Acoustic Band Gaps in Three-Dimensional NaCl-Type Acoustic Crystals

We present the acoustic band gaps （ABGs） for a geometry of three-dimensional complex acoustic crystals： the NaCl-type structure. By using the super cell method based on the plane-wave expansion method （PWE）, we study the three configurations formed by water objects （either a sphere of different sizes or a cube） located at the vertices of simple cubic （SC） lattice and surrounded by mercury background. The numerical results show that ABGs larger than the original SC structure for all the three configurations can be obtained by adjusting the length-diameter ratio of adjacent objects but keeping the filling fraction （f = 0.25） of the unit cell unchanged. We also compare our results with that of 3D solid composites and find that the ABGs in liquid composites are insensitive to the shapes as that in the solid composites. We further prove that the decrease of the translation group symmetry is more efficient in creating the ABGs in 3D water-mercury systems.     

Acoustic cavitation

This article reviews the physics of cavitation generated by acoustic fields, covering the basic theoretical and experimental data needed for a proper understanding of the many effects of cavitation and their practical applications. The dynamics of bubble motion are developed, stressing the relation between stable and transient types of cavitation and their thresholds. Non-radial types of bubble motion are now known to initiate several important effects, including erosive action, and these are dealt with in detail. Direct verification of theories of bubble dynamics is obtained using high-speed cinematography. The most recent techniques and results are described, as are the highly-sophisticated experimental methods now being applied to the bubble-fields and aggregates, including the acoustic emission from stable and transient cavitation fields.     

Acoustic Flowmeter

Technical Physics - The design and metrological characteristics of an acoustic flowmeter of a gaseous or liquid substance flow have been considered. It has been shown that the device has a simple...     

Acoustic iridescence

An investigation has been undertaken into acoustic iridescence, exploring how a device can be constructed which alter sound waves, in a similar way to structures in nature that act on light to produce optical iridescence. The main construction had many thin perforated sheets spaced half a wavelength apart for a specified design frequency. The sheets create the necessary impedance discontinuities to create backscattered waves, which then interfere to create strongly reflected sound at certain frequencies. Predictions and measurements show a set of harmonics, evenly spaced in frequency, for which sound is reflected strongly. And the frequency of these harmonics increases as the angle of observation gets larger, mimicking the iridescence seen in natural optical systems. Similar to optical systems, the reflections become weaker for oblique angles of reflection. A second construction was briefly examined which exploited a metamaterial made from elements and inclusions which were much smaller than the wavelength. Boundary element method predictions confirmed the potential for creating acoustic iridescence from layers of such a material.     

Acoustic turbulence

Inertial range spectra of sound modes in several space dimensions are determined theoretically and by numerical experiments. The latter indicate a spectrum of shock waves as predicted by Kadomtsev and Petviashvili (1973).     

声学超构表面

声学超构表面是当前声学领域的研究热点,其是一种由人工微单元构成的超薄平面结构,由于其具备平面、超薄等独特物理特性及对声波的灵活调控能力,使得其在降噪隔振、隐身技术、非接触操控物体等诸多声学领域具有重要的应用前景。文章以反射型、吸收型、透射型声学超构表面为框架,深入介绍超构表面高效调控声波的物理机制并举例展示了其构建复杂声场的能力,包括任意点反射聚焦、低频完美吸声、自弯曲声束、螺旋声波以及声能量非对称传输。     

液体中的声处理应用和声空化工程

1引言 声波在好几个方面有它广泛不可替代的用途，像声通讯、声检测、控制声、声控制等。在几个方面的用途中有声处理一项，这时利用了声的能量。本文只讨论液体中的声处理应用。在长时期的实验室试验中它显示了，并且继续在显示，强大的潜力，但比较奇特的是，这么大量的实验室成果，只有很少数转化为生产力。本文强调转化为生产力的有利性和紧迫性。本文并且指出，液体中声处理的基本机理多是声空化，因此，分析研究在液体中大规模或生产化声处理时声空化的特征和行为，     

声学超构材料

2000年报道的具有局域共振带隙的声学材料是声学超构材料的前身,也是最早实现的声学超构材料.同光学、电磁超构材料一样,近年来声学超构材料也引起了许多学者的研究兴趣.文章介绍了到目前为止声学超构材料的主要研究进展,内容包括含共振单元的声学超构材料的负有效声学参数（包括质量密度、体模量等）的实现,以及不含共振单元的声学超构材料的一些有效声学参数的确定等,最后对声学超构材料的可能应用进行了简单展望.     

Extraordinary Acoustic Transmission in a Helmholtz Resonance Cavity-Constructed Acoustic Grating

We investigate both experimentally and numerically a complex structure,where 'face-to-face' Helmholtz resonance cavities(HRCs) are introduced to construct a one-dimensional acoustic grating.In this system,pairs of HRCs can intensely couple with each other in two forms:a bonding state and an anti-bonding state,analogous to the character of hydrogen molecule with two atoms due to the interference of wave functions of sound among the acoustic local-resonating structures.The bonding state is a 'bright' state that interferes with the Fabry-Perot resonance mode,thereby causing this state to break up into two modes as the splitting of the extraordinary acoustic transmission peak.On the contrary,the anti-bonding state is a 'dark' state in which the resonance mode remains entirely localized within the HRCs,and has no contribution to the acoustic transmission.     

An Acoustic Metamaterial Lens for Acoustic Point-to-Point Communication in Air

Acoustical Physics - Acoustic metamaterials have become a novel and effective way to control sound waves and design acoustic devices. In this study, we design a 3D acoustic metamaterial lens (AML)...     

Acoustic boundary layer

On the basis of the boundary-layer concept, a method is proposed for calculating the oscillation-velocity and temperature fields in a volume of arbitrary form, bounded by rigid walls and filled by a viscous heat-conducting fluid. It is shown that the potential part of the sound field may be determined as in an ideal non-heat-conducting fluid, while close to the wall there are not only potential waves but also eddy velocity waves and temperature waves moving out from the wall. A method of solving a broad class of problems is discussed in which the boundary conditions at a distorted surface may be replaced, without significant error, by conditions at a plane boundary.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 92–97, November, 1980.It remains to thank our colleagues in the acoustics faculty for participating in discussions of the work.     

Acoustic Gravity Vortices

The solitary dipole vortex solution is shown. to exist for the nonlinear equation describing low frequency acoustic gravity waves.     

声悬浮现象的研究

分析了声波在垂直谐振腔内使物体悬浮于空中的条件与位置,给出了运用声悬浮现象测量声速的方法并实测了声速.     

单向声传播结构研究

受到电子二极管整流效应的启发,对单向声传播结构展开了一系列的理论与实验研究：将超晶格结构与非线性声学材料组合构成了可实现声整流效应的声二极管结构;通过将反对称弹性结构引入到复合结构板来产生Lamb波的不对称模式转化,设计了可实现Lamb波单向传播的线性声学结构;基于声子晶体的部分禁带特性,在有限尺度声学系统中设计并实现了单向声学波导结构;设计并实现了由纯板与声栅构成的声单向传播结构,具有小尺寸与高效率的特点,且声波出射角度可调;基于声学梯度材料设计了可在极宽频带内实现不对称声传播的声学结构。     

Acoustic cavitation inception

This article presents a selective review of the subject of acoustic cavitation inception. Topics covered include cavitation threshold measurements, the role of dirt or pre-existing bubble nuclei in cavitation inception, radiation-induced acoustic cavitation, and a discussion of some unsolved problems such as cavitation thresholds in liquid helium and the effects of electric fields on thresholds.