Vibration characteristics of aluminum surface subjected to ultrasonic waves and their effect on wetting behavior of solder droplets

The vibration characteristics of an aluminum surface subjected to ultrasonic waves were investigated with a combination of numerical simulation and experimental testing. The wetting behavior of solder droplets on the vibrating aluminum surface was also examined. The results show that the vibration pattern of the aluminum surface is inhomogeneous. The amplitude of the aluminum surface exceeds the excitation amplitude in some zones, while the amplitude decreases nearly to zero in other zones. The distribution of the zero-amplitude zones is much less dependent on the strength of the vibration than on the location of the vibration source. The surface of the liquid solder vibrates at an ultrasonic frequency that is higher than the vibration source, and the amplitude of the liquid solder is almost twice that of the aluminum surface. The vibration of the surface of the base metal (liquid solder) correlates with the oxide film removal effect. Significant removal of the oxide film can be achieved within 2 s when the amplitude of the aluminum surface is higher than 5.4 μm or when the amplitude of the liquid solder surface is higher than 10.2 μm.     

The computation of dispersion relations for axisymmetric waveguides using the Scaled Boundary Finite Element Method

This paper addresses the computation of dispersion curves and mode shapes of elastic guided waves in axisymmetric waveguides. The approach is based on a Scaled Boundary Finite Element formulation, that has previously been presented for plate structures and general three-dimensional waveguides with complex cross-section. The formulation leads to a Hamiltonian eigenvalue problem for the computation of wavenumbers and displacement amplitudes, that can be solved very efficiently. In the axisymmetric representation, only the radial direction in a cylindrical coordinate system has to be discretized, while the circumferential direction as well as the direction of propagation are described analytically. It is demonstrated, how the computational costs can drastically be reduced by employing spectral elements of extremely high order. Additionally, an alternative formulation is presented, that leads to real coefficient matrices. It is discussed, how these two approaches affect the computational efficiency, depending on the elasticity matrix. In the case of solid cylinders, the singularity of the governing equations that occurs in the center of the cross-section is avoided by changing the quadrature scheme. Numerical examples show the applicability of the approach to homogeneous as well as layered structures with isotropic or anisotropic material behavior.     

A novel acoustic emission beamforming method with two uniform linear arrays on plate-like structures

A novel acoustic emission (AE) source localization approach based on beamforming with two uniform linear arrays is proposed, which can localize acoustic sources without accurate velocity, and is particularly suited for plate-like structures. Two uniform line arrays are distributed in the x-axis direction and y-axis direction. The accurate x and y coordinates of AE source are determined by the two arrays respectively. To verify the location accuracy and effectiveness of the proposed approach, the simulation of AE wave propagation in a steel plate based on the finite element method and the pencil-lead-broken experiment are conducted, and the AE signals obtained from the simulations and experiments are analyzed using the proposed method. Moreover, to study the ability of the proposed method more comprehensive, a plate of carbon fiber reinforced plastics is taken for the pencil-lead-broken test, and the AE source localization is also realized. The results indicate that the two uniform linear arrays can localize different sources accurately in two directions even though the localizing velocity is deviated from the real velocity, which demonstrates the effectiveness of the proposed method in AE source localization for plate-like structures.     

Assessing the relationship between the inter-rod coupling and the efficiency of piezocomposite high-intensity focused ultrasound transducers

The electroacoustic conversion efficiency of the ultrasonic transducer is a critical performance index for high-power applications. The material properties, volume fraction (VF) and aspect ratio (AR) are typically regarded as the design parameters of the piezocomposite transducer. We hypothesized that the spacing between piezoelectric rods was also a dominant factor. Therefore, the inter-rod coupling effects on the efficiency of 1–3 piezocomposite ultrasonic transducers were investigated in this study. The efficiencies of six flat and three curved 1.0 MHz PZT4 epoxy composite transducers with different geometric parameters were measured. Finite element transient analyses of the inter-rod electrical-mechanical coupling in the composites were carried out to explain the measured results. The experimental results showed that for 0.47 AR, the 79% VF transducers had lower efficiency than the 64% VF and 53% VF transducers. For 0.19 AR, the efficiency of the 59% VF transducer was not greater than the efficiency of the 39% VF transducer. Numerical analyses demonstrated that the positive peak voltage induced by the coupling of the side rods was more than twice the level induced by the coupling of the diagonal rods for any spacing. The diagonal coupling voltage peak did not change for spacings larger than 0.2 mm. Moreover, for spacings of 0.05 and 0.1 mm, the inter-rod coupling caused 24% and 20% waveform shifts of the driving voltage, respectively, while the 0.2 mm spacing coupling caused a 14% reduction in the amplitude of the driving voltage. As a result, the asymmetry of the driving voltage degraded the efficiency of the composite transducers and became more severe when the spacing was decreased. We concluded that the efficiency loss induced by inter-rod coupling as a function of spacing should be considered when designing piezocomposite transducers.     

Complex-valued fractional statistics for D-dimensional harmonic oscillators

A system of isotropic harmonic oscillators obeying the Polychronakos fractional statistics with a complex parameter in a space having the dimension D>1$D>1$ is studied. Temperature dependences of the thermodynamic functions are analyzed in different temperature domains. The nature of the observed phase transitions is clarified. Both numerical and analytical estimates for the critical temperature are made depending on the number of particles, space dimensionality, and statistics parameter. Approximate correspondence with some other fractional statistics types is established.     

Multiple Quantum Well in static magnetic field and intense laser pulses

The energy spectrum and dipole matrix elements of a multiple quantum well (MQW) system has been calculated numerically by solving the time-independent Schrödinger equation using finite difference method, in the presence of magnetic field. The effect of barrier width is also investigated. The energy difference between the levels of various minibands and the energy difference between various levels of the same miniband is calculated for different number of wells in the MQW. Finally, the dynamics of the system in short laser pulses has been calculated numerically by solving the time-dependent Schrödinger equation. The effect of magnetic field on the dynamics is clearly shown and explained.     

Ultrawide low frequency band gap of phononic crystal in nacreous composite material

The band structure of a nacreous composite material is studied by two proposed models, where an ultrawide low frequency band gap is observed. The first model (tension-shear chain model) with two phases including brick and mortar is investigated to describe the wave propagation in the nacreous composite material, and the dispersion relation is calculated by transfer matrix method and Bloch theorem. The results show that the frequency ranges of the pass bands are quite narrow, because a special tension-shear chain motion in the nacreous composite material is formed by some very slow modes. Furthermore, the second model (two-dimensional finite element model) is presented to investigate its band gap by a multi-level substructure scheme. Our findings will be of great value to the design and synthesis of vibration isolation materials in a wide and low frequency range. Finally, the transmission characteristics are calculated to verify the results.     

某空间望远镜相关跟踪系统摆镜随机振动分析

介绍了基础激励下机构随机振动响应的理论与分析方法.利用有限元分析软件ANSYS建立了某空间望远镜相关跟踪系统摆镜的有限元模型,并进行了随机振动响应分析.通过分析考察了其承受动力学环境的能力.对计算结果进行了分析.指出了现有结构中的薄弱环节,提出了改进方案,为摆镜的设计提供了重要参考依据.     

月基极紫外相机反射镜组件的设计

为了使月基极紫外相机反射镜组件在月球环境下具有良好的力学和热学稳定性,从而保证相机的成像质量,本文针对月基极紫外相机所处的严酷的力学和温度条件,设计了一种满足月球环境的反射镜组件结构.通过对反射镜组件有限元模型的重力分析、热载荷分析、动态刚度分析以及结构强度分析,结果表明反射镜组件的一阶谐振频率达到354 Hz,在1 g重力作用和ΔT=50℃均匀温变作用下镜面综合面形误差RMS值分别达到3.62 nm和2.46 nm,满足反射镜面形要求.最后,通过静力学面形检测、力学试验、温度适应性试验及成像分辨率测试,结果显示反射镜镜面面形精度RMS值优于14 nm,反射镜组件的设计满足总体指标,验证了该方案的合理性.     

光刻物镜波像差检测平台移相装置的研制

针对基于剪切干涉原理的光刻投影物镜波像差检测设备中相移测量的需求,设计了一种移相装置.该装置采用了桥式放大机构,获得了较大放大比和相对紧凑的结构.从原理上对桥式放大机构进行了分析和讨论,得到了输入位移与其放大比之间的函数关系,并得到了其关系曲线.经过非线性有限元分析,对该装置的变形、受力和模态特性进行了验证.验证结果满足检测平台移相要求.