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。     

刚性圆柱体上圆阵波束形成性能分析

以环绕在刚性圆柱体上的均匀圆阵为阵列模型,分析了刚性圆柱体对圆阵响应的影响,在声场分解所得到的相位模式空间,推导了相位模式波束形成阵列和延迟求和波束形成阵列的白噪声增益和指向性指数的定量表达式,分析了它们在不同频率段的变化规律。在存在和不存在刚性圆柱体两种情况下,对两种阵列性能进行了对比分析。研究了圆阵与圆柱体之间存在间隙时对阵列接收信号及阵列性能的影响。仿真结果表明,在两种情况下相位模式波束形成处理都具有频率不变的指向性,但在低频段牺牲了阵列的鲁棒性;延迟求和波束形成处理在整个频率段具有较好的鲁棒性,但随频率的降低其波束指向性下降,直至变成各向同性阵列。存在刚性圆柱体时,两种阵列鲁棒性均有了一定的提高,前者的指向性不变,而后者的指向性得到了提高。圆阵与圆柱体之间的间隙会降低阵列在高频段的鲁棒性。      

Nearfield broadband array design using a radially invariant modal expansion

This paper introduces an efficient parameterization for the nearfield broadband beamforming problem with a single parameter to focus the beamformer to a desired operating radius and another set of parameters to control the actual broadband beampattern shape. The parameterization is based on an orthogonal basis set of elementary beampatterns by which an arbitrary beampattern can be constructed. A set of elementary beamformers are then designed for each elementary beampattern and the desired beamformer is constructed by summing the elementary beamformers with frequency and source-array distance dependent weights. An important consequence of our result is that the beamformer can be factored into three levels of filtering: (i) beampattern independent elementary beamformers; (ii) beampattern shape dependent filters; and (iii) radial focusing filters where a single parameter can be adjusted to focus the array to a desired radial distance from the array origin. As an illustration the method is applied to the problem of producing a practical array design that achieves a frequency invariant beampattern over the frequency range of 1:10 (which is suitable for speech acquisition using a microphone array), and with the array focused either to farfield or nearfield where at the lowest frequency the radial distance to the source is only three wavelengths.     

传声器阵列对高频弱声源的声成像识别方法

研究了传声器阵列对高频弱声源的识别定位方法。该方法根据高频声源的指向性和阵列探测特性等特点,提出了利用信噪比加权方法提高有效阵元对声成像的贡献,根据信噪比的大小对每个阵元添加不同的权值,可以显著提高传声器阵列对高频弱声源的声像清晰度。仿真分析了阵元加权和不加权两种方法对阵列声成像结果的影响,以某型号笔记本电脑电路板噪声为对象进行的实验表明,在阵列测量中充分利用有效阵元信号可以实现对声压级低达10~20dB的微弱噪声源的精确测量。      

A method of improving overall resolution in ultrasonic array imaging using spatio-temporal deconvolution

In this paper a beamforming method for ultrasonic array imaging is presented that performs both spatial and temporal deconvolution based on a minimum mean square error (MMSE) criteria. The presented MMSE receive mode beamformer performs a regularized inversion of the propagation operator for the ultrasonic array system at hand. The MMSE beamformer accounts for the transmit and receive processes, defined in terms of finite array element sizes, transmit focusing laws and electrical transducer characteristics. The MMSE beamformer is compared to the traditional delay-and-sum (DAS) beamformer with respect to both resolution and signal-to-noise ratio. The two algorithms are compared using both simulated and measured data. The simulated data was obtained using ultrasonic field simulations and the measured data was acquired using a linear phased array imaging wire targets in water. The results show that the MMSE beamformer has superior temporal and lateral resolution compared to DAS. It is also shown that the MMSE beamformer can be expressed as a filter bank, which enables parallel processing at high frame rates.     

Beamforming correction for dipole measurement using two-dimensional microphone arrays

In this paper, a beamforming correction for identifying dipole sources by means of phased microphone array measurements is presented and implemented numerically and experimentally. Conventional beamforming techniques, which are developed for monopole sources, can lead to significant errors when applied to reconstruct dipole sources. A previous correction technique to microphone signals is extended to account for both source location and source power for two-dimensional microphone arrays. The new dipole-beamforming algorithm is developed by modifying the basic source definition used for beamforming. This technique improves the previous signal correction method and yields a beamformer applicable to sources which are suspected to be dipole in nature. Numerical simulations are performed, which validate the capability of this beamformer to recover ideal dipole sources. The beamforming correction is applied to the identification of realistic aeolian-tone dipoles and shows an improvement of array performance on estimating dipole source powers.     

Localization of virtual sound sources with bilateral hearing aids in realistic acoustical scenes

Sound localization with hearing aids has traditionally been investigated in artificial laboratory settings. These settings are not representative of environments in which hearing aids are used. With individual Head-Related Transfer Functions (HRTFs) and room simulations, realistic environments can be reproduced and the performance of hearing aid algorithms can be evaluated. In this study, four different environments with background noise have been implemented in which listeners had to localize different sound sources. The HRTFs were measured inside the ear canals of the test subjects and by the microphones of Behind-The-Ear (BTEs) hearing aids. In the first experiment the system for virtual acoustics was evaluated by comparing perceptual sound localization results for the four scenes in a real room with a simulated one. In the second experiment, sound localization with three BTE algorithms, an omnidirectional microphone, a monaural cardioid-shaped beamformer and a monaural noise canceler, was examined. The results showed that the system for generating virtual environments is a reliable tool to evaluate sound localization with hearing aids. With BTE hearing aids localization performance decreased and the number of front-back confusions was at chance level. The beamformer, due to its directivity characteristics, allowed the listener to resolve the front-back ambiguity.     

Investigations on the balloon as an impulse source

Measurements of impulses produced by bursting balloons are presented. Various sizes of balloons were popped with a mechanical device in an anechoic chamber and recorded with a spherical microphone array. The power responses and directivity of the balloons are analyzed. Results indicate that power responses have two emphasized frequencies which depend on balloon size and inflation level. Larger balloons radiated more energy and higher inflation levels resulted in stronger high frequency content. Balloon directivity patterns are stable over repetitions. However, balloons do not radiate omnidirectionally. The degree of omnidirectionality improves with balloon size and for midrange frequencies.     

A new microphone system for near whispering

A new microphone system was developed to monitor the human voice near the microphone in a noisy environment. The system is equipped with two special functions in addition to the usual microphone functions: reduction of air-blow effects by the mouth and focused reception to a sound source. A wind filter was developed to reduce the air-blow effects from the mouth during speaking. This filter is a plate perforated by an array of small holes; the method used to design the filter is also presented. To achieve focused reception, four microphones were used in conjunction with a new signal-processing method. The proposed signal-processing method effectively increases the directivity in the desired direction. Additionally, it provides the system with focusing on the source since the source is located adjacent to the system. A prototype of the proposed system was fabricated and subjected to performance tests. The results showed that air-blow effects can be reduced by up to 20 dB and the directional gain is more than 4 dB. The proposed microphone system shows such good performance that it can be used in mobile phones for whispering communication.     

传声器失配误差对差分传声器圆阵主瓣指向的影响特性

从理论上导出了传声器失配误差对适用于任意阵元数的一阶和二阶差分传声器圆阵的主瓣指向影响规律。揭示了传声器相位误差可造成一阶差分传声器圆阵主瓣指向产生反转现象,是影响其主瓣指向的主要因素。而对于二阶差分传声器圆阵,传声器相位误差和增益误差均可导致其主瓣指向产生反转现象和严重指向误差,进而造成阵列指向性因子严重下降,尤其在低频处失配误差的影响更为显著。然后给出了确保差分传声器圆阵主瓣指向正确时阵列设计参数所需满足的条件,并在此基础上进行了传声器失配误差的容差分析。分析结果表明,随着阵元数增多,失配误差的容差范围增大,差分传声器圆阵对传声器失配误差的敏感性相应降低。      

水下应用的电容式微机械超声换能器阵列设计

为提高用于水下成像的电容式微机械超声换能器的指向性,文中用ANSYS力电耦合分析法设计了工作频率为400 k Hz的收发一体传感器的结构参数并完成了实验验证。同时研究了阵列设计方法,分析了电容式微机械超声换能器阵列各参数对指向性的影响,完成了从微小敏感单元到阵列的设计,实现了阵列指向性的优化设计。该阵列为16阵元的线阵,阵元间距为1.925 mm,阵元宽度为1.82 mm。进行了水下指向性测试,实验表明该线阵的-3 dB主瓣宽度为5?,最大旁瓣级为-13.5 dB,对称性好。该设计是实现较远距离的探测,提高成像分辨率的前提。     

传声器阵列波束比判决语音增强方法

针对单一波束形成器难以深度抑制空间相干干扰的问题,提出了一种综合了最小方差无畸变响应波束形成器与对称子阵延时求和波束形成器的语音增强方法。定义了一种波束输出比因子,根据该因子在目标声区域和干扰声区域的幅值变化,给出了采样协方差矩阵对角加载量的调整方法,并进一步利用该因子在后滤波环节对空间干扰进行判决滤波。文中对判决滤波时的上限阈值和下限阈值的实时更新方法给出了说明。所提出的算法能进一步抑制空间干扰和噪声,且可满足实时需要。在传声器圆阵上的实验表明,该方法在输出信干噪比及语音质量上,均优于经典对角加载算法及采样协方差矩阵扫描重构算法。      

cMUT阵元的声学分析与环形扫描成像

电容式微机械超声换能器(cMUT)具有宽带宽、灵敏度高、机械阻抗低和与电子电路集成制造等优点.由于超声换能器声场设计的好坏决定了成像质量的优劣,为了明确阵元参数与辐射声场的关系,该文对不同的阵元参数进行了计算仿真.与压电陶瓷超声换能器的结构不同,cMUT阵元是由多个电容单元(cell)并联构成.因此分析了cell的半径...     

球谐域混叠消除最优波束形成方法EI北大核心CSCD

为解决现有的球谐域混叠消除波束形成方法设计目标单一、难以很好地兼容多变的应用场景的问题,提出了球谐域混叠消除最优波束形成方法,并建立了其二阶锥规划形式的多重约束凸优化数学模型。得益于该数学模型,提出了旁瓣约束的混叠消除最大指向性波束形成器、鲁棒的混叠消除最大指向性波束形成器、混叠消除最小方差无失真响应波束形成器、零点约束的混叠消除最大指向性波束形成器。提出方法继承了现有球谐域混叠消除波束形成方法的混叠消除功能,且能够在指向性指数、白噪声增益、旁瓣水平等多个冲突的性能指标之间寻求适宜折中,便于用户根据实际应用需求灵活地调整约束参数得到特定场景下综合性能最优的波束形成器。     

球谐域类正则化宽带超指向性波束形成算法

提出一种球谐域类正则化宽带超指向性波束形成算法,通过结合超指向性波束形成器与延迟求和波束形成器控制阵列白噪声增益和指向性因数,推导类正则化宽带超指向性波束形器的球谐域表达式。在此基础上设计新的可控指向性因数波束形成器,可在不显著放大低频白噪声的前提下实现设定的波束宽度。采用32元球阵的仿真结果表明,对于语音测试场景,类正则化波束形成器的最高PESQ得分相比于传统的超指向性波束形成器与延迟求和波束形成器分别提高了约0.5和0.4,平均词错率分别减少了约9.5%和8.1%。主观测试实验也表明类正则化波束形成器在方向性噪声和扩散场噪声环境下都可以获得更好的主观听觉感受。利用实验数据对算法性能进行测试,实验结果同样验证了该方法在实际声学环境中的有效性。      

Array gain for a conformal acoustic vector sensor array:An experimental study

An acoustic vector sensor can measure the components of particle velocity and the acoustic pressure at the same point simultaneously, which provides a larger array gain against the ambient noise and a higher angular resolution than the omnidirectional pressure sensor. This paper presents an experimental study of array gain for a conformal acoustic vector sensor array in a practical environment. First, the manifold vector is calculated using the real measured data so that the effects of array mismatches can be minimized. Second, an optimal beamformer with a specific spatial response on the basis of the stable directivity of the ambient noise is designed, which can effectively suppress the ambient noise.Experimental results show that this beamformer for the conformal acoustic vector sensor array provides good signal-tonoise ratio enhancement and is more advantageous than the delay-and-sum and minimum variance distortionless response beamformers.     

融合插值点优化的多项式结构宽带波束形成器设计方法*

多项式结构设计方法是主瓣指向可调宽带波束形成器设计的一类重要方法。多项式结构的阶数是有限的,导致主瓣实际指向与期望指向之间存在偏差,因而影响了波束形成器的指向性指数。针对这一问题,该文提出了一种基于插值点优化的多项式结构宽带波束形成器设计方法。首先,引入多项式结构插值点处阵列响应的空间导数约束,以减小主瓣指向偏差;进而利用粒子群优化算法对多项式结构中的插值点进行优化,以充分利用插值点位置提供的自由度进一步提升多项式结构宽带波束形成器的性能。优化设计结果表明,与现有设计方法相比,该文提出的方法不仅降低了主瓣的指向偏差,同时也提高了指向性指数,有效改善了多项式结构宽带波束形成器的性能。     

Design of robust broadband beamformers using worst-case performance optimization for time-domain spherical microphone arrays

Spherical array modal beamformers are known to be sensitive to microphone mismatches. To combat the problem, robust design of spherical broadband beamformers with the time-domain implementation structure using the Worst-Case Performance Optimization(WCPO) is studied. It is shown that the conservativeness of the upper error bound on beamforming response is the primary factor to degrade the performance of the existing WCPO-based approach. Then an improved design approach for spherical broadband beamformers is presented using a stricter upper error bound on beamforming response. Theoretical analysis shows that the cost function of the proposed design is smaller and the range of feasible set of the proposed design is also larger when compared with the existing design. Moreover, a scheme on constraint specification has been proposed to reduce fluctuation of beamforming response over frequency at steering direction to alleviate signal distortion. Simulation results show that the proposed design outperforms its existing counterparts and exhibits a lower sidelobe level under the same condition of microphone mismatches.     

宽带恒定束宽波束形成器的设计与实现

本文提出了一种设计宽带恒定束宽波束形成器的方法,这对应用于海底探测和分类问题的声纳系统来说十分重要,对于给定频带宽度的信号,选择一定数量的频率点来表达其频率响应,对于一个给定的频点,可以通过现有方法导出满足恒定宽要求的加权矢量,例如对于一个线阵列,可用切比雪夫多项多得到其加权矢量,因此对于一个具有Ｎ个阵元的宽带阵,如果选择Ｍ个频率点,可以得到一个ＮＭ的加权矩阵,这个矩阵的每一行代表一个阵元的频率响     

Optimization of Directivity of Point Source Array by Using Pseudostochastic Sequences

We investigate the methods to optimize the directivity of point source array by using pseudostochastic sequences. Maximum-length sequence （MLS） array and Quadratic-residue sequence （QRS） array are theoretically analysed, and their simulated responses are shown. The results indicate that pseudostochastic sequences can be used to optimize the directivity of point source array.