利用声辐射模态对声场进行重构

声辐射模态是定义在振动表面上的一组互相独立的基函数,描绘了振动表面的多极子辐射模式。本文利用声辐射模态对平板辐射的声场进行重构，并同时就频率和模态数对误差的影响进行了分析。针对复杂振动表面幅射的声场，重构时需正则化处理。数值计算结果和对应的理论值达到很好的吻合。     

利用声辐射模态重构任意目标的散射声场

水下目标散射声场的重构可以作为水下目标散射特性的研究基础。本文主要利用声辐射模态对水下目标进行散射声场重构研究。首先,在借助声传递矩阵给出的任意结构声辐射模态的流体域求解方法基础上,通过理论证明了目标的散射声压与声辐射模态具有函数关系。其次,借助声场分布模态的概念,同时考虑到声场分布模态病态及声压测量易受噪声污染,提出基于声辐射模态的正则化散射声场重构算法。仿真结果表明,波数越低,重构所需声辐射模态阶数越少,在较高波数时仅需总模态数的大约20%即可对声场进行重构。与基于边界元的声场重构算法相比,计算量减小了至少80%,且克服了赫姆霍兹积分方程最小二乘法仅对球壳结构的重构效果较好而不适用于长条形结构重构的缺陷。     

复杂结构声辐射模态的计算

结构辐射阻矩阵的特征向量就是其声辐射模态,复杂结构的辐射阻矩阵获取困难阻碍了声辐射模态理论的进一步应用。为此提出一种基于等效源方法的复杂结构辐射阻矩阵计算方法,由此形成了一套完整的计算复杂结构声辐射模态方法。最后通过仿真算例对影响结构辐射阻矩阵计算精度的因素进行了分析,给出了复杂结构辐射阻矩阵构造的一般原则。理论推导和数值仿真算例表明所提出的复杂结构声辐射模态计算方法是有效的。该方法简化了复杂结构声辐射模态的计算,计算效率较高。     

声场重构的声辐射模态阶数分析

利用声辐射模态法对椭球状声源辐射声场进行重构,分析了模态阶数对相对误差的影响,以及模态阶数与频率的关系;同时深入探讨了声源形状变化对模态阶数选取的影响。研究发现利用较少的模态阶数即可得到很好的重构效果,且声源形状的变化对重构所需模态阶数的影响较小,因此可将该方法用于任意形状声源的重构,体现了此方法在声场重构中的优越性。     

基于单元辐射叠加法的结构声源声场重建方法

为了提高分布式结构声源的声场重建精度,本文提出了基于单元辐射叠加法的结构声源声场重建方法.该方法首先利用声场叠加原理和结构振声传递特性,建立了结构声源表面振动与辐射声场之间的振声传递关系解析表达式,得到便于快速计算的振声传递矩阵,能够解决连续分布、相干结构噪声源的声传播模型精细化表征问题.然后利用振声传递矩阵作为传递算...     

弱耦合封闭声腔的声辐射模态理论与计算

有源结构声控制是耦合封闭声腔的声辐射控制的有效方法。在此前的研究中有学者提出了\     

调控明区声场重建性能和暗区声能量的综合控制方法

采用扬声器阵列的空间局部声场重建是指控制扬声器阵列输入的幅值和相位,使得目标声场聚焦于特定区域(明区)内,同时降低其他区域(暗区)的声能量。为满足车内乘客对独立视听环境需求的不断提高,研究车内局部声场重建。考虑到扬声器有驱动功率限制和传递函数存在测量误差,提出一种调控明区声场重建性能与暗区声能量平衡的鲁棒性控制方法(PSR-RC,Personal Sound Reproduction with Robust Control),采用路径跟踪法获得不同频率下的最佳权重因子。仿真结果与实车测试性能显示,PSR-RC算法保证明区重建声场性能的基础上,通过最小化暗区能量,获得了较好的明暗区声能量对比度。仿真与实车试验结果保持了较好的一致性,控制点区域的控制效果与非控制点区域的控制效果也保持了较好的一致性,验证了PSR-RC算法的正确性和可靠性。     

任意边界板结构的声辐射模态误差传感器的设计

获取声辐射模态伴随系数是基于声辐射模态理论进行主动结构声控制(ASAC)的重要环节。以往PVDF分布式传感器的设计难点是振速展开受边界条件的限制,其设计过程往往是针对特定边界条件展开的。本文在声辐射模态理论和两维分布式传感器的压电方程的基础上,将板表面振速分布用Legendre多项式展开,给出了两维板结构的PVDF传感器形状与边界条件无关的设计方法。这样设计得到的传感器能应用于任意边界条件和任意振速分布的两维板结构,且实时性好,拓宽了其应用范围。本文还分别以固定边界条件板及在该板中任取一小区域两种情况为例,证明了该设计方法的可行性。     

结构振动模态声辐射理论及试验研究

从结构振动声辐射的一般规律、自由声场的声功率辐射理论和结构振动模态原理入手,对结构振动模态的声辐射与外加激励、模态参数之间的关系进行了理论推导和研究,得到,当激振点不变,振动模态辐射的平均声压级的变化量与激振力级的变化量之比为1;若激振力不变,任意两点处激振振动模态辐射的平均声压级的变化量与相应点振型元素级的变化量之比为1.对以上结果试验验证表明:理论值与实测值基本相符.     

基于声辐射模态的有源控制解耦在固定支承板上的研究

基于声辐射模态的主动控制理论,以固定支承板为例,通过四组作动器在固定支承板上的布放,使其能分别控制不同阶声辐射模态辐射的声功率,来使控制方程解耦,从而设计了比较简单与稳定的单输入/单输出控制系统,模拟计算取得了较好的控制效果。同时本文对控制过程中的溢出等问题进行了一定的探讨。     

Acoustic source identification using a scanning laser Doppler vibrometer

This paper shows how a scanning laser Doppler vibrometer (LDV), an instrument designed to measure vibrations of structures or objects, can be used in a non-traditional fashion to identify acoustical sources. This is achieved by measuring the changes in the optical path induced by local fluctuation of the air refraction index to which the LDV is sensitive. The acoustical signal used is sinusoidal and may be recovered by scanning at a uniform rate over a subject area (continuous scan) parallel to the source axis and demodulating this signal. Due to the fact that the measured scan area is in fact a line integral over a measurement volume between the laser head and a rigid object needed to reflect the laser beam, multiple view planes around the axis of the acoustic source are usually measured. These are then passed through a tomographic algorithm, thereby reconstructing the full sound field. In this article however, only one view plane is measured, but the acoustic source is placed on a rotating surface with fixed rotational frequency, thereby imposing a modulation on the measured spectrum. Demodulation will allow reconstruction of the three-dimensional sound field.     

Theoretical and experimental investigation of holographic reconstruction and prediction of multi-source hybrid acoustic field

Recently, NAH has been developed as an efficient tool for noise identification, noise localization and acoustic field visualization. Compared with the traditional acoustic ra-diation calculation problem, the solving problem in the NAH is an inverse acoustic problem. By measuring partial acoustic field information, such as complex pressures or particle velocities on the hologram surface, but not the surface normal velocities of the vibrating body, the surface information can be reconstructed,…     

带电导体椭球表面的电荷密度与电场

利用极限情形推断了带电导体椭球表面的电荷密度与电场强度.     

Acoustic radiation force on a rigid cylinder near rigid corner boundaries exerted by a Gaussian beam field

Acoustic manipulation is one of the well-known technologies of particle control and a top research in acoustic field. Calculation of acoustic radiation force on a particle nearby boundaries is one of the critical tasks, as it approximates realistic applications. Nevertheless, it is quite difficult to solve the problem by theoretical method when the boundary conditions are intricate. In this study, we present a finite element method numerical model for the acoustic radiation force exerting on a rigid cylindrical particle immersed in fluid near a rigid corner. The effects of the boundaries on acoustic radiation force of a rigid cylinder are analyzed with particular emphasis on the non-dimensional frequency and the distance from the center of cylinder to each boundary. The results reveal that these parameters play important roles in acoustic manipulation for particle-nearby complicated rigid boundaries. This study verifies the feasibility of numerical analysis on the issue of acoustic radiation force calculation close to complex boundaries, which may provide a new idea on analyzing the acoustic particle manipulation in confined space.     

Reduction of sound radiation by using force radiation modes

The location of a vibration source within a machine is sometimes found to have a significant effect upon its radiated acoustic power. It is known that a simple reduction of vibration cannot always reduce the radiated acoustic power, so that treatments based on analysis of a structure’s vibration modes are not always effective. At the same time, radiation mode analysis is known to be a powerful tool for interpreting sound radiation since those modes are independent of a structure’s surface vibration. However, knowledge of the radiation modes alone cannot be used directly to understand the relationship between vibration source location and acoustic power radiation. In this paper, it is shown that the radiation mode concept can be extended to understand the relationship between acoustic power and driving force distribution by considering the product of the structure’s mobility matrix and the radiation modes: the resulting functions are here defined to be force radiation modes (f_rad-modes). An example is presented in which the acoustic power radiated by a simply-supported, baffled beam is reduced by using guidance provided by the structure’s force radiation modes. The results demonstrate that the force radiation modes can be used to guide the reduction of radiated acoustic power by changing the driving force location without the need to perform additional calculations or experiments.     

Acoustic field modeling for physiotherapy ultrasound applicators by using approximated functions of measured non-uniform radiation distributions

The strongest therapeutic effects in ultrasonic physiotherapy are mainly produced at the first centimeters, i.e. close to the applicator surface and, in general, only in the near-field zone. The acoustic field produced in practice by this type of transducers differs from the classical models because the vibration distribution on the real transducer surfaces is non-uniform. However, neither models using uniform distribution, nor those using typical non-uniform distribution patterns for the source accurately represent the radiation of this kind of transducers. Although this therapy is widely used and many efforts have been made in experimentally studying the patterns of ultrasound radiation produced during physiotherapy applications (IEC-61689, 1998), additional modeling researches still would be needed in order to achieve improved models giving field patterns closer to the measured ultrasonic results. In this paper, acoustic patterns produced from two source radiation functions are proposed and evaluated for field modeling of physiotherapy applicators. Both the functions are approximations to the pressure distribution measured close to the emitting surface and they are based on the modulation of the classical simply-supported function using either sinusoidal or Bessel-type distributions. The simply-supported function is accounted for the radiator-fixing condition and the modulation function simulates the complex vibration distribution of this kind of transducer. The modulator Bessel function is based on reports about Bessel-type vibration distributions found in piezoelectric disk resonators. The use of a selected sinusoidal segment represents another analytical option for obtaining an approximated behavior of the measured data in a real applicator. Both the field models are implemented using the finite element method (FEM) to obtain the numerical solution of wave equation at each point in the radiated space. The solution is reached by considering axisymmetric radiation in attenuation-free media. The results indicate the viability of applying an adequate model for acoustic field calculation by simulating the radiating distribution on the emitting surface as either sinusoidal or Bessel-modulated functions. Models using both the functions describe reasonably real behaviors, but those based on Bessel functions are better correlated with the measurements. The results for three commercial applicators indicate the possibility of representing, with adequate verisimilitude, the acoustic field radiated by physiotherapy ultrasound transducers using linear combinations of Bessel profiles describing the radiation source.     

一种小型化高功率微波辐射场功率密度测试系统

为解决现有高功率微波辐射场功率密度测量系统测量环节多、系统复杂以及长电缆无法适应复杂电磁环境测量等问题,研制了一款小型化、一体化辐射场功率密度测量系统。系统采用天线-耦合器-转换器作为接收前端,后端采用同轴信号处理单元,在屏蔽箱内完成信号衰减、功率探测及电光转换,可实现系统远程测量与监控,可用于连续波、单次脉冲、连续脉冲辐射场功率密度测量。同时,系统采用模块化校准,可有效降低测量系统不确定度。该系统具备30 dB动态,最小可测脉宽50 ns,可测辐射场功率密度100 MW/m²,系统结构紧凑,简便易携,采用光纤传输,抗电磁辐射,可实现X波段GW级高功率微波辐射场功率密度快速测量。