磁塞式油液磨粒在线收集器的结构设计及数值模拟

油液中的磁性颗粒不仅受到传感器探头中永磁体的吸附力,而且还会受到流动油液对其产生的作用力,对油液流场和磁场中的颗粒进行了受力分析,采用有限元数值计算软件ANSYS和Ansoft Maxwell分别对流场和磁场进行了数值仿真,得到了流场中颗粒受力分布及永磁体结构参数对吸附力的影响规律,反映了空心永磁环空间磁场的变化规律,为以后优化设计提供了理论依据。     

外加磁场下磁性液丝的稳定性分析

对处于外加轴向磁场的影响下的磁性液丝进行数学模拟,研究其稳定性。考虑了磁场的作用,对液丝的长波理论模型进行必要的修正。研究了不同条件下磁性液丝的变化发展过程和受力情况,揭示了外加磁场的作用。结果表明：外加磁场减缓了磁性液丝的破裂过程,磁场力类似于非牛顿流体中的弹性行为,在一定程度上抵消了毛细管力。随着初始磁场强度和磁化率的增大,磁场力逐渐增大。当磁场力显著增大时,液丝的变化发展过程被完全阻碍。     

磁致伸缩纵向导波传感器中偏置磁场的优化设计

偏置磁场大小是磁致伸缩纵向导波传感器设计的关键参数之一,最佳偏置磁场的选择受到材料和激励条件的影响,故要求导波检测系统中偏置磁场可调节性好.目前使用的偏置磁场有两种,其中螺线管线圈产生的磁场信号干扰大,信噪比低,永磁体提供的磁场可调节性不佳.为此,提出一种偏置磁场可以调节的结构方案,并通过该方案研制了一种可以调节的偏置...     

一种软磁薄膜磁滞回线测量系统设计*

影响磁通门传感器性能的关键因素之一是软磁薄膜铁芯的性能,针对传统方法和现有仪器测量软磁薄膜磁滞回线的缺点,在分析了长条形软磁薄膜的退磁问题基础上,给出了退磁场对磁滞回线影响的修正方法。采用STM32单片机、LabView软件及数字积分技术设计了一种低成本、小误差软磁薄膜自动化测量系统。通过对电镀软磁薄膜和软磁合金带材样品的测试,并与振动样品磁强计测试结果相比较,结果表明两者矫顽力的相对误差在10%以内,证明了该系统的有效性和准确性。     

高温超导悬浮系统动力学仿真

研究永磁体-高温超导悬浮系统的动力学特性,针对改善系统的稳定特性,建立了考虑空气阻尼、外磁场干扰的永磁体-高温超导悬浮系统的动力学模型,采用修正的磁通冻结—镜象模型计算永磁体所受的动态悬浮力,计算出初始冷却条件的影响,避免了洛仑兹力积分求和问题,并进行仿真计算,得到了稳定的动态特征.采用Gear法进行两种工况数值计算的...     

导管操作系统中力觉传感器信息的获取与控制研究

针对导管操作系统中力觉传感器反馈力的获取与控制进行了研究,导管前端采用光纤力传感器测量导管的顶端力;导管侧壁采用基于PVDF材料开发的微力传感器来测量导管的侧壁力。该导管操作系统对力觉传感器的输出信息进行了监测,实现了一种带有受力信息监测的主—从模式的新型导管操作系统。实验结果表明:该系统能够较好地实现受力信息的反馈。     

基于电磁传感器的软硬磁防伪材料检测

针对现有金融货币鉴伪识别过程中的磁性检测,仅能检测出磁性信号的有无,无法实现磁性防伪材料软硬磁性质的检测。提出了一种电磁传感器,对新版100元纸币的磁性防伪材料进行了检测。通过Maxwell电磁仿真研究了电磁传感器的磁场分布特性。由于软硬磁防伪材料的矫顽力不同,使得其输出的漏磁特征信号有明显的区别,其中软磁区域为高频的包络曲线。根据输出信号的特征不同,可以鉴别出磁性防伪材料的软硬磁性质,进而可以进一步提高鉴伪识别的精度和可靠性。     

悬臂梁式微型阀的启动和过流特性􀀁

本文分析了各种力的尺寸效应及表面张力对悬臂梁式微型阀启动的影响,得到了阀的开启压力．分析了微型阀的静态和动态过流特性,分别得到了阀的静态压差－流量曲线;当阀片两侧的压差随时间变化时,阀片的启闭与压差的变化之间存在一定的相位差,有可能引起泄漏甚至反向流动．     

T-形磁通集聚器磁场放大特性及影响因素研究

针对微型磁传感器对弱磁场测量灵敏度低的问题,利用软磁材料对外磁场的集聚放大作用来提高磁测系统的灵敏度。重点针对T-形磁通集聚器的轴向磁场放大特性及影响因素进行了分析,并设计了相应的磁通集聚器并进行试验测试。试验表明所设计的T-形磁通集聚器具有很好的磁场线性放大作用,可用于提高弱磁场的测量精度。磁力线在磁通集聚结构内部流动的过程中发生了磁通泄漏现象;T-形磁通集聚器对外部磁场放大了约21倍;磁通集聚器的相对磁导率及空气间隙与外部磁场的放大倍数都呈非线性的关系,结构的长宽之比与外部磁场的放大倍数呈单调递增关系,结构厚度对其几乎没有影响。该研究结果能够为磁通集聚器结构设计及优化方面提供一定的参考价值。     

永磁悬浮带式输送机悬浮支撑系统稳定性研究

建立了永磁悬浮带式输送机悬浮支撑系统三维模型,对不同磁性输送带形状、永磁体布置形式、永磁体形状、偏载条件下永磁悬浮支撑系统稳定性进行了仿真。结果表明:槽型磁性输送带稳定性优于平型、V型磁性输送带,且承载能力表现最稳定;永磁体采用槽型结构时磁性输送带稳定性和承载能力较好;偏载会加剧磁性输送带的跑偏。为有效解决磁性输送带跑偏问题,设计了一种槽型磁性输送带防跑偏装置,通过在槽型磁性输送带两侧安装辅助辊轮,能进一步提高永磁悬浮带式输送机悬浮支撑系统的稳定性。     

Theoretical analysis of a new, efficient microfluidic magnetic bead separator based on magnetic structures on multiple length scales

We present a theoretical analysis of a new design for microfluidic magnetic bead separation. It combines an external array of mm-sized permanent magnets with magnetization directions alternating between up and down with μm-sized soft magnetic structures integrated in the bottom of the separation channel. The concept is studied analytically for simple representative geometries and by numerical simulation of an experimentally realistic system geometry. The array of permanent magnets provides long-range magnetic forces that attract the beads to the channel bottom, while the soft magnetic elements provide strong local retaining forces that prevent captured beads from being torn loose by the fluid drag. The addition of the soft magnetic elements increases the maximum retaining force by two orders of magnitude. The design is scalable and provides an efficient and simple solution to the capture of large amounts of magnetic beads on a microsystem platform.     

Optimal design of a high-speed slotless permanent magnet synchronous generator with soft magnetic composite stator yoke and rectifier load

This paper presents a specific design methodology of a DC generation system using a high-speed slotless generator with surface-mounted magnets and soft magnetic composite (SMC) stator yoke connected to a rectifier. The method is based on an analytical design model of the machine, an electrical model of the machine-rectifier system and a non-linear optimization procedure. The coupling between both models is achieved by a specific correction mechanism during the iterative process that performs an efficient convergence of the optimization procedure. The machine design model is derived from an analytical computation of the two-dimensional magnetic field distribution created by the magnets, the armature currents and the stator eddy currents that circulate in the SMC material. It has been cross-validated by 2D finite element analysis. The design approach is applied to the specifications of a 1.5 MW, 18,000 rpm slotless permanent magnet generator with a rated DC output voltage of 1500 V.     

Modeling, microfabrication and experiments of a free–free cantilever bistable micro mechanism supported with a diamond configuration

Bistable micro mechanisms are gaining great attention in MEMS applications. This paper presents the mechanical modeling and experimental characterization of a bistable torsion/cantilever micro latching mechanism for performing low power bistable relay applications. The bistable micro mechanism consists of two cantilevers which form symmetrical rocker levers. The free–free cantilever is suspended by a diamond skeleton which in turn is attached to a torsion cantilever. A permanent magnet is placed beside for holding the closed state with a permalloy soft magnetic circuit. The special diamond support is designed to enhance the stiffness of the overhang beams. In order to deduce the spring stiffness of system, a mechanical modeling of the leveraged torsion/cantilever system was performed by Castigliano’s theorem. Meanwhile, the magnetostatic latching force was also deduced by the Maxwell electromagnetism theory. Then the device has been prepared by a laminated copper sacrificial layer process. This process can facilitate the fabrication complexities of traditional magnetic device with coil structures. Finally, mechanical performance was characterized by an atomic force microscopy, combined with finite element simulation using ANSYS^™ package and analysis model as well. Two stable states of the micro mechanism were hold successfully with no power consumption by interferoscope profilometry of WYKO optical profiling system.     

磁悬浮带式输送机电磁结构优化

常规磁悬浮带式输送机采用永磁体和电磁铁组合的电磁结构,在磁悬浮支承力需求较高的工况条件下具有易发热、电流损耗大等问题。为解决该问题,提出了一种基于Halbach阵列的电磁结构。以电磁结构磁感应强度最大为目标函数,以电磁结构尺寸和磁感应强度分布范围为约束条件,建立了电磁结构优化数学模型。针对教与学优化(TLBO)算法用于求解电磁结构优化数学模型时容易陷入局部最优的问题,提出了一种改进的TLBO算法,该算法通过筛选引入新种群及改进教学阶段和互学阶段的学习方式,增强种群的多样性和搜索能力。测试结果表明,改进的TLBO算法的准确性和稳定性均优于标准TLBO算法。采用改进的TLBO算法对磁悬浮带式输送机电磁结构优化数学模型进行求解,得到最优电磁结构参数:Halbach阵列中单个永磁体高7 mm、宽9 mm,永磁体块数为7。实验结果表明,相同尺寸条件下,基于Halbach阵列的电磁结构最大磁感应强度相对基于永磁体的电磁结构提高了47.69%。     

Experimental study on band merging of non-linear multi-band piezoelectric energy harvester into single broadband using magnetic coupling

The operational bandwidth of Vibration Energy Harvesters (VEH) is area of concern due to stochastic, time-varying, random and multi-frequency nature of available environmental vibrating sources. Most of the VEH have narrow bandwidth providing usable power at specific frequencies. Efforts have been made to increase the frequency range by introducing non-linear structures and techniques. In this paper, multi-band output of the non-linear Piezoelectric Energy Harvester (PEH) is transformed into single wider band output using additional non-linear phenomenon. Dual region operation of PEH results into two separate band output. First region is the outcome of beam resonance and Centre of Gravity (CoG) shift whereas second region is due to the non-linear behaviour of cylinders. In this work, these separate bands are merged to form a single wider band. For merging these two bands and enhancing the bandwidth of PEH, additional phenomenon is introduced using two permanent magnets. A varying magnetic field by changing the distance between magnets changes stiffness of the cantilever beam and that leads to a change in the resonant frequency of band-I. Thus, the overall process shifts band-I towards band-II. In this work, the two separate bands are merged to have one wider band providing 53.22% more frequency coverage than our previous work with a bandwidth of 47.5 Hz. This band includes vibrational frequency range of 25.65–73.15 Hz at 1.4 g acceleration. Cylinder material and its effect with magnetic interaction is also studied. The magnetic force between two permanent magnets is measured experimentally. Effect of magnetic force on centre resonant frequency of beam is compared with experimental and simulated results. Effect of magnetic force on bandwidth of the device is studied.

     

Design and experimental study of broadband hybrid energy harvester with frequency-up conversion and nonlinear magnetic force

In this paper, a novel broadband hybrid piezoelectric and electromagnetic energy harvester using in the low frequency vibration environment is proposed, which combines nonlinear magnet force and frequency-up conversion mechanism simultaneously. Performances are studied by theoretical analysis and experimental test. Electromechanical governed equations of harvester are established, and analytical solutions of vibration response, output voltage and power are derived. Then, effects of nonlinear force, spacing between low frequency vibration beam and piezoelectric beam, load resistance and input excitation on harvester performances are investigated by experimental test. It can be concluded that the harvester can be used to work at the low-frequency environment efficiently, and the resonant frequency and harvesting bandwidth can be tuned by the nonlinear force between the magnets and the spacing between beams. Moreover, the larger the nonlinear magnetic force and the smaller the distance between two beams, the lower working frequency and the larger bandwidth. Compared with the corresponding linear apartment, output power and bandwidth of proposed harvester are improved 90% and 125% respectively.

     

Fabrication and integration of microscale permanent magnets for particle separation in microfluidics

Microfluidic magnetophoresis is an effective technique to separate magnetically labeled bioconjugates in lab-on-a-chip applications. However, it is challenging and expensive to fabricate and integrate microscale permanent magnets into microfluidic devices with conventional methods that use thin-film deposition and lithography. Here, we propose and demonstrate a simple and low-cost technique to fabricate microscale permanent magnetic microstructures and integrate them into microfluidic devices. In this method, microstructure channels were fabricated next to a microfluidic channel and were injected with a liquid mixture of neodymium (NdFeB) powders and polydimethylsiloxane (PDMS). After the mixture was cured, the resulted solid NdFeB–PDMS microstructure was permanently magnetized to form microscale magnets. The microscale magnets generate strong magnetic forces capable of separating magnetic particles in microfluidic channels. Systematic experiments and numerical simulations were conducted to study the geometric effects of the microscale magnets. It was found that rectangular microscale magnets generate larger \(({\mathbf {H}}\cdot \nabla ) {\mathbf {H}}\) which is proportional to magnetic force and have a wider range of influence than the semicircle or triangle magnets. For multiple connected rectangular microscale magnet, additional geometric parameters, including separation distance, height and width of the individual elements, further influence the particle separation and were characterized experimentally. With an optimal size combination, complete separation of yeast cells and magnetic microparticles of similar sizes (\(4\;\upmu \hbox {m}\)) was demonstrated with the multi-rectangular magnet microfluidic device.     

Magnetic concentration of particles and cells in ferrofluid flow through a straight microchannel using attracting magnets

Concentrating particles to a detectable level is often necessary in many applications. Although magnetic force has long been used to enrich magnetic (or magnetically tagged) particles in suspensions, magnetic concentration of diamagnetic particles is relatively new and little reported. We demonstrate in this work a simple magnetic technique to concentrate polystyrene particles and live yeast cells in ferrofluid flow through a straight rectangular microchannel using negative magnetophoresis. The magnetic field gradient is created by two attracting permanent magnets that are placed on the top and bottom of the planar microfluidic device and held in position by their natural attractive force. The magnet–magnet distance is mainly controlled by the thickness of the device substrate and can be made small, allowing for the use of a dilute ferrofluid in the developed magnetic concentration technique. This advantage not only enables a magnetic/fluorescent label-free handling of diamagnetic particles, but also renders such handling biocompatible.     

一种新型MEMS微驱动器的设计与仿真分析

提出并设计了具有双稳态功能的新型电磁型MEMS微驱动器结构形式。微驱动器由导磁的两端固支的扭梁、两端可自由摆动的悬臂梁,以及永磁体、下磁路和平面线圈组成。永磁体的使用,实现了器件的双稳态功能,从而可以得到低功耗的磁驱动器。通电线圈用来实现器件的姿态转换。对设计的器件进行了电磁仿真分析,验证了器件的双稳态机制,分析表明:铁芯的存在对器件功能有决定性的影响。     

Magnetic active-valve micropump actuated by a rotating magnetic assembly

We report on a high-efficiency and self-priming active-valve micropump consisting of a microfluidic chamber structure in glass that is assembled with a polydimethylsiloxane (PDMS) elastic sheet. The latter comprises two valving membranes and a central pumping chamber actuation membrane, having each an integrated permanent magnet that is magnetically actuated by arc-shaped NdFeB permanent magnets mounted on the rotation axis of a DC minimotor. The choice of this actuation principle allows very low-voltage (0.7 V) and low power (a few 10 mW) operation of the micropump. For the realisation, we use affordable powder blasting glass micropatterning and PDMS molding technologies. A flow rate of 2.4 mL/min and up to 70 mbar backpressure are obtained at the micropump resonance frequency of around 12 Hz, values that are much higher than reported so far for such type of micropump.