声波的“单行道”——声二极管的理论与实验研究

作为第一个可实现电整流的器件,电子二极管的发明标志着现代电子学的诞生,并在全球范围内引发了各个领域内的革命,最终深刻地改变了我们的整个生活.声波作为一种重要的经典波,具有比电磁波更为悠久的研究历史及更为普遍的存在形式.因此,若能设计并实现一种可像电子二极管控制电流那样对声能量进行整流的声学器件,这将对声学的器件制造、实际应用乃至整个声学研究领域都产生重大影响,其学术意义及应用价值的重要性不言而喻.文章详细介绍了利用超晶格与非线性声学材料构成的声二极管的理论与实验方面的最新研究进展.     

Local resonant characteristics of a layered cylinder embedded in the elastic medium

Three kinds of resonant modes of a single layered circular elastic cylinder embedded in the elastic medium are analysed by considering the oscillation of the scatter＇s core, based on the fact that the core moves as a rigid body when the shell material is very compliant. The resonant frequencies of the single resonator acquired by our method are in good agreement with those calculated by the local interaction simulation approach （LISA） for the local resonant phononic crystal. Therefore, the local resonant characteristics of a single layered circular elastic cylinder can be used to evaluate the resonant frequencies of the phononic crystal. The effects of the geometrical and physical parameters of the shell and the core are also studied in details. This work is significant for designing the locally resonant phononic crystal based on the local resonant characteristics of the single resonator, and the resonant frequencies can be tuned by selecting the geometrical sizes and the materials.     

Homogenization of Three-Dimensional Periodic Solid-Solid Elastic Composites

We develop an approach to homogenize three-dimensional periodic solid-solid elastic composites with cubic lattice at low frequencies, by using plane wave expansion and perturbation theory with respect to the long wavelength limit. Based on the fact that the two shear waves propagating along lattice axis are degenerated, we derive formulae for effective velocities parallel and normal to the lattice axis, from which three independent effective elastic moduli are calculated, respectively. Theoretical results, which take into account the multiple scattering and the structure of the periodic medium, are in good agreement with the previous isotropic theory at high-symmetry directions.     

景云教授荣获美国声学学会林德希奖章

正2018年5月美国声学学会175届年会颁奖典礼上,美国北卡州立大学(NCSU)机械与航空系景云教授被授于林德希奖章(R.Bruce Lindsay Medal)。这是美国声学学会为表彰声学界有重要贡献的中青年学者而设立的荣誉奖章。自1942年设立该奖以来,景云教授是首位获得该奖章的由中国大陆成长的华人科学家。此前得该奖章后并成为声学名家的有如L.Beranek,D.M.Green,R.E.Apfel,L.R.Rabiner,M.F.Hamilton等人。景云教授十几年来在室内空间声场、声波方程数值计算、非线性声学、声学超材料以及超表面等研究     

Interaction of a bubble and a bubble cluster in an ultrasonic field

Using an appropriate approximation, we have formulated the interacting equation of multi-bubble motion for a system of a single bubble and a spherical bubble cluster. The behavior of the bubbles is observed in coupled and uncoupled states. The oscillation of bubbles inside the cluster is in a coupled state. The numerical simulation demonstrates that the secondary Bjerknes force can be influenced by the number density, initial radius, distance, driving frequency, and amplitude of ultrasound. However, if a bubble approaches a bubble cluster of the same initial radii, coupled oscillation would be induced and a repulsive force is evoked, which may be the reason why the bubble cluster can exist steadily. With the increment of the number density of the bubble cluster, a secondary Bjerknes force acting on the bubbles inside the cluster decreases due to the strong suppression of the coupled bubbles. It is shown that there may be an optimal number density for a bubble cluster which can generate an optimal cavitation effect in liquid for a stable driving ultrasound.     

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。     

Complete Band Gaps for Lamb Waves in Cubic Thin Plates with Periodically Placed Inclusions

We present a theoretical study for propagation of Lamb waves in cubic thin plates consisting of solid inclusions placed periodically in the host material The dispersion curves of Lamb waves propagating parallel to the surfaces of the plates are calculated based on the plane wave expansion method for triangular lattices. We realize the existence of full band gaps in the systems composed of W cylinders embedded in a Si matrix with filling ratio f=0.176 for different thickness ratios of h/a, where h is the plate thickness and a is the lattice spacing.     

Elastic Wave Propagation in Two-Dimensional Ordered and Weakly Disordered Phononic Crystals

Elastic wave propagation in two-dimensional solid-solid ordered and weakly disordered phononic crystals is studied by using finite-difference time-domain method. Theoretical results show that obvious band gaps in the ordered crystal could be found, while in the weakly disordered ones the band gaps could partially vanish. Furthermore,with increase of disorder, band gaps are destructed badly and prominently in the high frequency regime while slightly in the low regime. Comparing the energy transmission dependent on time, we find that the coda wave phenomenon is prominent in the ordered crystal while weakened in the weakly disordered ones, and the physical properties are discussed.     

弹性管中泡群内气泡的非线性声响应

将弹性管壁视为膜弹性结构,得到了管径较大弹性管中泡群内气泡弱非线性振动的动力学模型.利用逐级近似法对气泡的非线性共振频率、基频振动响应特性进行了理论分析.结果表明:气泡共振频率主要受泡群内气泡间相互作用的影响;气泡的非线性共振频率将发生偏移,其偏移量取决于共振响应振幅;气泡的声响应区存在最大频率值;在声响应的高频率区内声响应幅值有多值性.     

Investigation of a silicon-based one-dimensional phononic crystal plate via the super-cell plane wave expansion method

The super-cell plane wave expansion method is employed to calculate band structures for the design of a silicon-based one-dimensional phononic crystal plate with large absolute forbidden bands. In this method, a low impedance medium is introduced to replace the free stress boundary, which largely reduces the computational complexity. The dependence of band gaps on structural parameters is investigated in detail. To prove the validity of the super-cell plane wave expansion, the transmitted power spectra of the Lamb wave are calculated by using a finite element method. With the detailed computation, the band-gap of a one-dimensional plate can be designed as required with appropriate structural parameters, which provides a guide to the fabrication of a Lamb wave phononic crystal.