圆筒状超磁致伸缩致动器磁场研究与仿真

为设计圆筒状超磁致伸缩致动器(GMA),采用基于磁路的方法对圆筒状超磁致伸缩材料(GMM)内的磁场强度进行计算,基于Maxwell软件建立了圆筒状GMA的3D模型并对磁路结构中各部件尺寸及GMA筒内构件的磁导率对磁场的影响进行了仿真研究。结果表明:在闭合的磁路结构中,对于给定的线圈匝数和激励电流,GMM筒中磁场强度大小受GMM筒轴向长度影响较大且为负相关。磁场均匀性方面,影响较大的是穿过圆筒状GMA构件的磁导率和导磁环轴向长度,二者均与磁场不均匀度正相关。     

超磁致伸缩微位移致动器的研究

 基于超磁致伸缩材料的磁致伸缩特性设计了一种用于微位移驱动的致动器．分析了致动器工作磁场的组成，计算了线圈的工作电流，并以此为依据设计了稳流电源．分析结果表明，设计的稳流电源满足工作要求；线圈提供的工作磁场能够保证超磁致伸缩棒工作在线性区域。     

超磁致伸缩激振器的结构优化及动态性能研究

超磁致伸缩激振器的结构决定其动态性能。为了提高激振器的动态性能,其驱动线圈采用减少匝数、增加线径、大电流驱动的设计方案。采用叠片式GMM棒,计算了它的几何参数,并选取了最佳的预压应力和磁场强度;设计驱动线圈时考虑了温度的影响,优化了它的几何尺寸和磁路设计,驱动磁场由方波信号叠加直流分量产生;建立了激振器的数学模型,用MATLAB进行了仿真,分析了其阶跃响应。实验表明,激振器的动态性能显著提高,应用效果到达了振动时效的要求。研究结果为超磁致伸缩激振器的结构优化与设计提供参考依据,具有重要的工程应用价值。     

伺服阀用超磁致伸缩致动器结构设计及输出位移建模

针对传统永磁偏置式超磁致伸缩致动器轴向偏置磁场均匀性较差的问题,设计了一种具有分布式永磁体偏置结构的阀用超磁致伸缩致动器;采用控制变量的方法,在限定超磁致伸缩致动器结构尺寸的条件下,通过改变超磁致伸缩棒的段数,对致动器偏置磁场进行仿真分析,并确定了最佳分布结构;基于磁阻理论、J-A模型、二次畴转模型及振动理论知识建立了阀用超磁致伸缩致动器的输出位移模型,并通过Matlab中lsim函数对致动器的阶跃响应及谐波响应进行了数值求解;为验证结构设计的合理性和模型的准确性,搭建了该致动器的试验系统,并进行了阶跃响应及谐波响应试验;结果表明:所设计的阀用超磁致伸缩致动器阶跃响应时间可达2.37 ms,在20 Hz到200 Hz的驱动频率范围内,试验结果与模型计算结果基本吻合,证明了模型的准确性。     

GMA的温度特性分析及热形变被动补偿方法研究

利用超磁致伸缩材料的磁致伸缩效应特性制成的磁致伸缩智能构件,位移输出精度可达亚微米级,这为精密与超精密加工领域提供了新的驱动解决方案,这种精密微驱动过程是依靠智能材料的功能性实现的。然而,在磁致伸缩智能构件工作过程中,线圈的焦耳热损耗、材料磁滞与涡流损耗等因素会导致其温度升高,并伴随着材料出现热变形、磁致伸缩系数不稳定等问题,从而严重影响系统的输出性能。为降低温升对磁致伸缩智能构件工作性能的影响,对超磁致伸缩致动器的温度变化特性进行了深入分析,提出一种热形变被动补偿机构,完成了具有热形变自补偿功能的超磁致伸缩致动器设计。实验结果表明,磁致伸缩致动器的主要发热形式和发热源,取决于激励电流形式、工作频率;所设计的超磁致伸缩致动器在工作过程中能够对热形变自动进行补偿。研究结果为提高磁致伸缩智能构件在精密与超精密驱动领域应用过程中的工作精度提供了一种途径。     

高精密厂房中高精密平台控制仿真模拟

为进一步提高高精密厂房中平台的隔振效果,在平台控制中考虑超磁致伸缩作动器的非线性特性对多自由度平台混合控制系统产生一定的制约作用,因此将四个超磁致伸缩作动器模型植入混合控制系统进行设计。首先建立一个以空气弹簧和超磁致伸缩作动器为基本元件的多自由度微振动混合控制系统,然后利用Jiles-Atherton模型的概念建立超磁致伸缩作动器的非线性及其逆补偿模型,并将所建立的作动器模型与多自由度微振动控制系统结合。最后对基于作动器模型的混合控制系统与被动控制系统下的高精密平台响应进行对比分析,取得较好的控制效果,为其在实际工程应用中提供可靠的理论依据。     

超磁致仲缩材料在心血管支架加工中微进给补偿控制中的研究

基于超磁致伸缩材料特性对微位移进给进行研究,设计了磁致伸缩致动器应用于心血管支架的加工,建立了致动器的传递函数模型。同时针对超磁致伸缩材料受温度,预紧力等因素影响对位移输出产生较大偏差,设计了PID调节器,并对磁致伸缩致动器控制系统给出了基于MATLAB的仿真,并在此基础上进行了离散化,得到了数字控制系统,并应用到实际中,并对实际输出位移进行对比。经过PID闭环控制调剂后,位移输出有了明显的稳定。     

超磁致伸缩驱动器磁滞非线性数值模拟研究

针对超磁致伸缩驱动器(giant magnetostrictive actuator,GMA)具有磁滞非线性现象,以经典Jiles-Atherton模型为基础,建立了包含偏置磁场强度和预压应力的GMA磁滞非线性模型,进行了数值仿真分析,得到了偏置磁场强度和预压应力对GMA磁化强度曲线和磁致伸缩应变曲线的影响规律。结果表明,偏置磁场强度对磁化强度曲线和磁致伸缩应变曲线的形状影响较大,调整偏置磁场强度的大小,可改变磁化强度曲线的线性区间,并能抑制或消除磁致伸缩应变曲线的倍频效应;预压应力对磁化强度曲线和磁致伸缩应变曲线的形状影响较小,施加不同的预压应力,可改变磁化强度曲线和磁致伸缩应变曲线的变化率。这与现有试验得到的结论相吻合,验证了所建磁滞非线性模型的合理性。     

柱棒式超磁致伸缩能量收集器的设计与实验

为了能够利用自然界中的振动能量,弥补传统微器件供能方式的不足。设计制作了一种以超磁致伸缩材料(GMM)为基础的振动能量收集装置,并通过实验加以验证其能量收集特性;首先,通过对超磁致伸缩材料物理特性的分析,进行了能量收集装置理论建模与仿真分析;然后,根据仿真分析的结果设计了一套柱棒式的超磁致伸缩能量收集器;最后,通过搭建实验平台进行了效果验证。实验结果表明:当输入激振信号频率f_n不变,振动能量收集装置输出电压峰-峰值和输入振动信号的幅值F_m成正比;当输入振动信号幅值F_m不变,振动能量收集装置输出电压峰-峰值和输入激振信号的频率fn成正比;在激振应力最大值为2.54 MPa、频率100 Hz的正弦激振条件下,感应线圈100匝的实验条件下,超磁致伸缩振动能量收集器输出电动势峰-峰值为136.4 mV,与理论值(156 mV)符合较好,且波形一致。     

超磁致伸缩作动器非线性模型辨识研究

准确辨识超磁致伸缩作动器非线性模型参数是位移精确控制的必要条件,针对标准粒子群(PSO)算法存在早熟收敛及迭代后期易陷入局部最优的不足,提出一种可动态调整惯性权重、学习因子及带遗传变异的改进型粒子群(IPSO)辨识算法,该算法可平衡全局和局部搜索能力,提高收敛速度和辨识精度,并将该算法应用于超磁致伸缩作动器非线性模型的参数辨识研究。结果表明:该算法能有效可靠地辨识超磁致伸缩作动器非线性模型参数,计算值和实验的吻合程度较高,并且具有一定的抑噪能力。     

Capacitance of High-Voltage Coaxial Cable in Plasma Immersion Ion Implantation

［1］J.R.Conrad, J.I.Radtke, R.A.Dodd, F.J.Worzala and N.C.Tran: J. Appl. Phys., 1987, 62, 4591. ［2］P.K.Chu, S.Qin, C.Chan, N.W.Cheung and L.A.Larson: Mater. Sci. Eng.: Reports, 1996, R17(6-7), 207. ［3］P.K.Chu, B.Y.Tang, Y.C.Cheng and P.K.Ko: Rev.Sci. Instrum, 1997, 68, 1886. ［4］X.B.Tian, B.Y.Tang and P.K.Chu: J. Appl. Phys.,1999, 86, 3567. ［5］M.M.Shamim, J.T.Scheuer, R.P.Fetherston and J.R.Conrad: J. Appl. Phys., 1991, 70, 4756. ［6］M.P.J.Gaudreau, P.E.Jeffrey, M.A.Kempkes, T.J.Hawkey and J.M.Mulvaney: J. Vac. Sci. Technol.,1999, B17, 888. ［7］I.Langmuir and K.Blodgett: Phys. Rev., 1924, 24, 49. ［8］R.A.Stewart and M.A.Lieberman: J. Appl. Phys.,1991, 70, 3481.     

A simple dynamic model for eddy currents in a magnetic actuator

This paper presents a simple dynamic model of eddy currents in a magnetic actuator. The model is based on the application of Maxwell's equations to a homogeneous ferromagnetic conductive material. The resulting diffusion equation is solved in two dimensions for a cross-sectional cut through a rectangular bar; boundary conditions are imposed by a sinusoidally varying actuator coil current. The utility of the new modeling approach is illustrated by predicting the dynamic performance of a magnetic bearing actuator. The predictions are found to be in good agreement with measured values. The model provides a new and convenient method of modeling the relationships among voltage, current, force, and flux in magnetic circuits containing eddy currents     

基于磁化机理的超磁致伸缩执行器磁滞模型

通过分析超磁致伸缩材料磁畴在外加磁场作用下的运动规律,建立了超磁致伸缩执行器基于磁化机理的磁滞模型。该模型结合执行器的工作条件,充分考虑了材料的非线性和滞回特性。模型包括磁致伸缩和磁化两个子模型,磁致伸缩模型描述了材料应变λ跟磁化强度M之间的关系;磁化模型描述了有效磁场Heff、无磁滞磁化Man、可逆磁化Mrev、不可逆磁化Mirr、总磁化强度M之间的关系。通过对实验测试结果进行分析,验证了模型能准确描述输入电流I与输出应变λ之间的关系。     

Numerical simulations of an electromagnetic acoustictransducer-receiver system for NDT applications

The development of a multistage numerical model of an electromagnetic acoustic transducer (EMAT), with particular emphasis on an EMAT receiver, is presented. The model includes five separate modeling states: static magnetic field simulation of an electromagnet; pulsed eddy current distribution of a generic meander-line coil suspended over a conducting specimen; Lorentz force distribution due to the interaction of the static magnetic field with the eddy current distributions; acoustic wave generation and propagation based on the dynamic Lorentz forces; and acoustic wave detection by an EMAT receiver. In particular, it is shown how the transient particle displacement fields are converted into an induced voltage response as part of the EMAT receiver system. Numerical simulations show that the voltage response is dependent on the wire spacing of the receiver coil     

Designing transcranial magnetic stimulation systems

We explain the process of designing optimized transcranial magnetic stimulation systems and outline a method for identifying optimal system parameters such as the number of turns, the capacitor size, the working voltage, and the size of the stimulation coil. The method combines field analysis, linear and nonlinear circuit analysis, and neural strength-duration response parameters. The method uses boundary-element analysis to predict the electric field as a function of depth, frequency, current, and excitation coil size. It then uses the field analysis to determine the inductance as a function of size and, in general, current when a saturable core is used. Circuit analysis allows these electric field computations to be indexed against system parameters, and optimized for total system energy and stimulation coil size. System optimizations depend on desired stimulation depth. A distinguishing feature of the method is that it inherently treats excitation frequency as an unknown to be determined from optimization.     

磁流变阻尼器简化力学模型研究

基于磁流变液体在不同磁场和剪切率下流变特性和磁流变阻尼器在混合模式下的力学原理,推导出包含四个待定系数的磁流变阻尼器简化力学模型。利用MTS8701系统测试的磁流变阻尼器的阻尼力与活塞杆运动速度及励磁电流的试验数据,对磁流变阻尼器简化力学模型进行了系数辩识。用磁流变阻尼器的电压驱动和电磁系统动态响应时间加上磁流变液体成链时间作为磁流变阻尼器的响应时间,建立了带时滞因子的磁流变阻尼器简化力学模型。试验与仿真分析结果表明,该简化力学模型能反映其基本力学特性。     

Vibration Analysis of Tb-Dy-Fe Magnetostriction Actuator and Transducer

In this paper, theoretical analysis of longitudinal free vibration was carried out for Tb-Dy-Fe series magnetostrictive actuator and transducer. The formulations considered two constitutive laws; in one we employ the standard square nonlinear constitutive equation of magnetostriction and in the other we employ the linear piezomagnetic equation. The results obtained from the nonlinear equation can be reduced to the linear piezomagnetic equation when the amplitude of the excitation magnetic field provided by the coil is very small compared to the bias magnetic field and its frequency does not induce resonance of the system. For the case of a relatively large excitation magnetic field, which usually exists for an actuator, the nonlinear constitutive equation should be adopted in order to provide an accurate prediction for the design and analysis of actuator and transducer. Another important aspect is the resonance of the Tb-Dy-Fe series transducers that was revealed in the analysis using the nonlinear constitutive equation. The resonance not only appears at the natural frequencies of the system, but also arises when the frequency of excitation current in the coil happens to be half of one of the natural frequencies of the system. This conclusion cannot be reached using the linear piezomagnetic formulation.     

叠层型磁流变弹性体智能隔震支座及其磁场有限元分析

磁流变弹性体（magnetorheological elastomers,简称MRE）是由天然橡胶或者硅橡胶基体和磁性颗粒组成的新型智能材料,其剪切性能和储能模量可以随着外加磁场的改变而变化。本文创新地提出利用磁流变弹性体材料代替普通橡胶材料,利用其磁流变效应设计制作叠层型智能隔震支座的思路,并且对自行设计的智能隔震支座进行了磁场有限元分析。建立了单线圈磁能输入和双线圈磁能输入结构的二维有限元模型,分别改变支座上下连接板厚度、线圈匝数、电流的大小,分析磁流变弹性体处磁感应强度的变化情况,从而得到电流大小以及支座的结构尺寸与磁感应强度之间的关系。分析结果表明：智能隔震支座磁流变弹性体处的磁感应强度最大可以达到1.2T,该调节范围可以充分发挥磁流变弹性体的流变效应,说明本文提出的新思路是完全可行的。     

Coil geometry models for power loss analysis and hybrid inductive link for wireless power transfer applications

This paper presents a hybrid inductive link for Wireless Power Transfer (WPT) applications. Achieving better power transfer efficiency over a relatively wider distance across coils is the prime objective in most of the WPT systems, but often suffers from power loss in the near field area of inductively coupled coils. One of the reasons for this power loss is the pattern of the magnetic field produced by the source coil used in the WPT system. Mostly the nature of magnetic field produced by the source coil is distributed radially over the coil, in which the produced magnetic field is not fully utilized. Achieving better efficiency and load current by reducing power loss is the main driving force of this work. One of the viable methods to reduce the power loss is by increasing the field intensity thereby redirecting the flux lines flow to be directional. With this aim, three coils such as solenoid, spiral and conical are designed and simulated to determine the magnetic field strength using Finite Element Method. The conical coil produces the highest self-inductance of 8.63 µH and a field strength of 1.542 Wb with the coil thickness of 3.20 mm. Then, WPT system is demonstrated with the inclusion of Maximum Power Point Tracking algorithm for improving efficiency. The schematic of flux generation of both in the transmitter and receiver sections are demonstrated and analyzed graphically. The efficiency of both simulation and experimental measurements are matched well with similar progression. The effect of parameters (angle, distance, and load resistance) on the efficiency is explored. The outcomes conclude that the inductive coupling has achieved 73% (average case) power transfer wirelessly over a distance of 5 cm with an input voltage of 5 V and 5 MHz frequency.