广义斯奈尔定律与声超表面*

给出了广义斯奈尔定律的相关理论推导,并总结回顾了之前的几种设计,包括声人工结构表面和几种声超表面的案例。首先,以人工结构表面为例,以解析推导为主,结合数值模拟和实验结果,证明了人工窄井结构的异常反射现象。随后,我们回顾了声超表面的设计方法,包括折叠空间式和亥姆赫兹腔式两种典型的结构化设计。最后,我们重点回顾了一种厚度仅为1/20波长的声超表面,用于设计超薄声扩散体,称为声超表面施罗德扩散体。传统的施罗德扩散体是40年前提出的建筑声学领域的经典设计,而我们提出的声超表面施罗德扩散体在中心频率具有同样优质的漫反射效果。另外,通过混合不同目标频率的超表面单元,可以设计宽带的超薄施罗德扩散体,其带宽接近于商业化的施罗德扩散体,这个例子充分展示了声超表面在实际场合的应用潜能。     

阶梯状声扩散体形体优化方法

应用时域有限差分法计算阶梯状声扩散体扩散系数,结合免疫遗传算法分别对周期排布的六阶和十二阶阶梯状声扩散体的形体进行优化。首先,验证了时域有限差分法计算声场的有效性,之后采用两种方式进行优化设计:第一种是直接对多周期重复排布的扩散体形体进行优化;第二种首先对单周期扩散体形体进行优化,再将该扩散体重复周期排布。结果显示:第一种优化方式能获得扩散性能更优的周期排布的扩散体。单周期扩散性能最优的扩散体重复一定周期后,其性能不会保持最优,相反,扩散性能并非最优的单周期扩散体重复一定周期后的扩散性能却优于前者;扩散体总长度一定条件下,增加扩散体的阶次、降低重复周期数,可有效提升扩散体的扩散性能。因此,直接对多周期重复排布的高阶次扩散体形体进行优化,能够获得扩散性能最优的周期重复排布的扩散体。      

编码超构表面实现双波束独立可重构

近年来,有源超构表面因其对电磁波的灵活、动态调控而备受关注.本文设计并分析了一种有源可编程超构表面单元,并探讨了其在双波束、多波束独立可重构方面的应用.理论分析了如何实现对称双波束、非对称双波束电磁波辐射以及多波束独立可重构,并对所设计的编码超构表面进行仿真分析和实验验证.全波仿真结果表明,超构表面具有较好的辐射性能,主瓣辐射方向与理论计算结果一致.作为实验验证,我们加工了样品并在标准微波暗室中进行了测试.实验测试与仿真分析结果吻合良好,均表明该超构表面在微波频率能够对双波束进行独立的动态调控,且波束方向性较好.因而,这种可编程超构表面有望进一步实现多通道信息传输,并在无线通信系统中具有良好的应用前景.     

微穿孔板复合对二次余数扩散结构扩散性能影响研究

扩散吸声结构(Diffsorber)能应用于室内外声品质的改善,具有很好的研究意义和应用前景。微穿孔复合QRD结构能显著提高低频吸声性能,但复合对扩散性能的影响未见报道。本论文对QRD结构及其与厚度为0.6mm,穿孔率为1%,2%,3%的微穿孔板复合结构的扩散性能进行测试,得出了相应的反射声能极坐标图和扩散系数。研究结果表明,微穿孔复合QRD结构在中低频特别在结构自身共振频率范围内具有良好的扩散性能,扩散系数在0.8到0.95之间,随着频率增加,复合结构的扩散性能有下降的趋势,同时由于微穿孔板的吸声性能,复合后结构的空间反射声能普遍降低5dB左右。     

二次余数扩散结构复合穿孔板扩散吸声研究

声学结构研究一直以来都是学术领域的研究热点。扩散吸声结构(Diffsorber)由于兼具扩散和吸声性能而具有很好的研究意义。本研究将具有良好扩散性能的二次余数扩散(Quedratic:residue diffusers,QRD)结构和具有良好共振吸声性能的穿孔板结构进行组合,依据标准AES-4id-2001对二次余数扩散结构及其与厚度为1 mm,穿孔率分别为3%,5%,8%的穿孔板复合后结构的扩散性能进行了实验研究,得到了相应的反射声能极坐标图和扩散系数。结果表明,复合结构在100 Hz至800 Hz的频率范围内仍具有良好的扩散性能;复合结构反射声能在穿孔板共振频率范围内有明显的下降(平均超过2 dB)。本研究可为扩散吸声结构的设计与研制提供依据。      

基于压电材料的薄膜声学超材料隔声性能研究

针对低频噪声的隔离问题,设计了一种基于压电材料的可调控薄膜声学超材料,该材料由压电质量块嵌入弹性薄膜制成.建立了材料的有限元分析模型,并且计算了材料的各阶特征频率与20—1200 Hz频段的传输损失曲线,并通过实验验证了有限元计算的真实性.计算结果表明:此声学超材料在20—1200 Hz频段内隔声性能良好,存在两个50 dB以上的隔声峰与一个可调式的隔声峰.通过分析简单结构的首阶共振模态并构建其等效模型,从理论上探究了结构参数对薄膜声学超材料隔声性能的影响,并通过有限元计算验证了其等效模型的正确性;综合分析材料的特征频率与传输损失曲线,进一步讨论了结构的隔声机理,分析结果表明,在特征频率处,薄膜的"拍动"会导致声波在其后的传播过程中干涉相消,实现声波的衰减;通过Fano共振理论,探究了各共振点处传输损失曲线特征不同的原因;压电质量块与外接电路组成LC振荡电路,在电路的共振频率处,压电材料的振动可以吸收声波的能量从而造成一个隔声峰,同时可以改变外接电路的参数来调整电路的共振频率,从而实现对隔声性能的调控.最后,探究了压电质量块偏心量对材料性能的影响,并通过有限元计算验证了材料隔声性能的可调性.研究结果为可调式薄膜声学超材料的设计提供了理论参考.     

基于薄膜编码超表面的宽频超薄声散射体

该文提出了一种基于薄膜编码超表面的宽频超薄声散射体。利用附加质量块的薄膜和空气腔组成的薄膜结构构建了反射声波相位差接近180°的两种共振单元。将两种共振单元按照一定的顺序进行排列,可以组成深亚波长尺寸下的声学超表面。所构建的声学超表面可以产生宽频有效的散射声场。通过有限元仿真软件对多个频率的近场散射声场分布、远场声指向性和扩散系数进行了仿真计算,仿真结果显示,该散射体可以高效地散射入射声波,并且散射效果在一定的频率范围内是宽频有效的。     

扩散吸声体的优化设计

由于扩散吸声体(Diffsorber)同时兼顾了扩散和吸声两方面的性能,在小房间的声学环境控制中有着特殊的功能。在比较成熟声吸收和声扩散理论的基础上,结合数论中的伪随机理论,提出利用吸声材料本身的声阻抗实现伪随机分布的新优化设计手段,并利用计算机编程实现,由此设计了多种不同吸声效果的扩散吸声体,以满足不同场合的需要。实验结果表明新方法的有效性。同时探讨了新型吸声扩散体的应用潜力。     

可形变光学超构表面及其动态调控

经过近10年的发展,超构表面作为一种新型的二维人工微纳结构,在光场特性调控方面展现出了巨大的研究潜力。但要实现小型化、集成化的超构表面光电子器件,还需要进一步发展具备动态调控功能的光学超构表面。本文综述了近年来发展的可形变超构表面的研究进展,简要概述了以纳米剪纸技术为基础的可形变超构表面的设计和实现方法,并重点介绍了其在相位、偏振、光学手性、非线性辐射等方面优异的调控性能及其应用。这种灵活的、易实现的可形变超构表面在光场动态调控方面具有独特优势,为设计和实现新型微纳光电子器件提供了新的策略,有望推动新兴的应变光电子学的发展。     

表面低配位原子对声子的散射机制

由于纳米结构具有极高的表体比,声子-表面散射机制对声子的热输运性质起到关键作用.提出了表面低配位原子对声子的散射机制,并且结合量子微扰理论与键序理论推导出该机制的散射率.由于散射率正比于材料的表体比,这种散射机制对声子输运的重要性随着纳米结构尺寸的减小而增大.散射率正比于声子频率的4次方,所以这种散射机制对高频声子的作用远远强于对低频声子的作用.基于声子玻尔兹曼输运方程,计算了硅纳米薄膜和硅纳米线的热导率,发现本文模型比传统的声子-边界散射模型更接近实验值.此发现不仅有助于理解声子-表面散射的物理机制,也有助于应用声子表面工程调控纳米结构的热输运性质.     

Ternary and quadriphase sequence diffusers

A room acoustic diffuser breaks up reflected wavefronts, and this can be achieved by presenting a spatially varying surface impedance. In hybrid surfaces, varying impedance is achieved by patches of absorption and reflection, giving reflection coefficients nominally of 0 and 1. These surfaces are hybrids, absorbing some of the incident sound while diffusing any reflected energy. A problem with planar hybrid surfaces is that specular energy is only removed by absorption. By exploiting interference, by reflecting waves out-of-phase with the specular energy, it is possible to diminish the specular energy further. This can be achieved by using a diffuser based on a ternary sequence that nominally has reflection coefficients of 0, -1, and +1. Ternary sequences are therefore a way of forming hybrid absorber-diffusers that achieve better scattering performance without additional absorption. This paper discusses methods for making ternary sequence diffusers, including giving sequence generation methods. It presents prediction results based on Fourier and boundary element method models to examine the performance. While ternary diffusers have better performance than unipolar binary diffusers at most frequencies, there are frequencies at which the performances are the same. This can be overcome by forming diffusers from four-level, quadriphase sequences.     

Application of perforated sheets to improve the efficiency of reactive profiled noise barriers

The scope of this paper is to study the performance of noise barriers treated with different diffusers with/without a perforated sheet. We investigated the barrier insertion loss using a 2D boundary element method (BEM). To obtain a better depth sequence, a Random Sequence Diffuser (RSD) was designed. The results clearly showed that employing a "RSD" instead of the most popular Schroeder diffusers (Quadratic Residue Diffuser and Primitive Root Diffuser) increased the acoustic performance. We also found that the diffuser performance improved by treating the diffuser with perforated sheets either on the top surface or inside the wells. The addition of these perforated sheets inside the "RSD" (barrier model "RPI2") improved the performance by 3.59 dB (A).     

Wall diffuser designs for acoustical renovation of small performing spaces

This paper investigates the material characteristics of diffusers for acoustical renovation of existing small performing spaces. Consideration is given to acoustical effects on sound fields through the practical cases of two performing halls: the Chamber Hall (450 seats) and the M-Theater (630 seats) in the Sejong Performing Arts Center, Seoul. The Chamber Hall was completely refurbished into a recital hall from its previous shape of a rectangular conference space. The saw-tooth shaped wall diffuser profile in the Chamber Hall was designed using glass-fiber reinforced concrete for mid-frequency sound diffusion. The M-Theater was renovated as a live and intimate space for dramatic performances with a design that included more seats on the upper floors and additional spaces above ceiling reflectors. The vertically-patterned diffuser profile with protruded cubic surfaces in the M-Theater was designed using glass-fiber reinforced gypsum for sound diffusion in the major speech frequency range. Designed diffuser profiles were evaluated for both halls by measurements of scattering and diffusion coefficients of the 1:10 scale model diffusers. The effects of diffusers in both halls were also investigated by covering the lateral walls close to the stages with reflective materials to control diffusive surfaces. As a result, spatial uniformity increased with diffusive wall profiles in both halls.     

Maximum length sequence and Bessel diffusers using active technologies

Active technologies can enable room acoustic diffusers to operate over a wider bandwidth than passive devices, by extending the bass response. Active impedance control can be used to generate surface impedance distributions which cause wavefront dispersion, as opposed to the more normal absorptive or pressure-cancelling target functions. This paper details the development of two new types of active diffusers which are difficult, if not impossible, to make as passive wide-band structures. The first type is a maximum length sequence diffuser where the well depths are designed to be frequency dependent to avoid the critical frequencies present in the passive device, and so achieve performance over a finite-bandwidth. The second is a Bessel diffuser, which exploits concepts developed for transducer arrays to form a hybrid absorber–diffuser. Details of the designs are given, and measurements of scattering and impedance used to show that the active diffusers are operating correctly over a bandwidth of about 100 Hz to 1.1 kHz. Boundary element method simulation is used to show how more application-realistic arrays of these devices would behave.     

Study on echo suppression effect and coloration due to periodic-type diffusers

An echo is one of the obstacles in halls and theatres. In order to suppress this undesirable echo, walls and ceilings have been often given absorptive surfaces which absorb sound energy or corrugated surfaces which provide wave diffusion. While it is not difficult to predict the degree of echo suppression effects in the case of absorptive surfaces, it is generally difficult to do that in the case of corrugated surfaces. In addition, if the surfaces have periodicity, unintended effects called coloration can distort tonal characteristics of the sound field. Thus, many acoustic designers would hesitate to employ this kind of periodic-type diffusers. However, there are some cases where it is necessary to suppress echoes without any energy loss. Periodic-type diffusers have the advantages of easy estimation of diffusion properties, simple method of design, and ready availability. In this study, a subjective experiment with simulated stimuli was carried out to clarify the echo suppression effect of the periodic-type diffusers from the viewpoint of reflected energy level. Although coloration interfered subjective judgments in some cases of the experiment, it is shown that the periodic-type diffusers have echo suppression effects if the coloration does not occur. This study is also devoted to discussion about causes and features of the coloration.     

随钻新型隔声体的声学性能研究*

近年来,随钻声波测井成为了一种新兴的勘探方式,但是在勘探过程中产生的钻铤波会影响地层信号的提取。如何能够更有效的提取地层信号,成为学者研究的重点课题。本文基于声子晶体理论设计了一种新型隔声体,相对于传统刻槽结构能够更好的压制钻铤波。首先基于周期结构理论,利用有限元软件COMSOL MUTIPHYSICS计算了不同刻槽结构的能带图,相比于传统刻槽结构,新型隔声体有更宽的带隙,说明新型刻槽结构可以更有效的阻隔钻铤波。接着在测井模型中对刻槽结构进行频响函数曲线的计算,验证了新型刻槽结构隔声效果在所计算频率范围内优于传统刻槽结构。然后分析了在能带计算和频响曲线计算下隔声效果最好的声源频率(17kHz和22kHz)时新型刻槽结构的STC(时间慢度相关法)处理对比,最后对比声源频率17kHz下新型刻槽结构和传统刻槽结构的STC信号处理,发现此声源频率时新型刻槽结构可以更好的提取地层折射纵波和横波。     

基于联合波叠加法的浅海信道下圆柱壳声辐射研究

针对浅海信道下弹性结构声辐射预报尚无高效可靠的研究方法,提出了一种浅海信道下弹性结构声辐射快速预报的联合波叠加法.该方法结合了浅海信道传输函数、多物理场耦合数值计算法和波叠加法理论,运用该方法可对浅海信道下弹性结构辐射声场进行快速预报.经数值法和解析解法验证后,从信道下辐射源、环境影响和辐射声场测量的角度研究分析了浅海信道下弹性圆柱壳的声辐射特性,阐释了进行浅海信道下结构声辐射研究的必要性.研究结果表明,仅在低频浅海信道下弹性结构可近似等效为点源,信道上下边界对声场产生显著的耦合影响,高频段的空间声场指向性分布尤为明显,垂直线列阵进行信道下结构辐射声功率测量时,测量结果受到信道环境边界和潜深的影响较大.     

Diffusion and sound absorption properties of the quadratic residue diffuser structure with perforated panel

Acoustic structure study always is the academic research interest. Diffusion ab?sorbing structure(DiflFsorber) has good research value because it has both diflFusion property and sound absorption property. Quadratic residue diffusers(QRD) structure which had good diffusion property was combined with the perforated panel which had good sound absorption property in this study. According to standard AES-4id-2001, the diffusion experiments were carried out to study QRD structure and ones composited with perforated-panels which had1 mm-thickness and perforated percentage of 3%, 5%, 8% respectively. The polar coordinate diagrams of different structure were analyzed to derive the diffusion coefficients. Results showed that the composite structure still had good diffusion performance in the frequency range from100 Hz to 800 Hz. The reflection sound energy of composite structure reduced obviously in the perforated panel resonance frequency range where there was about 2 dB reduction averagely.The study result can provide the reference for the design and development of diifsorber.