磁致伸缩换能器辐射板形状对声场分布的影响

磁致伸缩换能器可作为热声制冷机的声源装置,辐射板的形状直接影响声压输出效率,从而影响制冷效果。为提高换能器工作效率、减小换能器体积,辐射板需在Terfenol-D棒的激励下产生大振幅、高频率的活塞振型。针对这一问题,应用ATILA软件分析了磁致伸缩换能器辐射板形状对谐振腔振动幅频特性的影响以及对谐振腔内声场分布的影响。结果表明:相同激励条件下,凹球面辐射板出现活塞振型时振幅最大,对应谐振腔中声压幅值最高;谐振腔端面形状为凹球面时,具有聚焦声压幅值的作用;端面形状为凹发射端-凸反射端组合的谐振腔内声压幅值最高。以上结论为合理设计辐射板、谐振腔两端面组合形状提供了参考。     

Sound field of a baffled sound source covered by an anisotropic rigid-porous material

A theoretical approach for the sound field of a piston sound source covered by a finite thickness layer of anisotropic rigid-porous material is presented. The formulation is an extension of the method worked out by Amedin et al. [Sound field of a baffled piston source covered by a porous medium layer. J Acoust Soc Am 1995;98(3):1757]. First, in the present study the sound field of a point source is described by cylindrical waves. Then, with the proper boundary conditions, the sound pressure radiated from a piston source covered by a layer of anisotropic porous material can be calculated. The effects of frequency and bulk density of material on the sound propagation in an anisotropic porous material are studied. Finally, the effect of anisotropy is discussed.     

脉冲超声换能器声场测试系统的设计

脉冲超声换能器是超声检测的关键部件,为了获取其声场特性参数,该文基于小球反射法,采用虚拟仪和单片机技术设计了工业用圆形晶片活塞声场测试系统。系统的程控交互界面采用美国国家仪器公司研制开发的图形化编程软件LabVIEW设计,通过调用动态链接库与系统核心硬件超声发射接收卡进行数据通信及对其功能进行设置,同时系统上位机通过RS232串口与下位机单片机通讯,实现对三轴扫查平台的多种扫查方式控制。该系统可实时显示脉冲换能器声压分布图像,并可通过对声压分布数据实现对换能器近场长度及扩散角等参数的测量。     

声源分布和超声频率对清洗声场均匀性的优化*

驻波和换能器指向性等影响声场均匀性,造成清洗死角,影响清洗效果。采用COMSOL仿真软件建立了单个换能器位于底部的三维模型,通过染色法实验结果验证模型的有效性。研究了换能器同时位于底部和侧面、多排换能器位于底部时的声场,用声压幅值相对标准差来量化均匀性,发现该两种换能器分布方式能够有效优化声场均匀性。通过调节频率研究频率对声场的影响,进一步优化声场均匀性。对声源分布的确定、频率的选择以满足声场均匀化需求有指导意义。     

Minimization of sound radiation from baffled beams through optimization of partial constrained layer damping treatment

An optimization study is presented with aim to minimize the sound power radiated by a simply supported, baffled beam with constrained layer damping (CLD) treatment. The governing equation of motion for the calculation of time-harmonic response of a partially CLD covered beam is derived first on the basis of energy approach. Assumed-modes method is used to solve the equation with obtained frequency response functions at different beam locations, which are further used for the calculation of its radiated sound power into half free-space by using Rayleigh’s integral. The optimization problem is then formulated to minimize the sound power radiated by the beam over a frequency range of interest covering multiple resonant modes. A genetic algorithm-based penalty function method is employed to search for the optimum of location/length of the CLD patch and the shear modulus of viscoelastic layer. Optimal results show that for a simply supported beam with a transverse force applied at its central location, it is not necessary to fully cover the structure using CLD patch in order to achieve the largest reduction in the sound power radiated by the beam over a frequency range. With inclusion of the amount of damping material to be minimized, the optimal CLD coverage length is only one-fourth of the base beam’s. Moreover, the optima of three design variables, the CLD coverage length, location on the beam and the shear modulus of viscoelastic layer, are highly relevant to each other.     

波叠加法在结构辐射声功率计算中的应用

描述了用波叠加法来计算任意形状辐射体的辐射声功率的方法。该方法在给定辐射体表面的振动速度后就可求解辐射源的强度,进而求解辐射体表面声功率。文中以脉动球源的辐射问题为列,讨论了波叠加法在应用过程中对单元、节点数目以及单元形状的敏感性。通过将该方法计算结果与解析结果进行对比表明,运用此方法在保证较高精度的前提下能明显减少计算所需的单元节点数,从而节省时间提高计算效率。     

电火花声源的某些特性

文中给出了电火花声源的压力波形及其频谱图，着重讨论了储能与压力波峰值P1m,和半峰值之间P1m/2的时间t1之间的关系，以及刚性圆筒内放电时边界对P1m和t1的影响。     

论声压级平均算法

本文阐述了求声压级平均值的几种算法,特别论述了对声压级数据直接进行算术平均的运算方法。     

A comparative study on the modeling of sound pressure field distributions in a sonoreactor with experimental investigation

In sonochemical reactors the effect of emerging cavitation bubbles has significant influence on the amplitude and structure of the developing sound field. Calculations show that the damping parameter and the phase velocity may, depending on the pressure amplitude, change by several orders of magnitude. For example, the sound velocity in water comes to 1500 ms⁻¹, whereas in a bubbly liquid it may decrease to 20 ms⁻¹, which is much below the velocity of sound in air (about 340 ms⁻¹). In this paper, a method of calculating the time dependent three-dimensional pressure field in sonochemical reactors of various shapes is presented. It takes into account inhomogeneous distributed wave parameters which are a function of the spatial depending pressure amplitude. The modeled results are then compared with experimentally measured values of a certain kind of reaction vessel. The agreement is found to be satisfactory.     

求解水中加肋板声辐射特性的虚拟声源法*

发展一种利用虚拟声源离散声场的方法求解加肋板在水中的声振耦合问题。由波叠加原理和单元体积速度匹配的原则,根据离散的结构单元满足的动力方程和结构与介质的交界相容性条件,确定虚拟声源强度,计算结构的声辐射功率。本文以简支矩形加肋板为例,在不获得结构表面振速和声压的情况下,计算了结构在水中的声辐射功率,并与解析方法计算的结果进行了比较,表明了该方法具有较好的计算精度。     

Studies on the properties of flow-induced oscillation and sound radiation in streamlined protuberant special cavities

I.IntroductionAsanuidpassingthroughthecavityatcertainflowrate,themediuminthemouthandthccavityisoscillatingandsoundisradiated.Noton1ystochasticturbu1encenoiscispossi-blyproducedbutsinglefrequencysoundofspecia1lydesignatedpitchisalsoproduced.Andthusthespcctrumofthcradiatedsoundisshownascontinuousspectrumandcharacteristiclinespcctrum.Inthiscascwcmaycallitflow-inducedosci1lation.Flow-inducedoscillationandsoundradiationcanbeproducedasafluid(waterorgas)passingthroughthecavitybysinkingcavityunderint…     

弯管对末端带弹性障板充液管路辐射声能量的影响

基于声固耦合有限元方法建立了末端带弹性障板的充液管路数值模型,重点分析了不同激励下弯管对管口辐射声能量的影响。结果表明:弯管引入的高阶周向模式耦合使结构振动和流体声传播都发生明显改变,以致系统辐射声能量及主要能量贡献源也发生转移,并随激励方式和频率而不同。对本文管路模型,平面波激励下弯管系统在低频的结构辐射声能量明显增加,在高频段呈流体声与结构声交替主导的特点。径向力激励下直管系统的总声能量几乎全部来自于弹性障板辐射结构声,而弯管的声固耦合使得管口流体声功率显著增加。在轴向力激励下弯管耦合使系统总辐射声功率显著下降的同时管出口的流体声功率反而增加。     

Orthogonal contributor number for the measurement of sound power

Orthogonal contributors to a global error represent a very efficient design method in terms of both sensing and control of noise radiation. In practice the price of a sensing system will be determined by the number of errors it must resolve. Therefore predicting the most efficient way of measuring radiation power is an important problem. Recently work has compared sensing the number of vibration modes to the number of orthogonal contributors to radiated power. The required number of vibration modes was based on the proximity of the structural mode resonance frequency and the excitation frequency. While ultimately this technique will result in a valid estimate of radiated power, it is shown here that the number of structural modes can be minimized by first considering orthogonal radiators based on structural mode amplitudes. Two disturbance cases are considered: a point force and an even disturbance coupling to each structural mode. Also, under these conditions the practicality of estimating the number of orthogonal radiators when it is assumed that each contributor is equal in amplitude is examined. Finally in an attempt to optimism the number of signals to be sensed, a variable error margin for the estimate of power, based on the ratio of the sound power at each frequency to the maximum peak in the considered frequency range is proposed and analyzed.     

硅油介质中矩形电容式微机械超声换能器发射与接收声场特性研究*

与传统压电式超声换能器相比,基于微机电系统微加工技术制备的电容式微机械超声换能器(CMUT)具有频带宽、灵敏度高、一致性好、易于集成等优势,在医学超声成像中具有广阔的应用前景。该文针对研制的矩形CMUT器件,开展硅油介质中CMUT发射、接收声场特性的理论分析及实验验证研究。首先,针对CMUT阵元结构特征和工作原理,根据指向性函数理论和Bridge乘积原理,建立了矩形CMUT阵元指向性函数分析模型。此基础上,分析微元数目以及谐振频率对CMUT指向性的影响规律。最后,针对7 mm×7 mm二维矩形CMUT在硅油介质中的发射和接收特性进行了实验验证,测试表明发射指向性曲线与仿真理论曲线基本吻合;此外,CMUT接收与发射指向性的测试表明,收发指向性具有一致性,从而验证了声场的互易性。该文的研究对CMUT器件的封装设计以及基于CMUT阵列的乳腺超声CT成像系统的研制具有重要参考价值。     

水听器线列阵近场声压测量误差实验研究

本文介绍了用于近场声压的测量水听器中阵元水听器测量声压的可靠性检验方法和实验结果,提出了元水听器测量球面波场中声传播衰减的曲线与现想球面波声场中场传播衰减的曲线对比的检验,要用球面声源声中心测量值对收发距离进行修正的方法,实验水池中对线列阵上十元水吸器在球形声源水池中进行了传播衰减曲线的测量分析,验证了基阵的弱散散射性能,表明线阵可用于距离小至1／7波长的极近场的扫描测量。     

Vibration analysis and sound field characteristics of a tubular ultrasonic radiator

A sort of tubular ultrasonic radiator used in ultrasonic liquid processing is studied. The frequency equation of the tubular radiator is derived, and its radiated sound field in cylindrical reactor is calculated using finite element method and recorded by means of aluminum foil erosion. The results indicate that sound field of tubular ultrasonic radiator in cylindrical reactor appears standing waves along both its radial direction and axial direction, and amplitudes of standing waves decrease gradually along its radial direction, and the numbers of standing waves along its axial direction are equal to the axial wave numbers of tubular radiator. The experimental results are in good agreement with calculated results.     

Experimental implementation of a low-frequency global sound equalization method based on free field propagation

An experimental implementation of a global sound equalization method in a rectangular room using active control is described in this paper. The main purpose of the work has been to provide experimental evidence that sound can be equalized in a continuous three-dimensional region, the listening zone, which occupies a considerable part of the complete volume of the room. The equalization method, based on the simulation of a progressive plane wave, was implemented in a room with inner dimensions of 2.70 m × 2.74 m × 2.40 m. With this method, the sound was reproduced by a matrix of 4 × 5 loudspeakers in one of the walls. After traveling through the room, the sound wave was absorbed on the opposite wall, which had a similar arrangement of loudspeakers, by means of active control. A set of 40 digital FIR filters was used to modify the original input signal before it was fed to the loudspeakers, one filter for each transducer. The optimal arrangement of the loudspeakers and the maximum frequency that can be equalized is analyzed theoretically in this paper. The presented experimental results show that sound equalization was possible from 10 Hz to approximately 425 Hz in the listening zone. A flat frequency response with deviations within ±5 decibels from the desired value was achieved. A higher demanding performance with deviations within ±1.5 decibels from a flat frequency response was attained in the interval between 20 Hz and 280 Hz. At the same time, the impulse response was quite well approximated to a delayed delta function in the listening zone. Examples of the spatial distribution of the sound field are also shown.     

Analysis of errors when using the similar source method to estimate sound fields

The similar source method (SSM) uses an imaginary source distribution to estimate radiated and scattered sound fields. The error analyses in the present study are for possible numerical errors by SSM, solutions of the problem of singularity and non-unique solution by SSM and the effects of possible errors in measurements on the estimation of the sound field by SSM.     

Measurement of sound absorption coefficients of flat surfaces in a workshop

To improve the acoustic treatment of facings and provide appropriate solutions for noise control at workplace, it is necessary to develop methods of acoustic characterization of the walls in industrial halls. Sound absorption coefficient measurement in industrial rooms is however quite a difficult task because of the partially reverberant conditions. This work describes the measurement of the sound absorption coefficient of flat panels subject to small angle sound incidence, in an industrial hall using an experimental device equipped with an acoustic array. The directivity of this array has been optimized so that the major part of the received acoustic energy would come from one portion only of the investigated facing, this, in turn attenuating the reflected beams due to the reverberation. This new device includes an impulse sound source targeting the panels. The present article focuses mainly on the sound source design and implementation. It also describes some sound absorption measurements carried in a semi-anechoic chamber and in an industrial hall in order to examine the performance of the device. Sound absorption coefficients of several standard liners obtained through this device have been compared to those resulted from the two microphone technique.     

未知耦合腔体积活塞发声器声压级的检测

本文简要介绍了活塞发声器的工作原理及其声压级的测量原理，着重分析了未知耦合腔体积活塞发声器的有效体积与声压级的测量方法。