A bidirectional magnetic microactuator using electroplatedpermanent magnet arrays

A novel bidirectional magnetic microactuator using electroplated permanent magnet arrays has been designed, fabricated and characterized. To realize a bidirectional microactuator, CoNiMnP-based permanent magnet arrays have been fabricated first on a silicon cantilever beam using a new electroplating technique. In the fabricated permanent magnets, the vertical coercivity and retentivity have been achieved up to 87.6 kA/m (1100 Oe) and 190 mT (1900 G), respectively by applying magnetic field during electroplating. A prototype bidirectional magnetic microactuator has been realized by integrating an electromagnet with a silicon cantilever beam, which has permanent magnet arrays on its tip. By applying a do current of 100 mA and altering its polarity, bidirectional motion on the tip of the cantilever beam has been successfully achieved in the deflection range of ±80 μm     

Resin-bonded NdFeB micromagnets for integration into electromagnetic vibration energy harvesters

A micromachining technique is presented for the fabrication of resin-bonded permanent magnets in the microscale. Magnetic paste is prepared from NdFeB powder and an epoxy resin, filled into lithographically defined photoresist molds or metal molds, and formed into resin-bonded magnets after curing at room temperature. A coercivity of 772.4 kA/m, a remanence of 0.27 T, and a maximum energy product of 22.6 kJ/m³ have been achieved in an NdFeB disk micromagnet with dimensions of Φ200 μm×70 μm. Based on the developed micro-patterning of resin-bonded magnets, a fully integrated electromagnetic vibration energy harvester has been designed and fabricated. The dimensions of the energy harvester are only 4.5 mm×4.5 mm×1.0 mm, and those of the micromagnet are 1.5 mm×1.5 mm×0.2 mm. This microfabrication technique can be used for producing permanent magnets tens or hundreds of micrometers in size for use in various magnetic devices.     

Magnetic composite electroplating for depositing micromagnets

This paper reports a novel magnetic composite materials deposition technique called magnetic composite electroplating (MCE). Thin films and micromagnets arrays of a composite matrix consisting of magnetic particles and a ferromagnetic alloy have been fabricated based on this technique. In a typical MCE process, magnetic particles are electrochemically and mechanically embedded into electroplated ferromagnetic thin films to form a magnetic particle-alloy composite. The magnetic particle selected is a barium ferrite magnet (BaFe/sub 12/O/sub 19/) and the ferromagnetic matrix is a pulse-reverse electroplated CoNiP alloy. The particle embedded fraction (w.t. %) directly affects magnetic properties and is experimentally determined by its energy dispersive spectrum (EDS). Various factors including electrolyte particle concentration, applied current, electrolyte pH, and the presence of cationic surfactants affecting the particle embedded fraction are experimentally investigated. Arrays of BaFe/sub 12/O/sub 19/-CoNiP magnets with a variety of dimensions and features as small as 8/spl mu/m have been realized by MCE. Experimental analysis shows that the composite exhibits magnetic properties, such as a high coercivity (H/sub c/) of up to 1.75/spl times/10/sup 5/ A/m, particularly well suited for MEMS actuators.     

Electromagnetically force balanced polymer accelerometer

An acceleration sensor from polymer has been developed which balances a proof mass by magnetic forces. The sensor is fabricated from a polyimide membrane with conductor paths from gold patterned by photolithography and etching, a frame manufactured by ultrasonic hot embossing, and permanent magnets fixed to the frame. Except the conductor path and permanent magnets, all components are made of polymers on a planar substrate, and then the frame is kinked forming the desired three-dimensional structure. In a first try, a sensitivity of 0.46 V/(m/s²) was achieved, and cross axis sensitivity error was less than 3 %.     

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.     

Permanent magnet micromotors on silicon substrates

Different types of sliding, rolling, or rotating micromotors with rare-earth-based permanent magnet rotors are presented. The magnets move synchronously with rotating or traveling magnetic fields generated by 25-μm-thick gold current lines on silicon substrates. The magnets are guided in channels or openings in the silicon itself or in additional glass layers. For magnets with a typical dimension of 1 mm, forces and torques of 150 μN and 100 nNm could be achieved. Maximum velocities of 24 cm/s and a rotation frequency of 2000 r.p.m. have been measured. Magnetic clamping to the bottom confines the rotor to the system and allows a motor operation at any tilt angle. Noncontact magnetic transmission of forces to drive a ferromagnetic fluid has been demonstrated     

Electromagnetic Two-Dimensional Scanner Using Radial Magnetic Field

In this paper, we present the design, fabrication, and measurement results of a two-dimensional electromagnetic scanning micromirror actuated by radial magnetic field. The scanner is realized by combining a gimbaled single-crystal-silicon micromirror with a single turn electroplated metal coil, with a concentric permanent magnet assembly composed of two concentric permanent magnets and an iron yoke. The proposed scanner utilizes the radial magnetic field rather than using a lateral magnetic field oriented 45deg to the horizontal and vertical scan axes to achieve a biaxial magnetic actuation. The single turn coil fabricated with electroplated copper achieves a nominal resistance of 1.2 Omega. A two-dimensional scanner with mirror size of 1.5 mm in diameter was fabricated. Maximum optical scan angle of 8.8deg in horizontal direction and 8.3deg in vertical direction were achieved. Forced actuation of the gimbal at 60 Hz and resonant actuation of the micromirror at 19.1-19.7 kHz provide slow vertical scan and fast horizontal scan, respectively. The proposed scanner can be used in raster scanning laser display systems and other scanner applications.     

用于微型阀的磁性双稳态系统作用力研究

为了降低微型阀功耗,提出了一种新型磁性双稳态系统。该系统由两块钕铁硼材料环形永磁体和一片软磁片组成,其中软磁片选用钢和坡莫合金作为考查材料。采用有限元仿真的方法对软磁片受到的磁场力进行分析,结果显示:当软磁片半径较永磁体半径偏大10%左右时能够获得磁场力极值,同时通过调整两块永磁体之间的距离,软磁片所受到的磁场力能够比单永磁体作用下的受力大30%以上。对软磁片受力进行了测试并与有限元分析结果进行了比较,吻合较好,实验表明:该磁性双稳态系统能够很好地应用在微型阀当中。     

Magnetic and mechanical properties of micromachined strontiumferrite/polyimide composites

In this work, strontium ferrite/polyimide composite thin films are fabricated and characterized for micromachining applications. The application of these materials in microelectronics and micromachining dictates the use of different polymers than those previously used for conventional plastic magnets due to fabrication compatibility constraints. The material investigated here consists of magnetically anisotropic strontium ferrite particles suspended in a benzophenone tetracarboxylic dianhydride-oxydianiline/metaphenylene diamine polyimide matrix. Magnetic mechanical, and processability properties of these composites are investigated for a strontium ferrite loading range of 55%-80% by volume. Intrinsic coercivity H_ci residual magnetic flux density B_r and maximum energy product (BH)_max have been determined. For an 80% by-volume concentration loading of ferrite, H_ci of 318 kA/m B_r, approaching 0.3 T, and (BH)_max of 11900 T·A/m have been achieved. Biaxial Young's modulus and residual stress are determined using a slightly modified in situ load/deflection technique. The biaxial Young's modulus increases with increasing the magnetic powder loading. The materials have been deposited and patterned using two techniques: (1) screen-printing and (2) spin-casting, followed by photolithography. Finally, a simple magnetic microactuator made with those materials has been fabricated and tested, which demonstrates the usefulness of those materials to micromachining     

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.     

Axial-flux permanent magnet machines for micropower generation

This paper reports on the design, fabrication, and testing of an axial-flux permanent magnet electromagnetic generator. The generator comprises a polymer rotor with embedded permanent magnets sandwiched between two silicon stators with electroplated planar coils. Finite element simulations have been carried out using ANSYS to determine the effects on performance of design parameters such as the number of layers in the stator coils, and the rotor-stator gap. The effect of including soft magnetic pole pieces on the stators has also been studied. A prototype device with a diameter of 7.5 mm has been tested, and shown to deliver an output power of 1.1 mW per stator at a rotation speed of 30 000 rpm. The generator has been integrated with a microfabricated axial-flow microturbine to produce a compact power conversion device for power generation and flow sensing applications.     

Bidirectional actuation of ferrofluid using micropatterned planar coils assisted by bias magnetic fields

This paper reports a ferrofluid control method that enables both attraction and repelling of ferrofluid on micropatterned planar coils coupled with permanent magnets. A combinational use of a controlled magnetic field and a bias field is shown to provide lateral forces that attract/repel the ferrofluid to/from the coil depending on the direction of the current passed through the coil. Active mirror devices whose mirrors are switched by ferrofluids are developed as a proof-of-concept of the actuation method toward the application to imaging devices and optical switches. The planar devices lithographically fabricated to have arrays of mirror-coil cells are used to demonstrate activation/deactivation of individual cells enabled by the bidirectional radial motion of the ferrofluid layer with ∼100 μm thickness. The static and dynamic behaviors of the ferrofluid in the devices are characterized through an image processing approach. Multiple mirror cells are selectively and simultaneously operated to show enhanced ferrofluid control uniquely available with the two modes of the actuation as well as to demonstrate pattern generation with the arrays.     

体内微型机器人的全方位旋进驱动特性

提出了一种由外旋转磁场驱动的体内微机器人．它以相邻径向异向磁化瓦状多磁极圆筒形NdFeB永磁体为外驱动器,以机器人内嵌同结构的NdFeB永磁体为内驱动器,外驱动器旋转时产生旋转磁场,通过磁机耦合作用于内嵌驱动器形成机器人驱动力矩,在本体外表面螺纹与流体动压力的作用下,实现机器人在管道内的在线旋进．在建立微机器人游动模型的基础上,以垂直管道为试验环境,研究了机器人的全方位驱动特性,试验结果表明机器人可以实现管道内全方位驱动．     

Linear displacement sensor based on the magneto-optical Faraday effect

We report in this work the theoretical analysis of a linear displacement sensor based on the magneto-optical Faraday effect. The sensor consists of a rod of a magneto-optically active material that can be dislocated along the axis of a magnetic configuration formed by two equal hollow cylindrical permanent magnets, uniformly magnetized, arranged with opposite polarities. The performance of the sensor is discussed in terms of the inner and outer diameters of the two magnets, the sample and magnet lengths, the residual magnetic-field strength of the permanent magnets, the Verdet constant of the magneto-optically active material and the wavelength of the light source employed. We show that it is possible to have a practical sensor system that is almost linear over a distance equivalent to 90% of the total sample length, with a departure from linearity smaller than 1% and capable of detecting displacements as small as 1 μm when a rod of HOYA FR-5 paramagnetic glass is used as the magneto-optically active medium and a He-Ne laser at 543 nm as light source.     

Electromagnetically actuated biaxial scanning micromirror fabricated with silicon on glass wafer

In this paper, we present an electromagnetically actuated two-axis scanning micromirror with large aperture and tilting angle for laser pointing applications. The two-axis micromirror with the plate size of 3 mm in diameter was realized using gimbaled single crystal silicon with a single-turn electroplated copper coil, and it was assembled with permanent magnets forming radial magnetic field. The micromirror was fabricated on SiOG (Silicon on Glass) wafer using 4 photolithography masks. The permanent magnet assembly composed of a cylindrical and a ring-type magnet was designed to optimize the radial magnetic field, and thus maximize the torque on the coil. Three different magnet assemblies were applied to the fabricated micromirror in order to verify the design. Horizontal resonance frequency of the fabricated micromirror was measured 1.421 kHz and vertical resonant frequency was 396 Hz. The vertical scan angle was 16.87°, 26.32° and 22.61° with the cylindrical magnet diameter of 2.6, 4.0 and 4.8 mm, respectively, at 60 Hz sinusoidal input of 640 mA_pp. For horizontal scan, maximum scan angle of 24.45° was obtained at 48 mA_pp input signal in resonance mode. In addition, the temperature distribution on the micromirror surface was measured with the applied current to the coil.

     

Synthesis and performance evaluation of thin film PPy-PVDF multilayer electroactive polymer actuators

Bending-type microactuators less than 1 mm in length and comprising of two polypyrrole (PPy) layers separated by polyvinylidene fluoride (PVDF) membrane have previously been fabricated and was shown to operate both in air and aqueous media. The main limiting factor to increase the bending angle and to further miniaturise these actuators was the thickness of the commercially-available PVDF membrane used (～110 μm). In this study, we have synthesised a porous PVDF thin film with a thickness of 32 μm using a spin coating technique, and electrochemically deposited PPy layers on both sides of this thin film to make ultra thin film polymer actuators. The electromechanical and electrochemical properties are investigated and compared with those of the thicker actuator system using the commercially-available PVDF and under identical conditions. The thin film shows very promising performance compared to its thicker counterpart.     

An electrostatic microactuator system for application in high-speedjets

The development of an electrostatic microactuator system for the study and control of high-speed jet flows is presented. The electrostatic actuator is 1.3 mm wide, 14 μm thick and has a head that overhangs a glass substrate, intruding into the flow by 200 μm. The actuator has been fabricated using a bulk-silicon dissolved-wafer process to increase device thickness for increased stiffness in the flow direction. Characterization of the new actuators demonstrated their ability to oscillate with amplitudes of up to 70 μm peak-to-peak at resonant frequencies of 5 and 14 kHz. This is a very large motion at such high frequencies when compared to existing macro or micro mechanical actuators. The full actuator system was mounted around the exit of a high-speed jet using several sector-shaped PC boards. This enabled detailed examination of the ability of the actuators to withstand the flow environment and generate substantial flow disturbances. The results showed that the microactuators functioned properly up to jet speeds of 300 m/s while generating disturbances in the shear layer surrounding the jet comparable to those produced by other macro-scale methodologies     

Design and analysis of a wall-climbing robot for passive adaptive movement on variable-curvature metal facades

To facilitate the safe adsorption and stable motion of robots on curved metal surfaces, a wall-climbing robot with a wheeled-type mobile mechanism that can passively self-adapt to walls with different curvature is proposed. The robot is composed of two relatively independent passive adaptive mobile mechanisms and overrunning permanent magnetic adsorption devices to achieve effective fitting of the driving wheels to the wall surface and adaptive surface motion. The overall design is based on a double-hinged connection scheme and gap-type permanent magnetic adsorption. The minimum adsorption force required for the robot to achieve stable climbing motion with no risk of slipping or capsizing is determined by developing a static analysis model. The effects of air-gap size and wall thickness on the adsorption force are analyzed by means of magnetic circuit design studies and parametric simulations on the permanent magnet adsorption device, as well as design optimization of the permanent magnet device. The motion performance test of the fabricated prototype shows that the robot can achieve adaptive curvature motion with self-attitude adjustment, and has a certain load capacity, obstacle crossing capability, and good surface adaptivity.     

Controlled counter-flow motion of magnetic bead chains rolling along microchannels

We demonstrate controlled transport of superparamagnetic beads in the opposite direction of a laminar flow. A permanent magnet assembles 200 nm magnetic particles into about 200 μm long bead chains that are aligned in parallel to the magnetic field lines. Due to a magnetic field gradient, the bead chains are attracted towards the wall of a microfluidic channel. A rotation of the permanent magnet results in a rotation of the bead chains in the opposite direction to the magnet. Due to friction on the surface, the bead chains roll along the channel wall, even in counter-flow direction, up to at a maximum counter-flow velocity of 8 mm s⁻¹. Based on this approach, magnetic beads can be accurately manoeuvred within microfluidic channels. This counter-flow motion can be efficiently be used in Lab-on-a-Chip systems, e.g. for implementing washing steps in DNA purification.     

Design of a yield stress characterizing platform for magnetorheological fluid magnetized by permanent magnets

In this paper we proposed a platform for measuring shear force of magnetorheological (MR) fluid by which the relationship of yield stress and magnetic flux density of specific materials can be determined. The device consisted of a rotatable center tube placed in a frame body and the magnetic field was provided by two blocks of permanent magnets placed oppositely outside the frame body. The magnitude and direction of the magnetic flux were manipulated by changing the distance of the two permanent magnets from the frame body and rotating the center tube, respectively. For determining the magnetic field of the device, we adopted an effective method by fitting the finite element method result to the measured one and then rebuilt the absent components to approximate the magnetic field, which was hardly to be measured as different device setup were required. With the proposed platform and analytical methods, the drawing shear force and the corresponding yield stress contributed by MR fluid in respect to the magnitude and direction of given magnetic flux density could be evaluated effectively for specific designing purposes without the requirement of a large, complex, and expensive instrument.