Numerical and experimental investigations of actuating characteristics of laminated polyvinylidene fluoride actuator used on paraboloidal shells

The effect of a laminated polyvinylidene fluoride (PVDF) actuator is analyzed when partially covering a paraboloidal shell. Models of control forces are established using the thin flexible shell theory and the membrane approximation. Analytical expressions of actuating forces and moments are derived and a parametric study is conducted to evaluate the effects of the physical properties of the actuator on the control forces. To verify the model, experiments were carried out on actuation and open-loop vibration control of a paraboloidal antenna with a much smaller actuator. The experimental results agree well with those obtained analytically. The results indicate the following: The laminated PVDF actuator (LPA) can provide effective control forces with low voltages. The control forces consist of actuating forces and moments, but the effect of the normal actuation force distribution is much greater than that of the actuation moments in controlling the normal vibration. The larger the curvature radius of the paraboliodal shell, the smaller the magnitudes of the required actuating forces. The magnitudes of actuating forces are approximately linear with the number of PVDF layers.     

用于电流传感的声表面波磁致伸缩效应

利用声表面波(SAW)磁致伸缩效应可以实现一种快速、高灵敏度的电流检测方法,但磁致伸缩薄膜内部矫顽力导致了明显的磁滞误差。磁致伸缩薄膜的栅阵化设计可以减小磁致伸缩时薄膜内部矫顽力,抑制磁滞现象,从而实现高灵敏和低迟滞误差的SAW电流检测。结合有限元和耦合模理论对沉积铁钴(FeCo)薄膜栅阵的声表面波电流传感器中的磁致伸缩效应进行分析,对传感响应进行仿真,确定优化的传感结构参数。为验证理论分析,实验研制了频率为150 MHz的声表面波电流传感器件,并结合差分振荡电路及亥姆霍兹线圈,建立传感器测试系统.实验结果表明,磁致伸缩薄膜的栅阵设计大幅降低了迟滞误差,并显著提升了传感器灵敏度。      

新型声表面波电流传感器*

将声表面波技术的快速响应特点与磁致伸缩薄膜的高磁敏特点相结合,可实现一种快速、高灵敏、稳定可靠的新型电流检测技术。传感器由双通道差分式振荡器与沉积在传感通道器件表面的声传播路径上的磁致伸缩薄膜组成。该文基于分层介质中声传播理论及磁致伸缩效应,对声表面波电流传感机理进行了分析,以实现对传感器结构的优化设计。实验研制了采用铁钴(FeCo)薄膜的声表面波电流传感器,测试结果表明,该传感器具有快速响应和高灵敏特点。为抑制磁致伸缩薄膜自身的剩磁效应所带来的高磁滞误差,采用的有效途径是将沉积的磁致伸缩薄膜进行图形化设计。实验结果表明,采用栅阵化FeCo薄膜结构的传感器表现出更高检测灵敏度、更好线性及更低的磁滞误差。     

Thin film magnetoelectric composites near spin reorientation transition

We report the use of a magnetic instability of the spin reorientation transition type to enhance the magnetoelectric sensitivity in magnetostrictive-piezoelectric structures. We present the theoretical study of a clamped beam resonant actuator composed of a piezoelectric element on a passive substrate actuated by a magnetostrictive nanostructured layer. The experiments were made on a polished 150 μm thick 18×3 mm² lead zirconate titanate (PZT) plate glued to a 50 μm thick silicon plate and coated with a giant magnetostrictive nanostructured Nx(TbCo_{2 5nm}/FeCo_5nm) layer. A second set of experiments was done with magnetostrictive layer deposited on PZT plate. Finally, a film/film structure using magnetostrictive and aluminium nitride films on silicon substrate was realized, and showed ME amplitudes reaching 30 V Oe⁻¹ cm⁻¹. Results agree with analytical theory.     

磁致伸缩材料磁弹性内耗的场依赖特性及其用于磁场传感研究

分析和测试了磁致伸缩材料磁弹性内耗的偏置磁场依赖特性,发现Terfenol-D的品质因数(与内耗的量值成反比)强依赖于偏置磁场.利用磁致伸缩材料磁弹性内耗强依赖于偏置磁场的特性,提出了一种静态和准静态磁场的磁传感器方法,即将磁致伸缩材料与压电变压器单元层叠构建一种复合变压器.分析表明:在谐振状态下,复合变压器的输出电压正比于其品质因数,于是复合变压器的输出电压强依赖于偏置磁场;磁致伸缩材料的ΔE效应对复合变压器输出电压的影响很小.制备Terfenol-D/PZT8复合变压器进行了实验,结果表明,在近谐振状态下,当激励输入电压振幅为0.5V时,复合变压器工作的输出电压对静态磁场的灵敏度达到～5.12mV.Oe-1.     

种电热驱动法布里 珀罗光调制器

提出了一种用于显示基于微机电系统的电热驱动法布里 珀罗光调制器.利用多光束干涉理论分析了该调制器的原理及光学特性.分析表明:当腔长为(2k+1)λ/4时,反射光强取极大值|当腔长为2kλ/4时,反射光强取极小值|通过改变腔长可以实现显示.光源谱宽越窄,衬比度越高|干涉级次越低,衬比度越高|衬比度随反射率的增加而减小.借助Ansys软件仿真分析了调制器的驱动特性.加工了器件并搭建实验装置进行了动态响应特性测试实验.结果表明,该调制器具有驱动电压低至3.2 V,响应速度约为5 kHz的良好驱动特性.实验结果初步验证了该结构的可行性.     

The efficiency of a magnetostrictive transducer unit: Part 2

In this second part of our paper, the analytical method of impedance bridge determination of transducer efficiency discussed in Part 1 is applied to experimental observations made on two magnetostrictive transducer units. A resonance impedance bridge circuit suitable for experimental observations on magnetostrictive transducers when an excitation current is superposed on a relatively high polarising dc current is also discussed.     

Design and dynamic evaluation for a linear ultrasonic stage using the thin-disc structure actuator

The design of a novel, single-axis ultrasonic actuating stage has been proposed. It consists of a movable plate, an edge-driving ultrasonic actuator as an actuating device, and a magnetic Magi encoder as a position sensor. The stage is impelled using a friction-contact mechanism by the ultrasonic actuator with long distance movement. Very high actuating and braking abilities are obtained. The stable and precise positioning control of the stage was achieved by using a neural-fuzzy controller. This simple and inexpensive structure of the single-axis stage demonstrates that the mechanical design of ultrasonic actuating concept could be done flexibly according to the requirements for various applications.     

Giant magnetoimpedance in composite wires with insulator layer between non-magnetic core and soft magnetic shell

A method for calculation of the magnetoimpedance in composite wires having an insulator layer between non-magnetic core and soft magnetic shell is described. It is assumed that the magnetic shell has a helical anisotropy and the driving current flows through the core only. The distribution of eddy currents and expressions for the impedance are found by means of a solution of Maxwell equations taking into account the magnetization dynamics within the shell governed by the Landau–Lifshitz equation. The effect of the insulator layer on the magnetoimpedance is analyzed.     

Effect of actuating frequency on plasma assisted detonation initiation

Aiming at studying the influence of actuating frequency on plasma assisted detonation initiation by alternating current dielectric barrier discharge, a loosely coupled method is used to simulate the detonation initiation process of a hydrogenoxygen mixture in a detonation tube at different actuating frequencies. Both the discharge products and the detonation forming process which is assisted by the plasma are analyzed. It is found that the patterns of the temporal and spatial distributions of discharge products in one cycle are not changed by the actuating frequency. However, the concentration of every species decreases as the actuating frequency rises, and atom O is the most sensitive to this variation, which is related to the decrease of discharge power. With respect to the reaction flow of the detonation tube, the deflagration-todetonation transition(DDT) time and distance both increase as the actuating frequency rises, but the degree of effect on DDT development during flow field evolution is erratic. Generally, the actuating frequency affects none of the amplitude value of the pressure, temperature, species concentration of the flow field, and the combustion degree within the reaction zone.     

光纤布拉格光栅电流传感的理论和实验研究

对皮磁致伸缩棒调谐光纤布拉格光栅为基础的新型电流传感器进行了理论和实验研究。将一个光纤布拉格光栅牢固地粘贴在一置于多层螺线管中心部分的磁致伸缩棒上，构成传感头。当通过螺线管的电流改变时，磁致伸缩材料在均匀磁场的作用下产生沿纵向的应变并传递到光纤光栅上，从而导致光纤光栅的布拉格波长移动。外加电流和波长移动之间的关系是线性的，线性调谐的波长范围为0.9nm，电流强度范围为900mA，灵敏度约为1000mA/nm，电流强度可精确到10mA。理论和实验符合得很好。     

Effect of thermal deformation on giant magnetoresistance of flexible spin valves grown on polyvinylidene fluoride membranes

We fabricated flexible spin valves on polyvinylidene fluoride(PVDF) membranes and investigated the influence of thermal deformation of substrates on the giant magnetoresistance(GMR) behaviors. The large magnetostrictive Fe_(81)Ga_(19)(Fe Ga) alloy and the low magnetostrictive Fe_(19)Ni_(81)(Fe Ni) alloy were selected as the free and pinned ferromagnetic layers.In addition, the exchange bias(EB) of the pinned layer was set along the different thermal deformation axes α_(31) or α_(32) of PVDF. The GMR ratio of the reference spin valves grown on Si intrinsically increases with lowering temperature due to an enhancement of spontaneous magnetization. For flexible spin valves, when decreasing temperature, the anisotropic thermal deformation of PVDF produces a uniaxial anisotropy along the α_(32) direction, which changes the distribution of magnetic domains. As a result, the GMR ratio at low temperature for spin valves with EB α_(32)becomes close to that on Si, but for spin valves with EB α_(31)is far away from that on Si. This thermal effect on GMR behaviors is more significant when using magnetostrictive Fe Ga as the free layer.     

Novel trends in the study of magnetically soft Co-based amorphous glass-coated wires

An overview of the recent progress and state-of-the-art results in the investigation of the amorphous glass-coated wires with nearly zero magnetostriction is presented. These versatile microwires display enhanced soft magnetic properties, which make them suitable as sensing elements in various sensors for biomedical and automotive applications. Current results on their magnetic characteristics refer to a major refinement of their core-shell magnetic structure by taking into account the interdomain wall and to the thorough analysis of the magnetization within the outer shell. Experimental techniques such as giant magneto-impedance, magneto-resistance, and magneto-optical Kerr effect measurements are employed to prove the outcome of the theoretical calculations. The impact of the magnetic structure of the outer shell on the propagation of domain walls in bistable amorphous wires is analyzed. Very recent results on the magnetization process in nearly zero magnetostrictive amorphous glass-coated wires with submicron dimensions are also reviewed.     

磁致伸缩超声换能器阻抗匹配网络的设计

根据磁致伸缩超声换能器的等效电路模型和阻抗匹配理论,该文设计了一种优化的π型匹配网络.该网络具有调谐、变阻和滤波的功能,适用于工作在中低频超声频率范围内的磁致伸缩超声换能器系统的阻抗匹配.仿真和实验结果表明:接入该π型阻抗匹配网络后,驱动电源与换能器之间实现了最大功率传输,换能器两端电信号的波形质量得到优化,换能器激励...     

Magnetization and magnetostriction studies of TbFeCo/YFeCo multilayers

Exchange-spring TbFeCo/YFeCo multilayers exhibit interesting magnetic and magnetostrictive properties that are rather promising for application in microsystems. In this paper, we present a study of the effect of the exchange coupling on the magnetic properties of these magnetostrictive multilayers. An exchange bias phenomenon, revealed by a shift of the minor hysteresis loop along the applied field axis, is found as the result of the creation of interfacial domain walls. This effect strongly depends on the magnetic properties of the soft YFeCo layer, and becomes more pronounced at low temperatures due to the enhancement of the magnitude of the exchange coupling between the layers.     

Electric field-induced magnetoresistance in spin-valve/piezoelectric multiferroic laminates for low-power spintronics

Electric field-induced magnetic anisotropy has been realized in the spin-valve-based {Ni₈₀Fe₂₀/Cu/Fe₅₀Co₅₀/IrMn}/piezoelectric multiferroic laminates. In this system, electric-field control of magnetization is accomplished by strain mediated magnetoelectric coupling. Practically, the magnetization in the magnetostrictive FeCo layer of the spin-valve structure rotates under an effective compressive stress caused by the inverse piezoelectric effect in external electrical fields. This phenomenon is evidenced by the magnetization and magnetoresistance changes under the electrical field applied across the piezoelectric layer. The result shows great potential for advanced low-power spintronic devices.     

基于流-热耦合模型的GMM智能构件温升控制系统设计

热效应对超磁致伸缩执行器中超磁致伸缩材料性能产生非常大的影响,从而影响超磁致伸缩执行器的定位精度;提出一种简化的强制水冷策略保证磁致伸缩材料温度恒定;同时建立了超磁致伸缩材料智能构件流-热多场耦合的有限元模型,运用COMSOLMultiphysics 3.4软件对模型进行仿真,仿真结果验证了模型的正确,进一步的实验结果证实了提出的温度控制策略的有效性。     

Numerical simulation of nonlinear magnetic-mechanical-electric coupling effect in laminated magnetoelectric composites

Considering the significant nonlinear magnetoelectric (ME) characteristics in laminated ME composites, we build a numerical model of magnetic-mechanical-electric coupling effect based on the nonlinear magnetostrictive constitutive relation. The change of the ME field coefficients with bias magnetic field predicted by this model shows good agreement with the experimental result, both qualitatively and quantitatively. Furthermore, this paper considers and predicts the magnetoelectric conversion charateristics of laminated ME composites, calculates and analyzes the influence of the thickness ratio of magnetostrictive layer, the geometrical size of laminated composites, the saturation magnetization, and the types of piezoelectric materials on the ME conversion coefficient of ME laminated composites. We believe that this research provides a theoretical basis for the production of magnetoelectric devices with good magnetoelectric conversion characteristics.     

The modeling of the radiation and response green's function of a fluid-loaded cylindrical shell with an external compliant layer

Scattering and radiation of acoustic waves from a fluid-loaded cylindrical shell with an external compliant layer are of interest. The compliant layer can be modeled by a normally reacting impedance layer, which has the advantage that complex compliant layer geometries, such as partial compliant layers, can be considered. A question may, however, arise as to the accuracy of this approach. A more rigorous approach is to model the elastic shell and compliant layer using a multilayer shell theory, which has the disadvantage that it cannot be extended to consider partial layers. In this paper scattering results from the normally reacting compliant layer model are compared to those from the multilayer shell model to show that the two approaches produce similar results, except for thickness resonances of the compliant layer. Having established the consistency between the two approaches, results for the far-field acoustic radiation as a function of frequency and radiation angle for a fluid-loaded shell with an external compliant layer excited by an internal ring force are obtained using the normally reacting impedance layer model. These results clearly show the reduction in the far field radiation due to the presence of the compliant layer.     

Magnetostriction of FM/TbFe (FM=Fe, Py-permalloy, FeCo) coupled bilayer

Choosing TbFe as the magnetostrictive layer and using soft ferromagnetic materials (FM=Fe, Py-permalloy, FeCo) as the inductive layer, we report the magnetization and magnetostriction of the S/FM(10 nm)/TbFe(10 nm) coupled bilayer (S-glass substrate). The magnetization of the coupled bilayer is attributed to the soft ferromagnetic layer and there is no contribution from the TbFe layer. Interfacial exchange interaction plays an important role in determining the magnetostriction of the coupled bilayer. The effect coming from the deposition Argon pressure on the magnetostriction of the coupled bilayer was also investigated.