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     

基于声源预估的波叠加组合全息声源识别方法

为解决声源识别中旁瓣效应等因素引起的虚假识别结果问题,提出了基于声源位置预估的波叠加组合全息算法。应用波束形成算法进行声源位置的预估,将预估声压峰值点作为假定声源点,通过波叠加原理建立方程组,利用声源强度求解结果构造完整全息平面,通过声全息方法重新计算重建面声压。进行了仿真和实验验证,经该算法重构后,波束形成算法产生的虚假声源处的声压得以明显降低。表明该算法可以抑制旁瓣效应等因素的影响,提高声源识别的准确率。      

基于统计最优和波叠加的联合局部近场声全息

提出了一种基于统计最优近场声全息和波叠加法的联合局部近场声全息技术。首先利用两次统计最优近场声全息的声源定位结果来指导配置等效源,其后利用波叠加法进行局部声场重构。该技术适合于中低频声场的局部重建,计算快速,重建精度高;可以在测量数据有缺失的情况下重建声场。进行了脉动球声源模型的数值仿真,并在半消声室内对电机噪声源进行了实验,仿真实验都准确地重构了声源所辐射的外部声场。该技术可以重建任意类球形声源辐射的声场。      

超光谱空间干涉数据切趾函数与信噪比关系研究

干涉光谱技术在大气遥感、天文探测及地物勘察等诸多领域的应用是当前国内外研究热点,光谱重构作为遥感数据处理的重要环节与探测精度紧密相关。干涉数据由于有限光程差采样导致复原光谱出现频率泄露,切趾函数在光谱重构过程中可以起到平滑光谱、保持复原光谱和其他类型分光技术探测光谱一致性的作用,但同时会造成重构光谱的分辨率下降。已有研究表明切趾函数并没有提高反演精度,同时多个典型大气遥感载荷地面数据处理过程中并未使用切趾函数。空间外差光谱技术由于其诸多优点在国内外引起广泛关注,中科院安光所基于该技术成功研究出用于大气CO_2探测的原理样机。信噪比是光谱仪的核心指标之一,从信噪比、光谱分辨率和探测精度之间的关系出发研究切趾函数在干涉数据光谱重构中的影响。针对当前传统切趾函数并没有达到最优旁瓣抑制效果,以诺顿-比尔切趾函数为基础,在分辨率降低相同的情况下,获取最大的旁瓣抑制程度为判据构造了10种不同光谱展宽程度的切趾函数。利用SCIATRAN辐射传输模型分析了大气CO_2遥感探测中不同气体浓度造成的大气层顶的辐亮度差异,推导了典型条件下不同光谱分辨率满足1%探测精度需求的信噪比要求。以实验室空间外差光谱仪样机参数为基础,通过仿真干涉数据和本文构造切趾函数分析了不同切趾程度下光谱分辨率和信噪比的变化关系。最后利用实验室研制的样机开展了实验验证,通过观测稳定均匀积分球辐射源获取干涉数据在不切趾的情况下计算信噪比,以及干涉数据进行不同程度切趾后复原光谱信噪比。仿真和试验结果表明干涉数据由于切趾对噪声的抑制信噪比逐渐升高,同时造成光谱分辨率逐渐下降,而探测精度由于分辨率下降对光谱信噪比的要求也逐渐升高。探测精度对信噪比的需求提高明显高于切趾作用下光谱信噪比的升高趋势,仿真数据和实测数据信噪比分别在切趾程度大于1.6倍和1.8倍的情况下低于探测精度对仪器信噪比需求,即白噪声在噪声中占主导的情况下不切趾更有利于探测精度的保障。该研究结果可以作为干涉数据光谱重构的参考。     

FTIR单边干涉图相位校正技术的研究与改进

基于傅里叶变换红外光谱仪干涉图的单边过零采样和非对称性,对相位校正技术进行研究和改进。针对Mertz乘积法对切趾函数的匹配性要求高,干涉图非对称切趾旁瓣抑制效果差、光谱分辨率低的缺点,综合Mertz法和Forman法的特点提出一种改进的相位校正方法。采用对称化方法将单边干涉图变换为双边干涉图、对称切趾、傅里叶变换重建功率谱,并采用对称化的双边干涉图傅里叶变换求取高分辨率的相位谱,提高相位校正的精度。通过仿真分析了非对称窗函数较对称窗函数有比较宽的主瓣宽度、高的旁瓣幅值,分辨率降低;实验验证该改进的相位校正方法功率谱误差小、计算量少,且光谱分辨率比较高,达到2cm-1。     

大孔径声全息密集阵列的阵元数量去冗余方法

大孔径密集声全息阵列是实现对非平稳噪声成像的有效手段,通过现场快速成像可以掌握声场分布的动态特征。增加声阵列的孔径和阵元密度是提高近场声全息成像性能的主要措施,但随着声阵列阵元数量的增加,声压采集数据量增大,全息运算速度降低,全息成像动态性能下降,不利于现场即时成像分析。研究表明,在一定信噪比条件下,盲目增加阵元数量并不一定能提高近场声全息性能,为此,本文针对密集声全息阵列的阵元数量冗余问题进行研究,提出最优阵元数量估算方法,并采取去冗余处理。本文仿真和实验验证表明:针对一定信噪比条件下的密集阵列去冗余方法实际有效,可以在不降低近场声全息成像性能的前提下,降低运算量,提高全息成像速度,对于非平稳噪声的现场声全息成像测试具有实用意义。     

改善轴向分辨率的光瞳滤波器

给出了一种新型滤波器,它即能提高系统的轴向分辨率又不影响其横向分辨率。利用这种滤波器不可以控制远场旁瓣强度的最大值与主瓣强度最大值之比（Ｍ）,从而获得较好的超分辨效果,还根据扩展结果分析了光瞳滤波器的中间区对轴向分辨率的影响。     

改进粒子群算法的立体传声器阵列声成像系统阵形优化设计

提出改进的粒子群优化算法,获得波束方向图主瓣宽度和旁瓣级折中的优化立体阵形,避免基本实数粒子群算法仅采用旁瓣级或主瓣宽度一个性能指标优化而导致另一个性能指标恶化的问题,利用阵列视角限制进一步优化立体阵形并设计了声成像测量系统。改进的粒子群算法与基本粒子群算法仿真优化阵形比较表明改进粒子群算法设计的优化阵形在保持较窄的主瓣宽度的条件下具有较低的旁瓣级。阵列声成像测量系统的性能测量分析结果表明该系统的空间分辨率和旁瓣抑制能力与理论结果接近,验证了所提算法的有效性。      

基于支持向量回归的patch近场声全息研究

为了解决patch近场声全息中全息数据外推问题,提出一种基于支持向量回归的一步式patch近场声全息技术。该方法首先把初始全息面上的数据当成训练样本进行学习,构造出回归函数,然后利用回归函数实现全息数据外推,最后基于统计最优近场声全息进行重建。数值仿真和实验研究的结果表明:在各个分析频率下,该方法都可以实现小孔径全息面的近场外推。从近场声全息重建结果看,即使初始全息数据受到噪声干扰,该方法也是一种有效的patch近场声全息技术。      

多普勒差分干涉光谱仪大气风速反演过程中窗函数优化

多普勒差分干涉光谱仪是傅里叶变换型光谱仪,在大气风速反演过程中,偶延拓的反演光谱无法直接解出目标谱线的相位,而且在实际测量中反演光谱中含有的杂散光谱线、噪声等,使得复干涉图相位发生变化,最终导致反演风速值的偏差。所以,在对实际噪声环境下测得数据的处理过程中,获取反演光谱相位信息时需要对目标谱线进行提取。针对不同信噪比的干涉图,利用蒙特卡罗方法对不同线宽的不同窗函数的优化反演结果进行分析。结果表明:对于信噪比高于26.5dB的干涉图,线宽为4~5倍光谱分辨率的高斯窗函数是最优的窗函数优化方式;对于信噪比低于26.5dB的干涉图,线宽为7~12倍光谱分辨率的矩形窗函数的反演风速值更精确,是最优的窗函数优化方式,可以复原相位信息,反演出大气风速的近似值。     

三维空间非同步测量高分辨率声成像方法

为解决三维空间中声源成像分辨率低的问题,提出一种基于非同步测量的三维空间声成像方法.该方法首先通过移动球形传声器阵列扫描空间分布的声源,然后利用非同步测量技术近似得到大孔径、高密度的传声器阵列测量结果,最后通过传统波束形成算法成像.仿真及实验结果表明,该方法与单次测量下的波束形成方法相比,聚焦性能更好,空间分辨率高,可...     

A fast signal subspace approach for the determination of absolute levels from phased microphone array measurements

Phased microphone arrays are used in a variety of applications for the estimation of acoustic source location and spectra. The popular conventional delay-and-sum beamforming methods used with such arrays suffer from inaccurate estimations of absolute source levels and in some cases also from low resolution. Deconvolution approaches such as DAMAS have better performance, but require high computational effort. A fast beamforming method is proposed that can be used in conjunction with a phased microphone array in applications with focus on the correct quantitative estimation of acoustic source spectra. This method bases on an eigenvalue decomposition of the cross spectral matrix of microphone signals and uses the eigenvalues from the signal subspace to estimate absolute source levels. The theoretical basis of the method is discussed together with an assessment of the quality of the estimation. Experimental tests using a loudspeaker setup and an airfoil trailing edge noise setup in an aeroacoustic wind tunnel show that the proposed method is robust and leads to reliable quantitative results.     

Uncertainty of array-based measurement of radiated and absorbed sound intensity

Patch near-field acoustic holography (NAH) coupled with an array of sound intensity probes allows separating the sound field incident on a surface from the one radiated by the surface itself. Although the measurement principle has been successfully used to separate the noise source contribution from disturbing sources and/or noise reflections, the method accuracy has not been investigated in the literature. We describe the results of experiments meant to evaluate the uncertainty in the identification of noise radiated by vibrating panels with different absorption characteristics in presence of an incident acoustic radiation using the statistically optimized near-field acoustic holography. Measurement errors were evaluated through tests performed in controlled acoustic conditions. Results evidenced that the measurement uncertainty depends on the accuracy of the microphone array positioning and on the incident sound field. These conclusions were in agreement with the results obtained by simulations in the phase of instrument optimization.     

一阶指向可调差分阵列的前后向比分析与优化设计

一阶指向可调差分传声器阵列具有尺寸小、主瓣指向灵活可调、以及阵列响应不随频率变化等优点,因而在音频处理领域得到了重要关注。但差分传声器阵列对阵元失配误差较为敏感,在实际设计中需要予以考虑。前后向比直接反映了传声器阵列对后向噪声干扰的抑制程度,是差分传声器阵列设计中的重要指标。本文从理论上深入剖析了失配误差对一阶指向可调差分传声器阵列前后向比性能的影响,揭示了其中蕴含的规律。在此基础上,针对实际中同时存在随机失配误差情况,提出了一种最差性能优化设计方法。仿真实验和实测实验验证了本文理论分析的正确性和所提优化设计方法的有效性。      

Implementation issues of the nearfield equivalent source imaging microphone array

This paper revisits a nearfield microphone array technique termed nearfield equivalent source imaging (NESI) proposed previously. In particular, various issues concerning the implementation of the NESI algorithm are examined. The NESI can be implemented in both the time domain and the frequency domain. Acoustical variables including sound pressure, particle velocity, active intensity and sound power are calculated by using multichannel inverse filters. Issues concerning sensor deployment are also investigated for the nearfield array. The uniform array outperformed a random array previously optimized for far-field imaging, which contradicts the conventional wisdom in far-field arrays. For applications in which only a patch array with scarce sensors is available, a virtual microphone approach is employed to ameliorate edge effects using extrapolation and to improve imaging resolution using interpolation. To enhance the processing efficiency of the time-domain NESI, an eigensystem realization algorithm (ERA) is developed. Several filtering methods are compared in terms of computational complexity. Significant saving on computations can be achieved using ERA and the frequency-domain NESI, as compared to the traditional method. The NESI technique was also experimentally validated using practical sources including a 125 cc scooter and a wooden box model with a loudspeaker fitted inside. The NESI technique proved effective in identifying broadband and non-stationary sources produced by the sources.     

单层传声器阵列信号空间重采样的声波分离方法

为了重构非自由声场中目标声源的声场响应,提出单层传声器阵列信号空间重采样的声波分离方法.以球面波函数为基函数,建立由系列球面波函数叠加表达的声场数学模型.基于近场声全息原理,利用单层传声器阵列面上空间重采样形成的两组声压测量信号,求解基函数系数,并重构出传声器阵列两侧声源各自的声场响应,实现声波分离.使用脉动球和振动球共同作用的非自由声场,检验了数学模型以及传声器信号信噪比、传声器阵列形状和面积、声源中心位置、频率等关键参数对声波分离精度的影响,并在全消声室内进行了实验验证.最后,对单层传声器阵列重采样的声波分离方法的实施给出了建议.     

Optimized microphone deployment for near-field acoustic holography: To be, or not to be random, that is the question

Arrays with sparse and random sensor deployment are known to be capable of delivering high quality far-field images without grating lobes. This raises the question of whether or not this idea can be applied to near-field imaging as well. To answer this question that has not yet been widely investigated in previous research, numerical simulations are undertaken in this paper to optimize the microphone deployment for both far-field and near-field arrays with the latter being the main focus. In the simulation, a recently introduced near-field equivalent source imaging (NESI) technique is employed for the near-field imaging. Global optimization techniques including the simulated annealing (SA) algorithm and the intra-block Monte Carlo (IBMC) algorithm are exploited to find the optimal microphone position efficiently. The combined use of the SA and the IBMC algorithms enables efficient search for satisfactory deployment with excellent beam pattern and relatively uniform distribution of microphones. In the near-field optimization, a special kind of beam pattern and cost function definition is used for the multiple-input-multiple-output (MIMO) imaging problem. As indicated by the simulation results, random deployment of microphones is necessary to avoid grating lobes in far-field imaging. In the near-field simulation, all results suggest that the optimal near-field array is the uniform rectangular array (URA) and the random deployment presents no particular benefit in near-field imaging.     

稳健宽带波束形成器设计的低阶统计量法*

由于传声器阵列通常对阵元失配误差较为敏感,因此稳健波束形成器的设计已成为传声器阵列处理领域的研究热点之一。概率密度法是目前传声器阵列稳健波束形成器设计中的一类重要方法,但该方法所需的阵元失配误差的概率密度信息在实际中较难获取。针对这一问题,本文研究了基于阵元失配误差低阶统计量的稳健波束形成器设计方法,该方法仅利用在实际中较易获取的阵元失配误差的一阶和二阶统计量信息。本文分别研究了基于阵元失配误差低阶统计量的固定权和变加权最小二乘波束形成器设计,给出了两种波束形成器的相关设计理论。理论和仿真分析表明,在小误差条件下,低阶统计量法所设计的波束形成器仍保持与概率密度法相当的性能。     

Real-time near-field acoustic holography for continuously visualizing nonstationary acoustic fields

Near-field acoustic holography (NAH) is an effective tool for visualizing acoustic sources from pressure measurements made in the near-field of sources using a microphone array. The method involving the Fourier transform and some processing in the frequency-wavenumber domain is suitable for the study of stationary acoustic sources, providing an image of the spatial acoustic field for one frequency. When the behavior of acoustic sources fluctuates in time, NAH may not be used. Unlike time domain holography or transient method, the method proposed in the paper needs no transformation in the frequency domain or any assumption about local stationary properties. It is based on a time formulation of forward sound prediction or backward sound radiation in the time-wavenumber domain. The propagation is described by an analytic impulse response used to define a digital filter. The implementation of one filter in forward propagation and its inverse to recover the acoustic field on the source plane implies by simulations that real-time NAH is viable. Since a numerical filter is used rather than a Fourier transform of the time-signal, the emission on a point of the source may be rebuilt continuously and used for other post-processing applications.     

单层传声器阵列重建相干声场的近场声全息方法研究

针对传声器阵列两侧存在相干声源的非自由声场重建问题,提出基于球面谐波函数扩展近场声全息理论的相干声场重建方法。该方法在已知测量面两侧声源几何位置时,使用单层传声器阵列获取测量面处的声压分布,通过最小二乘法获得与目标声源和干扰噪声源响应对应的最优球波函数扩展项数和最优系数向量,结合测点位置的空间坐标进行声波分解,并分别重建出各声源在测量面上的声压分布。为了验证方法的有效性,分别给出了相干噪声源为球形声源和非球形声源的仿真验证,并在全消声室内对双扬声器产生的相干声场的重建进行了实验验证。结果表明:该方法对球形声源和非球形声源干扰下的声场重建都具有较好的效果,球形声源干扰下的重建精度更高。