音叉的共振频率与双臂质量的关系研究及其应用

通过对音叉振动系统的研究,分析了受迫振动系统振动振幅与驱动力频率的关系及音叉共振频率与双臂质量的关系,并用共振原理设计了振动式液体密度传感器.     

基于泛频振动的石英增强光声光谱测声器优化设计

为了进一步提高基于泛频振动的石英增强光声光谱测声器探测灵敏度,在一次泛频振动模式下采用一个比商用标准音叉外形尺寸大5倍的定制大音叉,并对其性能进行优化.通过理论和实验研究得出了音叉与激光的最佳作用位置,发现音叉的一次泛频振动有两个波腹点,且在距离音叉根部8 mm处,音叉振臂的振动幅度最大.微型声音谐振腔由三种不同内径的不锈钢毛细管加工而成,与音叉组成共轴配置石英增强光声光谱光谱测声器,用来进一步增强信号幅值.在最佳微型声音谐振腔配置下,获得了30倍的信号增益因子,有效提高了石英增强光声光谱光谱测声器的探测灵敏度.     

剪切力模式近场扫描光学显微镜的恒幅反馈控制方法研究

剪切力模式近场扫描光学显微镜(Near-field Scanning Optical Microscopy,NSOM) 的音叉探针间距控制系统中,用相位反馈控制和检测剪切力,同时采用比例＋积分（PI）技术实现对音叉探针振幅的反馈控制,使探针振幅在扫描过程中保持为恒定值.用相位信号作为探针与样品间距控制信号,分别在无振幅反馈和有振幅反馈两种情况下,以不同速率扫描得到标准CD_RW光盘光栅的两组图像,并进行了比较分析.实验表明,恒振幅反馈电路的引入有助于提高探针系统的响应速度和灵敏度,改善所得图像的质量及分辨率.     

光纤倏逝波型石英增强光声光谱技术

采用块状光学准直聚焦透镜组的传统石英增强光声光谱(QEPAS)技术存在体积难以缩减,结构稳定性不佳,无法适应空间狭小、振动复杂的特殊环境等缺点.基于此,将光纤倏逝波技术与QEPAS技术相结合,提出了一种新型微纳结构光纤QEPAS痕量气体检测技术.实验中,为了提高QEPAS系统信号幅值,优化了石英音叉与激光束的空间位置、激光波长调制深度,同时对比了两种不同共振频率的石英音叉,最终采用共振频率较低的30.720 kHz石英音叉作为声波探测元件,获得的检测极限为6.25×10~(-4)(体积分数),归一化噪声等效吸收系数为4.18×10~(-7)cm~(-1).W·Hz~(-1/2).     

音叉受迫振动与共振现象的研究

研究了在不同测试条件下音叉的受迫振动与共振的规律.实验结果表明:音叉的共振频率与音叉双臂质量分布有关,所加的质量块越靠近音叉的节点,共振频率变得越小;改变磁性阻尼的大小,阻尼越大,共振频率和幅度越小;当驱动线圈与接收线圈同时向音叉节点处移动时,音叉幅频特性曲线的共振幅度逐渐减小,但共振频率逐渐增大.如果保持驱动线圈位置不变,接收线圈向音叉节点处移动时,共振频率基本保持不变,而共振幅度越来越小.     

振转耦合振子实验研究

介绍一个非常有趣的物理演示实验——振转耦合振子实验.弹簧振子实际上是一个具有两个振动模式的振动系统,两振动模式之间存在着耦合,振动能量将从一种模式向另一模式转移.在共振条件下可以实现能量在两模式之间的来回完全转移.     

微探针纳米尺度振动测试的实验研究

微探针是扫描探针显微镜(SPM)的重要组成部件,其共振频率等振动特性直接影响系统的性能。给出了系统微探针共振频率的测试方法,对微探针在压电陶瓷驱动力作用下的受迫振动进行了有限元分析。提出了相位变化0.1°所对应的0.1nm位移分辨率的双频激光外差干涉光学测量系统,对微探针纳米尺度振动特性进行了测试对比实验,并对SPM标定样块进行了比对分析。实验结果验证了双频激光外差干涉测量方法的可行性和其应用价值。     

四激励二维正交复合夹心式压电超声换能器的设计

提出了一种四激励二维正交复合夹心式压电超声换能器,换能器由四组纵向极化压电陶瓷晶堆、一个中心耦合金属块和四个外部金属圆锥组成。基于二维耦合振动机理和机电类比原理,建立了换能器的等效电路模型并推导了其谐振频率方程。利用有限元软件仿真分析了四激励正交复合换能器的频响特性和振动特性,并与其单独一个方向振子的振动特性进行了对比。加工了反相和同相模态的换能器,利用阻抗分析仪和激光测振仪测试了其频率响应和二维四向纵振动输出特性,并进行了大功率二维四向超声乳化实验测试。理论、仿真和实验结果表明:换能器具有反相和同相两个纵向正交共振模态,在这两种共振模态下均可实现二维四向纵振动输出,且换能器两个正交方向振子的纵向振动具有相互耦合加强的作用;等效电路法和有限元法所得换能器的共振频率和有效机电耦合系数与实验测试结果吻合,通过与单激励正交复合夹心式压电超声换能器的有效机电耦合系数对比,发现该换能器具有更高的有效机电耦合系数。     

用计算机研究音叉共振频率和双臂质量的关系

介绍用计算机研究音叉受迫振动时,振幅与驱动力的频率关系,以及音叉双臂质量与共振频率的关系,这种方法与以往用示波器观察的方法相比更加精确和实用。     

矩形板高阶模式超声振动辐射器的研究

在耦合振动理论以及矩形截面细棒弯曲振动的基础上,本文对矩形薄板的弯曲振动进行了研究,推出了自由边界矩形薄板的弯曲振动频率方程,研究了薄板的振动模式及其与共振频率的关系.实验表明,矩形薄板弯曲振动共振频率的测量值与计算值符合很好.用共振式矩形薄板作为超声清洗等液体中超声应用技术的声波辐射器具有声场分布均匀,换能器频率调节容易,声波辐射面大等优点,是一种很有前途的新型超声源.     

表象变换和久期微扰理论在耦合杜芬方程中的应用

本文通过对耦合杜芬方程线性项的表象变换及非线性项的久期微扰理论的应用,将耦合杜芬方程转化为简正表象下的退耦合形式,由此可以很方便地得出耦合杜芬方程的解.为了验证该方法的正确性,设计了音叉耦合实验,观测到了振幅谱谱峰的劈裂以及"振滞回线"现象,这些实验结果都可以和之前所得的理论结果符合得很好.本文求解耦合非线性方程的方法,为灵活运用非线性理论提供一种方案,同时可以推广到光、电等耦合体系,对理解耦合体系的动力学行为具有一定的指导意义.     

Anti-phase synchronization of two coupled mechanical metronomes

This paper mainly investigates the anti-phase synchronization of two coupled mechanical metronomes not only by means of numerical simulations, but also by experimental tests. It is found that the attractor basin of anti-phase synchronization enlarges as the rolling friction increases. Furthermore, this paper studies the relationship between different initial conditions and synchronization types. The impacts of rolling friction on in-phase and anti-phase synchronization times are also discovered. Finally, in-phase and anti-phase synchronization conditions of non-identical metronomes are discussed. These results indicate the potential complexity of the dynamics of coupled metronomes.     

Free vibration characteristics of double-walled carbon nanotubes embedded in an elastic medium

In this Letter, a theoretical analysis of the resonant vibration of double-walled carbon nanotubes (DWCNTs) and the DWCNTs embedded in an elastic medium is presented based on Euler-Bernoulli beam model and Winkler spring model. The vibration modes of DWCNTs are quite different from those of single-walled carbon nanotubes (SWCNTs). The resonant vibrations of DWCNTs are found to have in-phase and anti-phase modes, in which the deflections of the inner and outer nanotubes occur in the same and opposite directions, respectively. For the vibration of DWCNTs with the same harmonic numbers, the resonant frequencies of anti-phase mode are larger than the ones of in-phase mode. Moreover, influence of the surrounding medium on the resonant vibrations is investigated using the Winkler spring model. The results show that surrounding medium makes a strong impact on the vibration frequencies of in-phase mode, but little on those of anti-phase mode.     

A METHOD OF IDENTIFYING INTERFACE CHARACTERISTIC FOR MACHINE TOOLS DESIGN

In order to develop the technology of calculating static and dynamic behavior of a new product during its design period without prototype, an identification method for calculating interface characteristic of mechanical structure system is presented. The paper discusses an optimum algorithm, in which the contact stiffness coefficients are taken as design variables, aiming at minimizing the sum of squares of eigenfrequency differences between finite element modes and their corresponding experimental modes, based on mode shape identification. The corresponding software has been developed. Using the identified parameters from an interface sample composed of one base and two columns, the eigenfrequency of mechanical structure system has been calculated and their accuracy has been verified by testing.     

Anti-phase synchronization and ergodicity in arrays of oscillators coupled by an elastic force

We have proposed a mechanism of interaction between two non-linear dissipative oscillators, leading to exact and robust anti-phase and in-phase synchronization. The system we have analyzed is a model for the Huygens’s two pendulum clocks system, as well as a model for synchronization mediated by an elastic media. Here, we extend these results to arrays, finite or infinite, of conservative pendula coupled by linear elastic forces. We show that, for two interacting pendula, this mechanism leads always to synchronized anti-phase small amplitude oscillations, and it is robust upon variation of the parameters. For three or more interacting pendula, this mechanism leads always to ergodic non-synchronized oscillations. In the continuum limit, the pattern of synchronization is described by a quasi-periodic longitudinal wave.     

An improved model for the classical Huygens׳ experiment on synchronization of pendulum clocks

This paper introduces a new model for the classical Huygens? experiment on synchronization of two pendulum clocks hanging from a wooden coupling structure. The dynamics of the coupling—a beam with supporting structure—is modelled in detail using the finite element method. The pendula are considered as single dof systems with local nonlinearities—modelling the escapement. Consequently, the resulting coupled model consists of a finite set of nonlinear ordinary differential equations. Then, the existence of synchronous motion in the system is analytically investigated. Furthermore, this model is used in order to obtain numerical results illustrating the possible limit behaviour of the system. Besides in-phase and anti-phase synchronization, other kinds of limit behaviour appear, namely quenching, beating death, and modulating behaviour, phenomena, which ‘Huygens did not see’.     

微型石英音叉陀螺模态特性的有限元分析

MEMS石英音叉陀螺是近年来发展起来的新型惯性器件。在石英音叉的早期设计阶段,为了提供可靠的设计方案,并缩短设计周期,应该对其进行分析模拟。音叉的结构参数至关重要,不仅会影响陀螺的敏感性,还会影响其检测精度和稳定性。本文以U形音叉为例,利用大型有限元分析软件ANSYS建立了微型石英音叉的实体模型,对其模态特性进行了分析和计算,分析了音叉几何尺寸对其谐振频率的影响,并提供了一组可供实际制作的音叉结构参数,大大缩短了设计周期。     

Pre-B?tzinger复合体的从簇到峰放电的同步转迁及分岔机制

Pre-Bötzinger复合体是兴奋性耦合的神经元网络,通过产生复杂的放电节律和节律模式的同步转迁参与调控呼吸节律.本文选用复杂簇和峰放电节律的单神经元数学模型构建复合体模型,仿真了与生物学实验相关的多类同步节律模式及其复杂转迁历程,并利用快慢变量分离揭示了相应的分岔机制.当初值相同时,随着兴奋性耦合强度的增加,复合体模型依次表现出完全同步的“fold/homoclinic”,“subHopf/subHopf”簇放电和周期1峰放电.当初值不同时,随耦合强度增加,表现为由“fold/homoclinic”,到“fold/fold limit cycle”、到“subHopf/subHopf”与“fold/fold limit cycle”的混合簇放电、再到“subHopf/subHopf”簇放电的相位同步转迁,最后到反相同步周期1峰放电.完全(同相)同步和反相同步的周期1节律表现出了不同分岔机制.反相峰同步行为给出了与强兴奋性耦合容易诱发同相同步这一传统观念不同的新示例.研究结果给出了preBötzinger复合体的从簇到峰放电节律的同步转迁规律及复杂分岔机制,反常同步行为丰富了非线性动力学的内涵.     

Theoretical investigation of helix distortion and dielectric spectrum of antiferroelectric liquid crystals

Landau-Ginzburg equation is utilized to investigate the dielectric spectrum of an antiferroelectric liquid crystal (AFLC). Two collective modes, one associated with the in-phase motion at the low frequency side and the other related with the anti-phase motion at the high frequency side, are discussed in details utilizing the concept of bulk free energy of the material in terms of the pair interactions of two adjacent Smectic layers. The phenomenon of helix distortion related to the in-phase motion is observed theoretically based on the interlayer interactions of the AFLC system. The anti-phase mode related to the degree of the antiferroelectric ordering is also an important phenomenon depending on the layer-to-layer interactions. Finally we have theoretically obtained the critical field for helix unwinding with the model proposed by de Gennes.     

Synchronized Anti-Phase and In-Phase Oscillations of Intracellular Calcium Ions in Two Coupled Hepatocytes System

We study the dynamic behaviour of two intracellufar calcium oscillators that are coupled through gap junctions both to Ca^2＋ and inositol（1,4,5）-trisphosphate （IP3）. It is found that synchronized anti-phase and in-phase oscillations of cytoplasmic cadcium coexist in parameters space. Especially, synchronized anti-phase oscillations only occur near the onset of a Hopf bifurcation point when the velocity of IP3 synthesis is increased. In addition, two kinds of coupling effects, i.e., the diffusions of Ca^2＋ and IP3 among cells on synchronous behaviour, are considered. We fnd that small coupling of Ca^2＋ and large coupling of IP3 facilitate the emergence of synchronized anti-phase oscillations. However, the result is contrary for the synchronized in-phase case. Our findings may provide a qualitative understanding about the mechanism of synchronous behaviour of intercellular calcium signalling.