析及模拟器内部有效测试空间的确定方法,进而对最低位置为距离地面2 m的有效测试空间进行了预估。实验结果表明：位于该模拟器双锥中心正下方且距离该中心5.5～7.5 m的测点场的峰值基本按照测点与双锥中心间距的倒数衰减,且随着测点与双锥中心间距的增大,因锥与极板不连续结构导致的波形变化在时间轴上滞后,而因地面影响导致的波形变化在时间轴上提前;在距离地面比较高的水平面上,两极板之间场的外泄方向场的衰减比双锥中轴线方向场的衰减更慢;该模拟器内部距离地面2 m的水平面上12 m×12 m的区域内所取测点的归一化场平均峰值约为0.678,归一化场平均峰值的标准偏差约为0.068 9,场的均匀性约为2.039 dB。     

利用场关联效应抑制瑞利型非简并四波混频的热背底

瑞利型非简并四波混频是测量物质超快纵向弛豫时间的有效手段,将场关联原理应用于具有热吸收的样品中瑞利型非简并四波混频的热背底抑制，给出了抑制热背底的条件，并通过数值模拟证明了其可行性. 关键词： 四波混频 场关联 超快测量     

A wave field synthesis approach to reproduction of spatially correlated sound fields

This article discusses an open-loop wave field synthesis (WFS) approach for the reproduction of spatially correlated sound fields. The main application concerns laboratory reproduction of turbulent boundary layer wall pressure on aircraft fuselages and measurement of their sound transmission loss. The problem configuration involves reconstruction of random sound pressure distributions on a planar reproduction surface using a planar array of reproduction monopoles parallel to the reproduction plane. In this paper, the WFS formulation is extended to sound fields with imposed time and spatial correlation properties (or equivalently imposed cross-spectral density in the frequency and wave number domains). Numerical examples are presented for the reproduction of a propagating plane wave, diffuse acoustic field and wall pressure in subsonic or supersonic turbulent boundary layers. The reproduction accuracy is examined in terms of the size of the source plane and reproduction plane, their separation, and the number of reproduction sources required per acoustic wavelength. While the reproduction approach cannot reconstruct sub-wavelength correlation scales of subsonic turbulent boundary layers, it effectively reconstructs correlation scales larger than the acoustic wavelength, making it appropriate for diffuse acoustic field and supersonic turbulent layers.     

Adaptive wave field synthesis for active sound field reproduction: experimental results

Sound field reproduction has applications in music reproduction, spatial audio, sound environment reproduction, and experimental acoustics. Sound field reproduction can be used to artificially reproduce the spatial character of natural hearing. The objective is then to reproduce a sound field in a real reproduction environment. Wave field synthesis (WFS) is a known open-loop technology which assumes that the reproduction environment is anechoic. The room response thus reduces the quality of the physical sound field reproduction by WFS. In recent research papers, adaptive wave field synthesis (AWFS) was defined as a potential solution to compensate for these quality reductions from which WFS objective performance suffers. In this paper, AWFS is experimentally investigated as an active sound field reproduction system with a limited number of reproduction error sensors to compensate for the response of the listening environment. Two digital signal processing algorithms for AWFS are used for comparison purposes, one of which is based on independent radiation mode control. AWFS performed propagating sound field reproduction better than WFS in three tested reproduction spaces (hemianechoic chamber, standard laboratory space, and reverberation chamber).     

Adaptive wave field synthesis for broadband active sound field reproduction: signal processing

Sound field reproduction is a physical approach to the reproduction of the natural spatial character of hearing. It is also useful in experimental acoustics and psychoacoustics. Wave field synthesis (WFS) is a known open-loop technology which assumes that the reproduction environment is anechoic. A real reflective reproduction space thus reduces the objective accuracy of WFS. Recently, adaptive wave field synthesis (AWFS) was defined as a combination of WFS and active compensation. AWFS is based on the minimization of reproduction errors and on the penalization of departure from the WFS solution. This paper focuses on signal processing for AWFS. A classical adaptive algorithm is modified for AWFS: filtered-reference least-mean-square. This modified algorithm and the classical equivalent leaky algorithm have similar convergence properties except that the WFS solution influences the adaptation rule of the modified algorithm. The paper also introduces signal processing for independent radiation mode control of AWFS on the basis of plant decoupling. Simulation results for AWFS are introduced for free-field and reflective spaces. The two algorithms effectively reproduce the sound field and compensate for the reproduction errors at the error sensors. The independent radiation mode control allows a more flexible tuning of the algorithm.     

波场合成中声像感知距离重建

声像距离是声像位置的重要信息,为了完整地描述重建声场中感知声像位置,需在虚拟声场中重建出声像距离。本文基于人耳对距离的感知机理,将镜像法引入波场合成技术中,通过模拟反射声来控制感知声像距离。基于\     

迭代重加权时域平面波叠加法的非稳态声场重建

提出了迭代重加权时域平面波叠加法,并应用于非稳态声场重建。该方法首先通过时域离散卷积得到全息面时域声压与虚源面时域波数谱离散状态公式;然后根据稀疏表示和迭代重加权,得到残差范数与加权解范数最小化问题表达式;最后将每一对波数下虚源面时域波数谱与时域传播核卷积叠加得到重建面上的时域声压。为了验证该方法的有效性,给出了激励板声源的仿真验证,并在半消声室内进行了实验验证。讨论了一些参数对该方法的影响,并通过与基于Tikhonov正则化的时域平面波叠加法比较,突出该方法的重建优势。仿真和实验结果表明,该方法对非稳态声场重建具有很好的效果,并且重建精度高。     

Partial field decomposition of multi-source cyclostationary sound field

The cyclostationary sound field is a kind of special non-stationary field which has obvious modulation phenomena. Conventional planar near-field acoustic holography (PNAH) technique cannot exactly reflect its modulation characteristics. If the cyclic spectral density (CSD) instead of the complex sound pressure is adopted as the reconstruction variable, the modulating wave and carrier wave components of the cyclostationary sound field can be extracted effectively. A new technique called cyclostationary PNAH utilizing the CSD is proposed in this paper. Based on this technique, the problem of partial field decomposition by singular value decomposition (SVD) of multiple incoherent cyclostationary sound sources is researched. The results of numerical simulation and experiments show that the CPNAH technique and SVD decomposition method are effective.     

Influence of the Number of Loudspeakers on the Timbre in Horizontal and Mixed-Order Ambisoncis Reproduction

Ambisonics is a series of flexible spatial sound reproduction systems based on spatial harmonics decomposition of sound field. Traditional horizontal and spatial Ambisonics reconstruct horizontal and spatial sound field with certain order of spatial harmonics, respectively. Both the Shannon-Nyquist spatial sampling frequency limit for accurately reconstructing sound field and the complexity of system increase with the increasing order of Ambisonics. Based on the fact that the horizontal localization resolution of human hearing is higher than vertical resolution, mixed-order Ambisonics (MOA) reconstructs horizontal sound field with higher order spatial harmonics, while reconstructs vertical sound field with lower order spatial harmonics, and thereby reaches a compromise between the perceptual performance and the complexity of system. For a given order horizontal Ambisoncis or MOA reproduction, the number of horizontal loudspeakers is flexible, providing that it exceeds some low limit. By using Moore’s revised loudness model, the present work analyzes the influence of the number of horizontal loudspeakers on timbre both in horizontal Ambisonics and MOA reproduction. The binaural loudness level spectra (BLLS) of Ambisoncis reproduction are calculated and then compared with those of target sound field. The results indicate that below the Shannon-Nyquist limit of spatial sampling, increasing the number of horizontal loudspeakers influence little on BLLS then timbre. Above the limit, however, the BLLS for Ambisoncis reproduction deviate from those of target sound field. The extent of deviation depends on both the direction of target sound field and the number of loudspeakers. Increasing the number of horizontal loudspeakers may increase the change of BLLS then timbre in some cases, but reduce the change in some other cases. For MOA, the influence of the number of horizontal loudspeakers on BLLS and timbre reduces when virtual source departs from horizontal plane to the high or low elevation. The subjective evaluation experiment also validates the analysis.