Double-frequency stroboscopic method for absolute calibration of vibration transducers

This paper describes a new stroboscopic technique for a more accurate optical determination of vibration amplitude for the purpose of calibrating vibration transducers; the apparatus is composed of standard equipment which has been adapted to purpose-developed circuitry.     

Resonance tracking and vibration stablilization for high power ultrasonic transducers

Resonant frequency shift and electrical impedance variation are common phenomena in the application of high power ultrasonic transducers, e.g. in focused ultrasound surgery and in cutting. They result in low power efficiency and unstable vibration amplitude. To solve this problem, a driving and measurement system has been developed to track the resonance of high power transducers and to stabilise their vibration velocity. This has the ability to monitor the operating and performance parameters of the ultrasonic transducers in real time. The configuration of the system, with its control algorithm implemented in LabVIEW (National Instruments, Newbury, UK), ensures flexibility to suit different transducers and load conditions. In addition, with different programs, it can be utilised as a high power impedance analyser or an instantaneous electrical power measurement system for frequencies in the MHz range. The effectiveness of this system has been demonstrated in detailed studies. With it, high transducer performance at high power can be achieved and monitored in real time.     

Radial vibration characteristics of spherical piezoelectric transducers

This paper presents the vibration characteristics of the radial mode in spherical piezoelectric transducers. The differential equations of piezoelectric radial motion have been derived in terms of radial displacement and electric potential. Applying mechanical and electrical boundary conditions yielded a characteristic equation for radial vibration. Theoretical calculations of the fundamental natural frequency have been compared with numerical and experimental results for transducers of several sizes, and have shown a good agreement. This paper discusses the dependence of natural frequencies on the radius and thickness of the piezoelectric spheres and the difference between piezoelectric and elastic resonances. From the results it has been concluded that the natural frequency was not affected for the first radial mode but was reduced by the piezoelectric phenomenon. It has also been concluded that the natural frequency of the first radial mode depended mostly on the radius rather than on the thickness of the sphere whereas the natural frequency of the second radial mode depended mostly on the thickness rather than the radius.     

径向复合压电陶瓷超声换能器的径向振动特性研究

对径向复合压电陶瓷超声换能器的径向振动特性进行了分析。该换能器由一个厚度极化的压电陶瓷实心圆盘和一个金属圆环在半径方向复合而成。论文首先研究了压电陶瓷圆盘及金属圆环的径向振动,推出了其径向振动的机电等效电路。在此基础上,利用换能器的径向边界条件,得出了径向复合压电陶瓷换能器的机电等效电路及其共振频率方程。探讨了换能器的共振频率和有效机电耦合系数与其几何尺寸之间的依赖关系。设计并实际制作了一些径向复合超声换能器,对其径向共振及反共振频率进行了测试,并利用有限元法进行了数值模拟。研究表明,利用文中理论得出的换能器的共振频率与实测值及数值模拟结果基本符合。     

Active-passive vibration absorber of beam-cart-seesaw system with piezoelectric transducers

In contrast with fully controllable systems, a super articulated mechanical system (SAMS) is a controlled underactuated mechanical system in which the dimensions of the configuration space exceed the dimensions of the control input space. The objectives of the research are to develop a novel SAMS model which is called beam-cart-seesaw system, and renovate a novel approach for achieving a high performance active-passive piezoelectric vibration absorber for such system. The system consists of two mobile carts, which are coupled via rack and pinion mechanics to two parallel tracks mounted on pneumatic rodless cylinders. One cart carries an elastic beam, and the other cart acts as a counterbalance. One adjustable counterweight mass is also installed underneath the seesaw to serve as a passive damping mechanism to absorb impact and shock energy. The motion and control of a Bernoulli-Euler beam subjected to the modified cart/seesaw system are analyzed first. Moreover, gray relational grade is utilized to investigate the sensitivity of tuning the active proportional-integral-derivative (PID) controller to achieve desired vibration suppression performance. Consequently, it is shown that the active-passive vibration absorber can not only provide passive damping, but can also enhance the active action authority. The proposed software/hardware platform can also be profitable for the standardization of laboratory equipment, as well as for the development of entertainment tools.     

基于双面阵CCD的动态目标振动测试研究

针对动态目标的多自由度振动测试问题,建立了基于双面阵CCD交汇测量技术的动态目标振动测试系统。通过两台相机拍摄目标靶振动图像,对所得图像进行图像处理后提取目标点像素位置信息,根据目标点像素始末位置变化解算出目标靶X、Y、Z三个维度的位移变化量。实验结果表明,测量精度约为0.1mm。测量系统具有结构紧凑、测量精度高、适用性强等特点。     

High-resolution time-average electronic holography for vibration measurement

Time-average electronic holography (also known as TV holography) is a widespread technique used in real-time, non-contact, whole-field vibration measurement. The quantitative interpretation of time-averaged fringe patterns is difficult because of speckle noise and of the decreasing visibility of higher-order Bessel fringes. Speckle noise may only be reduced during image acquisition, by multiple-frame averaging.The objective of this paper is to present two new methods allowing to obtain time-averaged fringe patterns presenting a high resolution and a high contrast between dark and bright fringes, as well as the associated quantitative interpretation. They are based on the elimination of the random phase component and on the reduction of the random intensity component of the time-averaged fringe pattern. The fringe patterns obtained by this method may be efficiently filtered in order to provide the precise locations of the Bessel-type fringes associated with the object vibration. The methods rely on the use of the simplest standard equipment, without any need for modulators or stroboscopic devices. Quantitative fringe interpretation is straightforward and based on the method of fringe skeletonizing and indexing. Fringe contrast is so high that skeletonizing may be done by simple thresholding.     

Nonparaxial multi-Gaussian beam models and measurement models for phased array transducers

A nonparaxial multi-Gaussian beam model is proposed in order to overcome the limitation that paraxial Gaussian beam models lose accuracy in simulating the beam steering behavior of phased array transducers. Using this nonparaxial multi-Gaussian beam model, the focusing and steering sound fields generated by an ultrasonic linear phased array transducer are calculated and compared with the corresponding results obtained by paraxial multi-Gaussian beam model and more exact Rayleigh-Sommerfeld integral model. In addition, with help of this novel nonparaxial method, an ultrasonic measurement model is provided to investigate the sensitivity of linear phased array transducers versus steering angles. Also the comparisons of model predictions with experimental results are presented to certify the accuracy of this provided measurement model.     

用于声-地震耦合探雷的激光测振技术研究进展北大核心CSCD

基于地雷独特机械特性和声-地震耦合原理的声-地震耦合探雷技术,在埋设地雷的安全有效探测方面具有广阔的应用前景,但针对实用工程探雷系统的研究还需要做大量工作。其中,声波耦合的地表振动信号非常微弱复杂,如何对其进行精确快速测量是一个关键难题。本文在声-地震耦合探雷技术原理的基础上,对地表振动的非接触激光测量技术(包括激光多普勒干涉技术、电子散斑干涉技术和激光自混合干涉技术)进行综述分析,并分析了电子剪切散斑干涉技术用于声-地震耦合探雷的可行性。     

Ultrasonic measurement of gas flow using electrostatic transducers

Ultrasonic gas flowmeters typically use narrowband piezoelectric transducer arrangements for interrogating the flow of gas in a pipe. In this work, the suitability of broadband electrostatic transducers operating at frequencies of up to 1 MHz for ultrasonic measurement of gas flow has been investigated. The transit time method of ultrasonic gas flow measurement was adopted and experiments were carried out using a laboratory test rig capable of producing a range of gas flowrates up to 17.5 m/s. The test rig also allowed easy interchange of different prototype flowmetering sections. Times of flight of ultrasonic waves interrogating the gas flow were measured using separate send/receive electrostatic transducer arrangements. Two flowmeter configurations were considered. The first interrogated the flow at 45 degrees in contra-propagating upstream and downstream directions. The second consisted of an up-stream interrogation at 45 degrees to the gas flow and an interrogation made normal to the flow direction. k factors correlating the fluid velocity along the ultrasonic path with the mean fluid velocity in the pipe were calculated using experimental ultrasonic data and anemometer measurements. All transducer configurations were numerically modelled using the computational fluid dynamics software package FLOTRAN (ANSYS Inc.). Theoretical gas flow velocities for both transducer arrangements were subsequently compared with experimental values and found to be in excellent agreement. A flow-dependent frequency shift of the received ultrasonic signals was also observed simultaneously with the transit time measurement.     

绝对重力测量中振动传感器振动补偿性能的分析

绝对重力测量的精度主要受振动噪声的限制.振动补偿是一种简单可行的振动噪声处理方法,它通过传感器探测振动噪声来对测量结果进行修正.现阶段对于不同传感器的振动补偿性能缺乏系统的分析与评估,仅停留在应用阶段.本文从理论出发分析了传感器性能对补偿效果的影响,并通过实验评估了不同振动环境下不同传感器的振动补偿性能.实验结果显示,采用低噪声地震计的振动补偿效果主要受带宽和量程的限制,在安静环境下可实现优于百微伽的单次测量标准差,但补偿效果随振动噪声高频成分的增强而降低,在动态环境下地震计则受量程限制而无法工作.采用加速度计的振动补偿效果主要受分辨率的限制,在复杂和动态环境下均可实现毫伽量级的单次测量标准差.本文为振动补偿技术应用于绝对重力测量提供了振动传感器选型的理论和实践依据,有望为振动补偿技术的进一步发展提供技术支撑.     

基于视觉的车辆与轨道相对振动状态测量方法研究

车辆与轨道相对振动状态对轨道线形测量有重要影响;分析了传统检测车辆与轨道相对振动状态测量方法的缺陷,提出一种基于视觉的车轨相对振动状态测量方法,以轨道建立世界坐标系,以车体建立车体坐标系。考虑相机镜头畸变,建立相机非线性模型,基于机器人手眼方法标定相机与车体,求解相机内外参数。依据车体运动姿态特征,推导基于双目机器视觉的车辆运动姿态偏移补偿计算方法;运用实验平台设计验证实验,通过计算所得的车体振动位移与真实值高度吻合,随着车速增加振动位移误差也随之增大,验证了该方法的正确性和可行性;提供一种车辆与轨道相对振动状态测量方法。     

Multiple self-mixing interferometry based on lock-in amplifier analysis for vibration measurement

Optical Review - In this paper, a novel phase demodulation method for multiple self-mixing interferometry (MSMI) is proposed, which can improve the resolution and accuracy of vibration measurement...     

Multiple self-mixing interferometry algorithm based on phase modulation for vibration measurement

A novel algorithm based on a phase modulation and demodulation technique for multiple self-mixing interferometry was proposed in this paper. This algorithm can measure nanoscale vibration in real time and enhance the measurement resolution of a multiple self-mixing interferometer twofold compared with that of a self-mixing interferometer. In this paper, the principles of the method were described in detail, and a phase equation for multiple self-mixing interferometry was derived. Experiments were confirmed by conducting a series of experiments with different amplitudes, different signal-to-noise ratios, and different vibration waveforms. The experimental results showed that the algorithm can rapidly demodulate vibration in real time and indicated good agreement between theory and experiment.     

一种采用双换能器和摆式结构的宽频振动能量采集器

针对悬臂梁振动能量采集器在大振幅振动下梁容易断裂的缺点,本文提出了一种基于摆式结构的具有宽频和倍频特性的振动能量采集器,该采集器由两个Terfenol-D/PMN-PT/Terfenol-D磁电换能器和嵌有六个磁铁的旋转摆构成.文中建立了摆式结构的摆动方程,分析了采集器的频率响应特性以及谐振时的机-磁-电转换特性,并对采集器输出电压波形进行了频谱分析.理论和实验研究表明:该采集器具有宽频和倍频特性,采集器样机在1 g(1 g=9.8 m/s~2)有效值加速度振动下,向下扫频时的半功率带宽达到4.8 Hz,且能在f=16.9 Hz的振动下获得3.569 mW的负载功率.利用双换能器以及采集器的倍频和宽频特性,能有效地提高低频时采集器的输出功率.     

基于声压-振速测量的单面声场分离技术

在近场声全息技术的基础上,研究了基于声压-质点振速测量的单面声场分离技术.分析了现有基于Fourier变换的单面声场分离技术中的奇异性问题,并应用波数域谱平均法提出了去除奇异性的修正声场分离公式.为改善分离效果,减小由于Fourier变换引起的卷绕误差等因素的影响,基于统计最优近场声全息提出了一种新的单面声场分离方法.通过仿真分析对各种单面声场分离方法做了比较,并用Microflown公司的声强探头做了基于声压-振速测量的单面声场分离实验研究,验证了提出的修正公式和基于统计最优单面声场分离方法的正确性和有效性. 关键词： 声场分离 近场声全息 统计最优 Fourier变换     

在线转子振动参数的光电检测

为了测量在线转子的振动信息,以半导体激光器为光源,以PSD(position sensitive detector)为探测器,基于光电三角测量法,建立了一套包括软、硬件在内的激光测振系统。通过对该系统的标定实验表明,实际位移与所测得的位移呈线性关系。在数据处理中,对所得到的复杂时域振动信号进行了离散傅里叶变换(DFT),从而在频率域获得了转子的振动频率和振幅信息。通过采用多线程高级编程技术,解决了数据处理时间、图像及数据显示、存储时间之间的冲突,实现了在线测量。经测试表明,该测振系统的测量频率分辨率可达到0.6Hz,振幅不确定度小于±10μm。     

The system of double-optical-path ESPI for the vibration measurement

In this paper, a system of double-optical-path electronic speckle pattern interferometry (ESPI) for measuring larger vibration is proposed. This system combines the conventional ESPI optical path for measuring out-of plane vibration and the de-sensitized optical path. It can be used to observe qualitatively and analyze quantitatively the vibration mode. At the same time, the phase unwrapping is avoided. The anti-disturbance capability of this system is high, so it can be used to analyze the vibration characteristics of complex and discontinuous structure in actual engineering.     

Layout optimization methodology of piezoelectric transducers in energy-recycling semi-active vibration control systems

An optimization methodology is proposed for the piezoelectric transducer (PZT) layout of an energy-recycling semi-active vibration control (ERSAVC) system for a space structure composed of trusses. Based on numerical optimization techniques, we intend to generate optimal location of PZTs under the constraint for the total length of PZTs. The design variables are set as the length of the PZT on each truss based on the concept of the ground structure approach. The transient problems of the mechanical and electrical vibrations based on the ERSAVC theory are considered as the equations of state. The objective is to minimize the integration of the square of all displacement over the whole analysis time domain. The sensitivity of the objective function is derived based on the adjoint variable method. Based on these formulations, an optimization algorithm is constructed using the fourth-order Runge–Kutta method and the method of moving asymptotes. Numerical examples are provided to illustrate the validity and utility of the proposed methodology. Using the proposed methodology, the optimal location of PZTs for the vibration suppression for multi-modal vibration is studied, which can be benchmark results of further study in the context of ERSAVC systems.