热超声倒装键合中换能杆末端多维振动的相关性研究

换能杆末端的振动情况对于超声键合机理的研究有着重要意义；换能杆末端的实际振动模式直接影响着芯片键合的质量。利用高精度非接触式激光多普勒测振仪采集了换能杆末端俯仰、水平、轴向振动速度，用相干函数方法分析了3个方向的相互耦合关系。分别对换能杆末端有未安装劈刀的情况做了比较，得出了在换能系统工作频率附近，换能杆末端轴向振速与水平、俯仰振速的相关程度。这对实际键合中，换能系统末端的劈刀安装长度的选择以及换能杆工作频率的选择有指导意义。     

连续动力系统时间序列的非线性检验

用相位随机化的替代数据方法，研究了连续混沌动力系统时间序列的非线性检验判定.研究发现，在不同的采样情况下，混沌时间序列的非线性特性检验有所差异，尤其对于过采样时间序列，往往会出现虚假的判断结果.针对过采样时间序列，最好采用能够反映非线性特征的参数，作为检验统计量进行检验判断. 关键词： 替代数据 关联维数 连续时间序列 非线性检验     

试样激励下轻敲模式原子力声显微镜的非线性动力学特性

利用Euler-Bernoulli梁理论和DMT针尖-样品作用力模型建立了试样激励下轻敲模式原子力声显微镜(AFAM)系统的动力学方程,并应用非线性动力学分析方法对AFAM微悬臂梁的振动特性进行研究。通过合理改变超声激励幅值、超声激励频率和针尖-样品初始间距等模型参数模拟得到微悬臂梁的超谐波、次谐波、准周期和混沌振动现象,采用时间序列、频谱、相空间、Poincare截面和Lyapunov指数等方法对不同非线性振动特性进行表征。通过分析不同模型参数条件下微悬臂梁针尖-样品作用力特性,探索了微悬臂梁不同非线性振动现象的产生机制。此外,研究了AFAM微悬臂梁运动的分岔特性,发现当超声激励幅值和针尖-样品初始间隙连续变化时,周期、准周期和混沌运动交替出现。研究结果对AFAM系统非线性动力学行为分析和混沌振动控制提供了理论参考。      

一种超混沌系统的加密特性分析

把欠采样的思想用于混沌保密通信系统的设计中，对Lorenz系统及一种典型的超混沌系统的时间序列进行了分析. 研究发现，加密系统的安全性不仅取决于系统维数，而且还与采样间隔的选取有关. 用VWK非线性检验方法和替代数据检验方法对上述混沌加密系统在不同采样间隔时的输出信号进行了检验. 关键词： 混沌加密 时间序列分析 VWK非线性检验 替代数据检验     

混沌时间序列全局预测新方法——连分式法

拓展了多项式逼近理论，利用连分式法建立了混沌时间序列非线性全局预测模型，此模型替代混沌序列的动力学方程，实现对其动力学特性分析，达到预测目的. 理论分析和仿真实验表明，连分式法能够有效预测一些混沌序列，该方法预测精度高，并且能得到显式的预测表达式. 关键词： 混沌时间序列 全局预测 连分式     

线性非高斯序列的替代数据检验新方法

替代数据法作为检验时间序列非线性和混沌的统计方法获得了广泛的应用.由于原替代数据法的零假设为线性高斯过程,可能把线性非高斯过程,特别是非最小相位过程误判为非线性.为了解决这一问题,提出并详细推导了基于功率谱等价的非最小相位序列求逆方法;结合基于高阶累积量的非最小相位自回归滑动平均模型辨识方法,提出了检验序列是否为线性非高斯过程的替代数据生成新算法.仿真算例表明,上述方法成功地克服了原替代数据法的不足. 关键词： 替代数据 非线性检验 非最小相位 功率谱等价     

非最小相位线性非高斯序列的替代数据检验

替代数据法作为检验时间序列非线性和混沌的统计方法获得了广泛应用.常用的替代数据法的零假设为“原序列来自(经过单调静态非线性变换的)平稳线性高斯随机过程”.拒绝此假设,并不能说明序列必然来自确定性的非线性动力系统,非最小相位的线性非高斯序列也会导致基于相位随机化的替代数据检验拒绝此假设 关键词： 替代数据 时间序列分析 非线性 非最小相位     

高功率超声脉冲激励下金属板的非线性振动现象研究

对高功率超声脉冲作用下金属板中的超谐波、次谐波、准次谐波以及混沌等非线性振动现象进行了实验和理论研究.在实验中,高功率超声换能器产生脉冲调制的高频振动激励金属板产生非线性振动,利用激光测振技术测量不同尺寸和不同固定方式下金属板复杂的非线性振动情况,并对其进行了时序分析、频谱分析以及相空间分析.根据实验条件,提出包含非线性接触阻尼的振动-碰撞动力学模型,用以研究强超声振动-碰撞作用下的板非线性振动机制,并进行了相应的理论计算.计算结果表明,超声换能器的变幅杆与金属板之间的间歇性高频碰撞作用是金属板强非线性振 关键词： 非线性板振动 强超声脉冲激发 振动-碰撞动力学     

摇摆条件下自然循环系统流量混沌脉动的检验与预测

利用替代数据法检验了摇摆条件下自然循环系统不规则复合型脉动的混沌特性, 并在此基础上进行混沌预测. 关联维数、最大Lyapunov指数等几何不变量计算结果表明不规则复合型脉动具有混沌特性, 但是由于计算结果受实验时间序列长度的限制和噪声的影响, 可能会出现错误的判断结果. 为了避免出现误判, 在提取流量脉动的非线性特征的同时, 需要用替代数据法进一步检验混沌特性是否来自于确定性的非线性系统. 本文用迭代的幅度调节Fourier 算法进行混沌检验, 在此基础上用加权一阶局域法进行混沌脉动的预测. 计算结果表明: 不规则复合型脉动是来自于确定性系统的混沌脉动, 加权一阶局域法对流量脉动进行混沌预测效果较好, 并提出动态预测方法. 关键词： 混沌时间序列 替代数据法 实时预测 两相流动不稳定性     

一种时间序列的弱非线性检验方法

时间序列的非线性是判定该时间序列具有混沌特性的必要条件.提出一种基于线性和非线性AR模型归一化多步预测误差比值的非线性检验量δ_NAR,采用替代数据法来检测时间序列中的弱非线性.以Lorenz时间序列为例,分析了估计非线性检验量δ_NAR时各相关参数对弱非线性检测性能的影响.通过混沌时间序列非线性检测试验,对4种混沌时间序列中的3种,非线性检验量δ_NAR都表现出比基于AIC模型选择准则的非线性检验量相似文献   

New technology for the design of advanced ultrasonic transducers for high-power applications

A new high-frequency ultrasonic transducer for wire bonding has been conceived, designed, prototyped and tested. In the design phase an advanced approach was used and established. The method is based on the two basic principles of modularity and iteration. The transducer is decomposed to its elementary components. For each component an initial design is obtained with finite elements method (FEM) simulations. The simulated ultrasonic modules are then built and characterized experimentally through laser-interferometry measurements and electrical resonance spectra. The comparison of simulation results with experimental data allows the parameters of FEM models to be iteratively adjusted and optimized. The achieved FEM simulations exhibit a remarkably high-predictive potential and allow full control on the vibration behavior of the ultrasonic modules and of the whole transducer. The new transducer is fixed on the wire bonder with a flange whose special geometry was calculated by means of FEM simulations. This flange allows the converter to be attached on the wire bonder not only in longitudinal nodes but also in radial nodes of the ultrasonic field excited in the horn. This leads to a nearly complete decoupling of the transducer to the wire bonder, which has not been previously obtained. The new approach to mount ultrasonic transducers on a welding-device is of major importance not only for wire bonding but also for all high-power ultrasound applications and has been patented.     

金属基复合结构粘接强度的非线性超声混频检测

采用非线性超声混频方法对金属基复合结构的粘接强度进行表征研究。以不同固化剂含量的铝合金丙烯酸酯粘接结构作为检测对象,基于非线性超声混频的共振条件及其作用机制,并结合粘接固化机理,开展了非线性超声混频实验。非线性超声混频模式选取两列横波生成和频纵波的方式,实验测量并计算不同基频周期数下的超声非线性参量。通过拉伸实验标定粘接结构的粘接强度,并采用扫描电镜分析拉伸断面微观结构,进而分析超声非线性参量与粘接强度的关系。从实验结果可以看出在不同周期的基频信号激励下,超声非线性参量随着粘接强度的增大均呈现出减小的趋势。研究表明非线性超声混频信号对金属基复合结构粘接强度的变化比较敏感,可以适用于类似结构件粘接强度状态弱化的表征。     

粘接界面特性的超声检测与评价

粘接界面特性的超声检测与评价既是物理学的前沿问题,又是经济建设和国防安全亟需解决的应用问题。高波阻介质下多层低波阻介质界面脱粘检测、滑移界面检测和粘接强度定量评价是粘接质量检测中遇到的三大难题。本文综述了课题组十余年来在攻坚三大难题方面的研究工作：建立了共振匹配理论,发明了六项关键技术并实现了技术集成,研制出全新概念的超声检测设备,解决了第一个难题;成功研制出横波直探头,用纵横波综合判断方法解决了第二个难题;对第三个难题,建立了粘接界面非线性弹簧模型,为利用非线性声学参量评价粘接界面奠定了理论基础,并探索性地利用统计性方法对粘接强度进行了预测,取得较好效果。     

超声换能器并联谐振频率的复合式跟踪方法研究

为了使超声换能器适应变化比较剧烈的负载,本文通过分析超声换能器在并联谐振频率附近工作时的频率特性和实际需求特点,利用变压器初级匹配方法得到了更好的频率特性,并对比了换能器空载和带负荷情况下的阻抗特性曲线,提出了复合式自动频率跟踪方法,空载时找到超声换能器最小电流的对应的频率点,加载过程中利用比例积分微分算法实现频率的快速跟踪。并对超声换能器在不同负载时的功率输出进行了实验,结果表明,复合式频率跟踪方法可以稳定地跟踪到超声换能器的并联谐振频率,能实现超声换能器的功率自调节,对提高换能器的工作效率和负荷适应能力具有实际的指导意义和应用价值。     

Theoretical analysis and experimental validation of radial cascaded composite ultrasonic transducer

A radial cascaded composite ultrasonic transducer is analyzed.The transducer consists of three short metal tubes and two radially polarized piezoelectric ceramic short tubes arranged alternately along the radial direction.The short metal tubes and the piezoelectric ceramic short tubes are connected in parallel electrically and in series mechanically,which can multiply the input sound power and sound intensity.Based on the theory of plane stress,the electro-mechanical equivalent circuit of radial vibration of the transducer is derived firstly.The resonance/anti-resonance frequency equation and the expression of the effective electromechanical coupling coefficient are obtained.Excellent electromechanical characteristics are determined by changing the radial geometric dimensions.Two prototypes of the transducers are designed and manufactured to support the analytical theory.It is concluded that the theoretical resonance/anti-resonance frequencies are consistent with the numerical and experimental results.When R_2 is at certain values,both the anti-resonance frequency and effective electromechanical coupling coefficient corresponding to the second mode have maximal values.The radial cascaded composite ultrasonic transducer is expected to be used in the fields of ultrasonic water treatment and underwater acoustics.     

Synthetic aperture focusing for defect reconstruction in anisotropic media

Ultrasonic inspection plays an important role in numerous industrial fields. One of the prominent tasks with respect to quantitative nondestructive evaluation is the determination of location, shape, size and orientation of defects. In this respect, the synthetic aperture focusing technique (SAFT) has been successfully applied to isotropic materials over the years. In anisotropic media, however, its application suffers from several phenomena, which are the direction dependence of the ultrasonic velocities, the beam skewing effect and the modified transducer radiation characteristics. In this article, a SAFT imaging algorithm is presented which fully accounts for the nature of wave radiation and propagation within anisotropic materials. For three-dimensional defect reconstruction, the spatial dependence of the ultrasonic group velocities as well as the radiation characteristics of the transducer are exploited--respective algorithms have been implemented for orthotropic material symmetry. Tests have been performed on unidirectional composite material.     

矩形辐射器压电多频超声换能器的研究

研究了一种具有多个共振频率的矩形辐射器夹心式超声换能器,换能器由圆柱形后盖板、压电陶瓷晶堆及矩形六面体辐射器前盖板组合而成。利用表观弹性法和一维近似理论给出了多频换能器横向及纵向理论共振频率方程。对一种特殊情况下的此类换能器进行了有限元及实验分析,给出了各自的频率输入导纳曲线。对理论和实验结果进行分析后表明,此类矩形辐射器夹心式超声换能器可以在不同的振动模态上工作,具有多个共振频率.     

Study on a novel omnidirectional ultrasonic cavitation removal system for Microcystis aeruginosa

Microcystis aeruginosa, as a typical alga, produces microcystin with strong liver toxicity, seriously endangering the liver health of human and animals. Inhibiting the bloom of the Microcystis aeruginosa in lakes becomes a significant and meaningful work. Ultrasonic cavitation is currently considered to be the most environmentally friendly and effective method for the removal of Microcystis aeruginosa. However, the commercialized ultrasonic algae removal systems require multi-Langevin transducers to achieve omnidirectional ultrasonic irradiation due to the single irradiation direction of the Langevin transducer, resulting in the complex design and high energy consumption. To achieve a low-cost, simple structure, and high-efficiency algae removal system, a novel omnidirectional ultrasonic cavitation removal system for Microcystis aeruginosa is proposed. The proposed system is major composed of a novel omnidirectional ultrasonic transducer, which generates the omnidirectional ultrasonic irradiation by its shaking-head motion coupled by two orthogonal bending vibration modes. Modal simulation, sound field simulation, and cavitation bubble radius simulation are first carried out to optimize the geometric sizes of the proposed transducer and verify the correctness of the omnidirectional ultrasonic irradiation principle. Then the vibration characteristics of the transducer prototype are measured by vibration tests and impedance tests. Finally, the feasibility and effectiveness of the proposed omnidirectional ultrasonic removal system for Microcystis aeruginosa are evaluated through the algae removal experiments. The experimental results exhibit that the algal cells damaged by ultrasonic irradiation from the proposed system do not have the ability to self-repair. In addition, the algal removal rates reached 55.41% and 72.97% after 30 min of ultrasonic treatment when the corresponding ultrasonic densities are 0.014 W/mL and 0.021 W/mL, respectively. The proposed omnidirectional ultrasonic algae removal system significantly simplifies the configuration and reduces energy consumption, presenting the potential promise of algae removal and environmental protection.     

Load characteristics of high power sandwich piezoelectric ultrasonic transducers

Based on the equivalent circuit theory, the load characteristics of high power piezoelectric ultrasonic sandwich transducers are studied. Two types of loads are studied. One is liquid load as in ultrasonic cleaning, and the other is solid load as in ultrasonic drilling and machining. The effect of load and structure of the transducer on the resonance frequency of the transducer is analyzed. It is shown that the effect of load on the resonance frequency of sandwich transducers with different structures is different. For liquid load as in ultrasonic cleaning, the effect of the load on the resonance frequency of the sandwich transducer with symmetrical structure is the largest. It is the smallest for the transducer with its displacement node in the back metal cylinder. For solid load as in ultrasonic drilling and machining, the effect of the load on the resonance frequency of the sandwich transducer with its displacement node in the front metal cylinder is the largest. It is also the smallest for the transducer with its displacement node in the back metal cylinder. On the other hand, for some applications, such as ultrasonic drilling, when the lateral dimension of the tool is much less than that of the transducer, its effect on the resonance frequency of the transducer is small. The conclusions are useful in designing vibrating systems for different ultrasonic applications.