一种新型声隔离系统

水声换能器的收／发声隔离度决定了很多水声设备的性能优劣。介绍了一种新型声学隔离系统,该系统改变了声障板的设计思路,使换能器的收／发声串漏得到明显降低。通过偶极子原理,提出了一种提高收／发声学隔离度的方案。利用有限元仿真手段,计算并验证了该种方案的有效性。参照仿真模型,制作了一套声隔离系统样机,在1个倍频程的频带内,该系统的收／发声隔离度大于40dB。该声隔离系统提高了现有水下声目标模拟设备的性能。     

声透镜波束形成技术

介绍了研发的声线追迹程序和声场计算程序对声透镜波束形成的仿真结果,并与实际的透镜波束形成结果相比较。结果表明,仿真程序能够很好的模拟不同角度的入射声束的聚焦位置、波束宽度以及相对幅度,可以用于声透镜设计,大大减少声透镜制作过程中反复通过实验修改透镜参数的次数。     

中心棒哈特曼发声器声学特性研究

采用FW-H声模拟法,研究了中心棒的位置、长度和直径等因素对中心棒哈特曼发声器声学特性的影响,得出如下结论:无论中心棒置于谐振腔入口前端还是底部,只要中心棒一端处于气流入口到谐振腔入口段,哈特曼发声器就能产生较高的声压级;中心棒置于气流入口,且长度不超过喷流间距,会产生比普通哈特曼发声器更高的声压级;中心棒的半径有一个最佳值,数值模拟结果显示,不同半径中心棒哈特曼发声器声压级的大小顺序相应为:r=0.2mm、r=0.3mm、r=0.1mm、r=0.5mm,即半径r为0.2mm的中心棒哈特曼发声器产生的声压级较大,而半径r为0.5mm的声压级最较小;频谱分析发现,加中心棒会使哈特曼发声器的最大峰值频率变小。上述结论对中心棒哈特曼发声器的应用具有重要的指导意义。     

基于超声驻波场的水下颗粒操控研究

超声波产生的声辐射力可以实现对微小物体的操控。针对微米尺度颗粒在液体环境的操控问题,基于黏性介质中的声辐射力理论,建立由双凹球面聚焦超声换能器驱动下的水下颗粒操控模型。利用COMSOL软件仿真了模型的声场、声流场及颗粒操控动态过程,最后通过水下颗粒操控实验对仿真结果进行验证。研究发现,颗粒在水下操控过程受到声辐射力与声流曳力的共同作用,由声波干涉作用形成的局部驻波场主要依靠声辐射力将颗粒团聚在波节位置,但随着颗粒尺寸的减小,颗粒无法继续束缚,颗粒操控将由依靠声辐射力转变为声流曳力。此外声场强度的增加会增强颗粒操控的抗扰动能力。     

An Acoustic Meta-Skin Insulator

Acoustic metamaterials with artificial microstructures are attractive to realize intriguing functions, including efficient waveguiding, which requires large impedance mismatches to realize total side reflection with negligible transmission and absorption. While large impedance mismatch can be readily realized in an air environment, acoustic waveguiding in an underwater environment remains elusive due to insufficient impedance mismatch of state-of-the-art metamaterials. Here, a superhydrophobic acoustic metasurface of microstructured poly(vinylidene fluoride) membrane, referred to as a “meta-skin” insulator, which is able to confine acoustic waves in an all-angle and wide spectrum range due to tremendous impedance mismatch at stable air/water interfaces, viz., the Cassie–Baxter state is demonstrated. By utilizing the meta-skin insulator with broadband and high throughput, orbital-angular-momentum multiplexing at a high spectral efficiency and binary coding along large-angle bending channels for bit-error-free acoustic data transmission in an underwater environment are demonstrated. Very different from optical and/or electrical cable communications, acoustic waves can be simply and effectively coupled into remote meta-skin acoustic fibers from free space, which is technologically significant for long-haul and anti-interference communication. This work can enlighten many fluidic applications based on efficient waveguiding, such as in vivo ultrasound medical treatment and imaging.     

High-resolution underwater acoustic imaging with lens-based systems

In recent years, several sonars designed for high-resolution, short-range underwater imaging have been developed. These imaging systems use an acoustic lens to focus the incoming waves on an array of transducers. In this article we describe three prototype systems that use a line-focus or a point-focus lens and operate at a frequency of 300 kHz or 3 MHz. The line-focus lens produces two-dimensional (2D) intensity images, while the point-focus lens produces 3D intensity images. We present sample images taken from moving and stationary platforms, and discuss the techniques used for processing the acoustic backscatter data to reconstruct and visualize the scene. The images, particularly those taken with a point-focus lens, show a remarkable degree of detail. © 1997 John Wiley & Sons, Inc. Int J Imaging Syst Technol, 8, 377–385, 1997     

非声学公共建筑中的声品质

本文分析了在八种公共建筑类型中的声学专题研究结果, 包括火车站、商城、图书馆、开敞式办公室、足球场、游泳空间、用餐空间、及教堂, 旨在考查主观评价和客观指标之间的关系, 并且探索在非声学建筑中创造舒适的声环境的原则和框架。分析表明了声品质在这类非声学建筑中的重要性, 另外, 即使客观指标例如声压级和混响时间相同, 声舒适度亦可能完全不同。其它关键因素包括社会背景、心理调节、声音喜好、声学处理的接受程度, 声学与其他环境因素的相互作用、以及不满意的声品质可能造成的健康影响。     

An application of fast multipole method in analyzing acoustic filters

Abstract

The purpose of this study is to investigate the acoustic performance of mufflers. As a numerical scheme for analyzing an acoustic filter, the boundary element method is more suitable than are domain methods, such as the finite element method, which has to mesh the domain. However, the coefficient matrices established by the boundary element method are full and often non‐symmetrical. In order to decrease the computational time required, the fast multipole method has been applied. The fast multipole method, when compared with the boundary element method, reduces CPU time from an order of N² to Nlog^γ N, where N is the number of unknowns and γ is a constant. This study focused on the different geometries of plates within simple expansion acoustic filters. Numerical analysis demonstrates that the transmission loss at a particular frequency performance is better when employing a simple expansion acoustic filter with plates.     

水声透声材料发展概述

概述了水声透声材料的透声机理,声阻抗和透声层厚度为影响材料透声系数的主要因素。阐述了水声透声材料在声纳导流罩中的应用,并探讨了金属、橡胶和玻璃钢导流罩的优缺点。利用理论计算指导材料结构设计,从提高材料透声性能、材料密封性和耐海洋环境性三个方面综述了水声透声材料的研究进程。提出丰富、完善水下透声材料性能的计算模型,开发性能均衡的透声材料,以及研制全壳体声纳导流罩是水声透声材料研究和应用的发展方向。     

乐罩对剧院音质参量的影响分析

乐罩是有自然声演出功能剧场舞台表演区的重要组成部分,其作用是防止有限的自然声能被舞台吸收和逸散,并。文章分析了24座剧院加乐罩前后音质参量实测数据,研究了加乐罩前后音质参量的统计特性。加乐罩后的剧院,在混响时间、早期衰变时间、强度因子、舞台支持度等音质参量上均有显著的提升。     

《消声室的声学设计》

消声室是声学专业的实验室用房,它在电声学产品的声学性能检测和机电设备的噪声声功率级测量中得到广泛的应用。消声室的设计,应在遵循声学原理的基础上,处理好使用要求与实验室周围的声环境状况以及建设造价等方面的关系问题。文中结合消声室建设的工程实例,介绍了消声室设计中有关体积、体型、吸声、隔声等方面的技术问题。测量表明,建成的消声室在声学方面的各项指标均满足或优于国家标准的要求。     

热声发动机用声学放大器的改进研究

声学放大器是一种可显著提高热声发动机输出压力振幅和压比的装置,存在的主要问题是声功损失过大.通过理论研究,提出采用较大管径进一步提高声学放大器性能的方法,称为改进型声学放大器.实验结果表明:该声学放大器在大幅度提升输出压比的同时,没有明显降低发动机内的压比和破坏发动机内部声场,能使发动机工作在较高的品质状态.采用变负载法测量声功的实验结果也表明,改进型的声学放大器有效地解决了声功损失过大的问题.     

有限声束在固体板表面的声反射

采用将有限声束分解为一系列平面波的方法，对有限声束在液体－固体板－液体结构中的声反射问题进行了分析和计算。当有限声束以平面波反射系数相位为１８０°时的入射角入射时，在固体板表面反射的声束沿板表面存在显著的移动和展宽现象。本文的有关结果，对进一步研究有限声束在板状结构表面的声反射具有积极意义。     

Analysis of Approximate Inverses in Tomography I. Resolution Analysis of Common Inverses

The process of using physical data to produce images of important physical parameters is an inversion problem, and these are often called tomographic inverse problems when the arrangement of sources and receivers makes an analogy to x-ray tomographic methods used in medical imaging possible. Examples of these methods in geophysics include seismic tomography, ocean acoustic tomography, electrical resistance tomography, etc., and many other examples could be given in nondestructive evaluation and other applications. All these imaging methods have two stages: First, the data are operated upon in some fashion to produce the image of the desired physical quantity. Second, the resulting image must be evaluated in essentially the same timeframe as the image is being used as a diagnostic tool. If the resolution provided by the image is good enough, then a reliable diagnosis may ensue. If the resolution is not good enough, then a reliable diagnosis is probably not possible. But the first question in this second stage is always &;#x201C;How good is the resolution?&;#x201D; The concept of resolution operators and resolution matrices has permeated the geophysics literature since the work of Backus and Gilbert in the late 1960s. But measures of resolution have not always been computed as often as they should be because, for very data rich problems, these computations can actually be significantly more difficult/expensive than computing the image itself. It is the purpose of this paper and its companion (Part II) to show how resolution operators/matrices can be computed economically in almost all cases, and to provide a means of comparing the resolution characteristics of many of the common approximate inverse methods. Part I will introduce the main ideas and analyze the behavior of standard methods such as damped least-squares, truncated singular value decomposition, the adjoint method, backprojection formulas, etc. Part II will treat many of the standard iterative inversion methods including conjugate gradients, Lanczos, LSQR, etc.     

水声通信与水声网络的发展与应用

水声信道是迄今为止最为复杂的无线通信信道之一,其固有的时-空-频变以及窄带、高噪、强多途、长时延传输等特征,使水声通信和水声网络在性能上还难以满足人们在实际应用中的迫切需求,面临极大的技术挑战。介绍了水声通信与水声网络的特点和发展现状,分析了复杂多变的水声信道特点及水声通信所要解决的关键技术,包括调制、解调技术和信号检测技术;介绍了水声网络中的拓扑结构、多路访问、MAC协议和路由选择等方法。最后简要介绍美国Teledyne Benthos公司的水声Modem和美国海军的海网Seaweb网络及国内在此方面所取得的一些进展及应用前景。     

“水鸣天梯”声景观成因分析

基于周期台阶表面声阻抗理论,解释了"水鸣天梯"声景观的物理机制。首先在低频准平面波近似的情况下,利用阻抗转移公式得到了周期台阶单元表面声阻抗。数值解表明,在低频段台阶表面的声阻抗呈现纯容抗性,证实了表面波的存在。有限元软件仿真的结果与理论分析保持一致。应用表面波的性质,设计并进行了现场试验。试验数据分析表明:在台阶底部脚踏石阶或者发射脉冲声波,声波经过台阶表面作用,到达台阶顶部时只有低频部分的声能量得到了较大保留,与理论分析和模拟结果相一致,最终确定了正是周期台阶的表面波滤波效应使得脚踏声转变为悦耳的水滴声。