Harmonic motion detection in a vibrating scattering medium

Elasticity imaging is an emerging medical imaging modality that seeks to map the spatial distribution of tissue stiffness. Ultrasound radiation force excitation and motion tracking using pulse-echo ultrasound have been used in numerous methods. Dynamic radiation force is used in vibrometry to cause an object or tissue to vibrate, and the vibration amplitude and phase can be measured with exceptional accuracy. This paper presents a model that simulates harmonic motion detection in a vibrating scattering medium incorporating 3-D beam shapes for radiation force excitation and motion tracking. A parameterized analysis using this model provides a platform to optimize motion detection for vibrometry applications in tissue. An experimental method that produces a multifrequency radiation force is also presented. Experimental harmonic motion detection of simultaneous multifrequency vibration is demonstrated using a single transducer. This method can accurately detect motion with displacement amplitude as low as 100 to 200 nm in bovine muscle. Vibration phase can be measured within 10° or less. The experimental results validate the conclusions observed from the model and show multifrequency vibration induction and measurements can be performed simultaneously.     

共振频率可调式非线性压电振动能量收集器

振动能量回收技术能够将环境中的机械振动能转换成电能,进而为微功耗装置供电,具有良好的应用前景。设计了一种利用压电材料的新型振动能量收集器,该机电耦合结构由一对非对称压电悬臂梁组成,悬臂梁末端固定有永磁体,利用永磁体产生的非线性力,实现了悬臂梁共振频率与外界激振频率的匹配调节。提出了该结构的理论模型,借助Matlab/Simulink数值分析软件对理论模型进行了仿真分析,并通过实验进行了验证。实验结果表明外界激励加速度幅值为3 m/s~2的时,结构即能实现较大频带范围内的频率匹配调节,频带范围不低于6.5Hz,最大回收功率不低于2 mW。     

一种新型电涡流阻尼器及阻尼性能研究

基于电涡流原理提出一种新型的可用于航天器振动被动抑制的电涡流阻尼器。首先,依托数值仿真建立阻尼器的磁场和力学有限元分析模型,对阻尼器的性能进行分析计算。其次,在振动测试实验台上进行阻尼特性测试,获得了小位移0.1 mm、大位移1 mm下的1 Hz～50 Hz频率范围内正弦激励作用工况下的阻尼系数。然后根据Bouc-Wen滞回模型建立了阻尼器的力学模型,研究了负载、阻尼器结构、交变洛仑兹力之间的关系。研究结果表明这种新型的电涡流阻尼器在外载激励作用下能够输出与仿真结果较为接近的阻尼力,且阻尼系数随激励频率变化具有明显的规律性,根据仿真和实验结果建立的阻尼力力学模型可以很好地用于电涡流阻尼器的力学特性仿真分析。     

磁力非线性耦合的I-L组合压电梁俘能器发电性能试验研究EI北大核心CSCD

针对线性的压电振动俘能器俘能频带过窄,输出较低等问题,提出了一种磁力非线性耦合的I-L组合压电梁俘能器。俘能器由带永磁铁的I型压电梁和L型压电梁组成,可通过调节两永磁铁间的水平距离,得到不同的非线性磁力耦合效应。试验结果表明:存在最优电阻使压电俘能系统的输出功率最大;对比无磁力系统,磁力耦合的I-L组合压电梁俘能器共振频率发生了明显的偏移:I型压电梁向左偏移,L型压电梁向右偏移,拓宽了系统的俘能频带;当激励加速度为0.2 g水平距离为20 mm、激振频率为18.4 Hz时,俘能器最大可得到1.2 mW的输出功率。     

Miura折叠超材料在简谐激励下的振动响应

折叠超材料基于折叠结构发展而来,具有超常的物理性能。应用ADAMS分析典型的三种结构模型,在力和位移两种简谐激励下,不同折痕刚度对Miura折叠超材料振动响应的影响。结果表明,单自由度结构的Miura模型在两种激励下频率响应类似,通过改变折痕刚度可以改变其共振频率,达到很好的低频隔振效果。多自由度模型可以通过增加堆叠数量降低共振频率。为Miura折叠结构的隔振设计提供一定理论参考。     

新型永磁隔振器的隔振性能分析与实验研究

在超精密加工、IC制造、光学、高端的物理及化学试验中,隔振器已经成了许多设备的一个关键部件,隔离来自地面和设备内部的振动。随着稀土永磁材料的迅速发展,永磁隔振器已成为国内外研究的热点之一。本文将采用环形永磁体提出了一种新构型的永磁隔振器;根据环形永磁体的磁力和刚度的解析模型对隔振器的隔振性能进行参数化分析,确定了该隔振器磁环的结构参数。作为新型永磁隔振器的试验研究,搭建了永磁隔振试验台,通过理论计算和试验证实了该磁浮隔振器在其最大承载能力时具有良好的低频隔振性能。     

矩形永磁铁的磁力计算及其应用

负刚度结构可用于系统的低频隔振,依据等效磁荷法建立矩形永磁铁的磁力和刚度解析模型,得到实现负刚度的最优磁铁布置和充磁方向,并设计三磁体型准零刚度隔振系统。仿真结果表明,矩形磁铁磁力和刚度计算模型准确,三磁体型准零刚度隔振器在不影响载荷性能的前提下具有优越的低频隔振性能。     

砧骨激励式压电振子听力补偿性能实验

针对传统压电式人工中耳输出增益较小、工作频带窄的问题,提出利用压电叠堆型压电振子激振砧骨体来补偿听力。为验证该方案的可行性,搭建由送声器、测声探管、压电振子及激光测振仪等构成的颞骨实验台,对振子动态特性、听骨链在声激励下及压电振子激振下的动态特性进行了测量。通过对比分析镫骨在两种激励下的运动情况,研究压电振子的听力补偿情况。结果显示,该砧骨激励式压电振子在低功耗、低电压下,便能对听力损伤进行有效补偿。此外,该压电振子听力补偿时还具有高频性能优异的特点,一方面在同等驱动电压下,高频补偿能力更强,能激起高达130 dB鼓膜声激励对应的运动幅度;另一方面,对高频段听力补偿时,具有较高的清晰度。     

Force and Stiffness of Passive Magnetic Bearings Using Permanent Magnets. Part 2: Radial Magnetization

This paper deals with the calculation of the force and the stiffness between two ring permanent magnets whose polarization is radial. Such a configuration corresponds to a passive magnetic bearing. The magnetic force exerted between ring permanent magnets is determined by using the Coulombian model. The expressions obtained are semianalytical and we show that it is not possible to find an exact analytical expression of the force between two ring permanent magnets. Then, thanks to these semianalytical calculations, the ring dimensions are optimized in order to have a great force or a great stiffness. Moreover, we show that the relative position of the rings for which the force is the strongest depends on the air gap dimension. This result is new because the curvature effect is taken into account in this paper. We can say that such semianalytical expressions are more precise than the numerical evaluation of the magnetic forces obtained with the finite-element method. Moreover, semianalytical expressions have a low computational cost whereas the finite-element method has a high one. Thereby, as shown in this paper, such calculations allow an easy optimization of quadripolar lenses or devices using permanent magnets.      

高层结构附加轨道非线性能量阱减振性能研究

轨道非线性能量阱(Track Nonlinear Sink,轨道NES)是一类被动减振控制装置,通过附加质量块沿轨道运动提供非线性回复力,以达到降低主体结构响应的目的。对轨道NES的回复力和控制系统的运动方程进行了理论分析和公式推导。对附加于32自由度主体结构的轨道NES进行了参数优化,优化后的轨道NES减振性能良好,并对装置刚度的变化具有较高的鲁棒性,但对装置阻尼变化较敏感。基于此问题,提出了单边碰振轨道非线性能量阱(Single-sided Vibro-impact Track Nonlinear Energy Sink,SSVI轨道NES),并考察了SSVI轨道NES装置刚度和阻尼同时发生变化时的减振性能。结果表明SSVI轨道NES能够有效降低结构响应,并同时具有良好的NES刚度和阻尼鲁棒性。     

Iron saturation effects in PM AC motors

Iron saturation causes the lumped circuit parameters to vary with the point of operation. Experimental evidence shows that the field excitation voltage and the direct axis reactance are not affected significantly by the armature reaction. This can be attributed to the presence in the direct axis of the magnets whose thickness represents a large effective air gap. In the quadrature axis, instead, the contribution of the air gap to the reluctance is small. Therefore, the quadrature axis reactance depends strongly on both the quadrature and direct axis components of armature magnetomotive force. This suggests a simple, albeit approximate, approach for predicting the parameter variation with operating point. As a result, both the design and analysis of synchronous motors excited by permanent magnets (PM's) are facilitated.     

Vibration of micromachined circular piezoelectric diaphragms

Electrically and mechanically excited resonances in micromachined circular piezoelectric diaphragms have been investigated. The diaphragm structures were piezoelectric unimorphs consisting of Pb(Zr0.52,Ti0.48)O3 (PZT) films and thermally grown silicon oxide (SiO2) layers. For electrical excitation, ring-shaped interdigitated (IDT) electrodes formed on the top of the PZT layer were used to induce strain in the diaphragms. The diaphragm structures behaved much like circular membranes in which the membrane tension was approximately 206 N/m, at the fundamental modes. For higher modes, the resonance frequencies deviated from the theoretical values due to the finite stiffness of the diaphragms. Under mechanical drive, both symmetric and asymmetric modes were excited. However, for electrical excitation, the symmetric modes were dominant due to the symmetry of the driving IDT electrodes. At a pressure of 727 Torr, the quality factor was approximately 250, and this rose to 2000 at pressures below 1 Torr. When a forward bias was applied to the diaphragm, the membrane tension decreased, but under reverse biases the tension increased. However, because of repoling under reverse biases greater than the coercive field of the PZT film, the achievable increase in the membrane tension was limited. In the diaphragm structure, the nonlinear vibration was governed by geometric nonlinearity rather than material nonlinearity. In addition, evidence of non-180 degrees domain wall motion of the PZT layer in released diaphragms was observed.     

新型准零刚度果蔬运输隔振系统设计

目的 为避免果蔬在运输过程中因振动造成损伤,导致价值下降,基于准零刚度隔振技术,提出一种采用紧凑、高效的弹簧–滚轮–滚珠负刚度机构的新型果蔬运输隔振箱装置。方法 首先,基于弹簧–滚轮–滚珠负刚度机构与垂向正刚度弹簧并联的方式设计准零刚度果蔬运输隔振系统结构;其次,分析其静力学特性,推导该非线性隔振装置的刚度特性;最后,在果蔬运输系统模型运动微分方程基础上建立Simulink仿真模型,研究在C级路面激励下,该新型运输隔振系统的动态隔振特性。结果 研究结果表明,通过合理的结构参数设计,该隔振装置在平衡点附近将具有高静态刚度、低动态刚度的准零刚度特性。在C级路面激励下,该新型运输隔振系统的振动位移峰的峰值相较于对应线性系统的衰减约29.3%,加速度均方根值衰减约97.3%。结论 设计合理的新型果蔬运输系统的隔振效率优于对应的线性隔振系统的。     

点力和线力作用下的结构振动响应研究

建立了平板结构在点力载荷和线力载荷作用下振动响应的理论模型，应用该模型计算出简支平板在两种载荷作用下的振动响应，然后进行比较分析。通过实验研究了点力载荷与实际惯性激振器产生的线力载荷作用下简支平板振动频响函数的差别。研究表明，点力载荷和线力载荷作用下的振动响应有一定差别，线力作用的圆环直径越大，这种差别越大，且高频段较低频段表现更为明显。     

一种超声手术刀推挽激励换能器的研究

设计了一种超声手术刀用的新型推挽激励换能器。它是在夹心式单晶堆压电超声换能器的经典构造基础上,把原先激励一组压电陶瓷晶片堆的方式,改为同时施加反相激励的前后两组晶堆。利用有限元方法,对该推挽激励换能器进行模态分析和频率响应分析。在相同大小的电压激励下,相对单晶堆换能器,推挽激励换能器可以获得更高的工作带宽和机电耦合系数,提高了换能器的电声转换效率。按照仿真结果加工推挽激励换能器,实现良好的动力学和电学特性,满足设计要求。     

A feasibility study of a post-buckled beam for actuating helicopter trailing edge flap

Active trailing edge flaps (TEFs) are one of the most promising devices for helicopter vibration reduction. Smart actuators such as the piezoelectric stack actuators (PEAs) are used for TEF actuation. PEAs possess high energy density and have large force in dynamic condition but are limited to small displacements. In this investigation, we study a linear to rotary motion amplification mechanism (AM-2) based on a pinned–pinned post-buckled beam to actuate trailing edge flaps. A linear motion amplification mechanism is developed and coupled with AM-2 to amplify angular flap deflections. Experiments are conducted on bench top-test setup, and maximum flap angle deflections of the order of 12° are achieved in the static case. An aeroelastic analysis is performed and 91 % reduction in helicopter vibration is obtained with multiharmonic control inputs.     

半主动控制拉索的稳定性分析

研究拉索在支座运动激励下参激振动不稳定性的半主动最优控制问题。建立斜拉索的多自由度参激振动方程，根据动态规划原理确定最优控制律，再按照MR阻尼器的Bingham模型得到半主动最优控制力及其相应的实施条件，分析控制力有界性、控制时滞、系统观测误差等主要因素对于索参激不稳定性控制的影响。数值结果表明，半主动最优控制可较大程度地提高索参激稳定性，控制时滞超过一定阀值将导致索完全不稳定。     

电液四轴高频结构强度疲劳试验系统

电液激振器受传统的电液伺服阀频响特性的限制,其激振频率难以提高,采用2D阀替代传统伺服阀组成电液激振器的方案,该激振器通过增加阀芯的旋转速度来提高其激振频率,同时将该电液激振器应用于4轴高频结构试验系统。对试验系统的结构和工作原理进行了分析讨论,包括频率、幅值和相位的控制方法。基于系统的频响仿真分析,提出了4个作动器的同步控制策略,对理论分析进行实验验证。试验结果表明:该电液四轴强度疲劳试验系统能在40 Hz~200 Hz范围内对试验对象进行同步加载试验,其频率、幅值连续可控。     

高架轨道桥梁新型橡胶减振支座的减振效果分析

为减小列车在高架轨道桥梁上运行引起的环境振动,开发了一种新型橡胶减振支座。此新型支座采用高阻尼厚层橡胶块倾斜布置的设计方案,在实现竖向减振的同时还可以提供较大的横向水平刚度;为研究这种新型支座的减振效果,建立了上部质量块-橡胶减振支座-桥墩体系有限元模型,采用竖向扫频激振的方式对其减振效果进行数值模拟;设计了一系列工况对影响新型支座减振效果的因素进行分析。研究表明:激振力幅值对新型支座的振动插入损失无影响,但增大桥墩高度会导致新型支座的振动插入损失减小;当激振力幅值取140 kN、桥墩高度取6 m时,新型支座的振动插入损失为17.53 dB;在满足承载力的情况下,增大橡胶块的倾角、增大橡胶块中橡胶层总厚度、减少橡胶层数的划分,可以降低新型支座的压缩刚度,进而提高新型支座的减振效果。     

人字齿轮减振修形优化设计

通过理论齿面与修形曲面叠加设计人字齿轮修形齿面,结合TCA、LTCA技术,综合考虑轮齿刚度、轴向窜动及啮合冲击激励,建立人字齿轮啮合型弯-扭-轴-摆10自由度动力学模型。以LTE幅值、轴向力及振动加速度最小为目标,通过优化确定最佳修形齿面。研究表明,轴向窜动与修形可共同改善齿面载荷分布;转速增加啮合冲击激励较刚度激励、轴向窜动激励振动更明显,刚度激励与冲击激励为引起啮合线方向振动的主要原因,而轴向位移激励对啮合线方向振动无影响;轴向位移激励为引起轴向、扭摆方向振动的主要原因;修形可降低啮合冲击、轴向窜动量、轮齿刚度及刚度波动,能有效降低系统振动。