Electromagnetic Microactuator Research Articles

Development of a flexible coil based on conductive polymer composite for PDMS-based soft electromagnetic microactuators

Development of a flexible coil based on conductive polymer composite for PDMS-based soft electromagnetic microactuators

Fast Current Control Based on Indirect Current Sensing of The Full-Bridge Converter Associated with An Electromagnetic Micro-Actuator

This paper deals with the fast current control of the full-bridge converter loaded with a digital electromagnetic micro-actuator. Input current sensing method is proposed for the initial full-wave control of output current. Input current analysis takes parasitic parameters into account and shows that input current approximately equals output current during the full-wave state. The peak value of input current during steady state is twice the output current. A multi-scale closed-loop control is then implemented, which ensures stable fast current control. In the micro-actuator application, converters are tightly integrated with micro-actuator at output side. Input shunt sensor is easier to implement and has lower power dissipation compared with output shunt sensor. This solution has been validated with an experimental test bench. FPGA board is used to implement the proposed control strategy. Experimental results show that the start-up duration is greatly reduced, thereby realizing the fast current response.

Multilayered Microcoils for Microactuators and Characterization of Their Operational Limits in Body-Like Environments

Multilayered microcoils are of great importance for the development of advanced electromagnetic microactuators and especially important to develop high-sensitivity microsensors and magnetic field neural stimulators for medical applications. A clean room-free procedure for manufacturing multilayered micrometric coils is presented in this article. The production of miniaturized multilayered coils from tens to hundreds of micrometres long is demonstrated. The microcoils have outer diameters ranging between 150 and 300 μm, arrangements of up to five consecutive layers, and an average fill factor of 85%. This means three times smaller diameters than the smallest diameter ever achieved by winding techniques while keeping a high fill factor and a large number of layers. Such small and highly performant microcoils have never been demonstrated neither by winding processes nor epitaxial growth techniques. These microcoils were tested inside different human body-like environments. Maximum current density versus temperature was measured in air, fat tissue, muscle tissue, and simulated body fluid at 36 °C. A maximum current density of 3600 A/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> has been measured before coil failure. Experiments demonstrated that current densities of up to 610 A/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> can safely be supplied to coils without risk of harm to internal tissues. These counterintuitive values are orders of magnitude larger than typical current densities used in macroscale actuators windings.

A novel electromagnetic microactuator with a stainless steel mas-spring structure

Microactuators are one of the main components of the microelectromechanical and microfluidic systems and play a key role in their development. Many such systems, e.g. micropumps and microvalves, utilize an electromagnetic microactuator with a displacement range of a few micrometers traversed within a few seconds. Most of the electromagnetic microactuators have low lifetime and fracture toughness or low recovery speed. Microactuators with metallic mass-spring structure can overcome the mentioned disadvantages or limitations. This paper presents the design and fabrication of a novel stainless steel electromagnetic microactuator fabricated using micro-wire electrical discharge machining. The microactuator in question consists of a mass-and-spring structure made of 304 stainless steel, a permanent magnet made of NdFeB, and a microcoil. The impacts of the number of turns, distance, and electric current on the magnetic field of the microcoil and the displacement of the microactuator membrane with time have been investigated to determine the microactuator characteristics. The results indicated a displacement of about ±10 (20) μm within 7 s for an electric current of 1100 mA. This microactuator exhibits a faster response compared to the similar microactuators. Consequently, it can be used at higher operating frequencies and, thus, improves the fluid flow in micropumps.

Moving coil type electromagnetic microactuator using metal/silicon driving springs and parylene connecting beams for pure in-plane large motion in three axes

In this paper, we report a three-degree-of-freedom electromagnetic microactuator with pure in-plane bi-directional displacement in X and Y and rotation about Z. Moving coil scheme was adopted because pure in-plane actuation without vertical displacement was possible under a uniform magnetic field. The actuator mainly consists of four driving units and a center moving stage within a footprint of 6 mm × 6 mm. Each of the driving unit is formed by four driving springs made of silicon and gold and connected by a moving shuttle. Parylene was employed to make spring beams to connect the center moving stage and the shuttles of four driving units. In-plane Lorentz force was generated by the coupling between current in the driving springs and a uniform outer magnetic field. By controlling the strength of current and outer magnetic field, an in-plane bi-directional displacement as large as ± 40 µm in X and Y and rotation angle of ± 2 degrees about Z were measured, the corresponding resonant frequencies were 650 Hz and 780 Hz, respectively.

Design, fabrication, and characterization of an SLA 3D printed nanocomposite electromagnetic microactuator

Electromagnetic microactuators are a key component of the membrane-based microelectromechanical devices to provide controllable and precise movements. However, their fabrication by traditional soft lithography remains a time-consuming, labor-intensive, and high-cost operation. This paper presents a novel material used in this SLA 3D printed electromagnetic nanocomposite microactuator, which has advantages in costs and time saving by a simplified fabrication process and minimum chances of human interactions. The nanocomposite magnetic microactuator consists of Fe3O4 nanoparticles with excellent magnetic properties dispersed in a photo-polymerizable FLGPCL04 resin. First, the coil specifications include the temperature and magnetic field of the coil are examined to control the microactuator performance. After that, the effect of variation in coil turn number, coil current, and Fe3O4 nanoparticle concentration on the microactuator performance is investigated to improve the membrane displacement. The membrane with 5 wt-% nanoparticles concentration has achieved a displacement of 65 μm for an electric current of 1000 mA in 12 s. To control the return time of the membrane and reduce the recovery time, a bidirectional structure is used in the proposed microactuator. With this mechanism, it takes 10 s to return the nanocomposite membrane of the microactuator to the original location after achieved maximum displacement.

Interleaved phase-shift full-bridge DC/DC converters for an electromagnetic micro-actuator

Two low voltage parallel full-bridges are proposed for the power supply of a two-axis electromagnetic micro-actuator. GaN FETs are chosen for these converters to achieve high efficiency while switching at high frequencies. The control strategy implements the phase shift between two branches of each full-bridge and the interleaved phase between two full-bridges, which reduces the load current ripple and increase the frequency of input and output current ripples. These properties help us miniaturize filtering coils and decoupling capacitors associated to the converters. The test bench that highly integrates the micro-actuator and converters was fabricated. Simulation and experimental results are compared for analysing and validating the integration and the proposed control strategy.

The Finite Volume Method an Alternative Method for LF Electromagnetic Problems

Currently, many simulation tools based on numerical methods are available for modelling of low frequency electromagnetic problems such as eddy current related problems, electrical machines and electromagnetic actuators analysis. Commonly, it’s the finite element method (FEM) which is used; nevertheless, the exploit of other numerical approaches, such as the finite volume method (FVM) can be strongly promising. Accordingly, the main purpose of this paper is to present the FVM method as an alternative method for low frequency electromagnetic problems. Thus, 2D and 3D FVM computer codes are developed and examined through the analysis of two TEAM workshop problems and an experimental electromagnetic micro-actuator. These types of problems are habitually analyzed by the FEM method. By using the FVM method, the solution of the above listed problems includes eddy current, torque and magnetic force computation.

An in-plane, large-stroke, multipole electromagnetic microactuator realized by guideways stacking mechanism

In the application of cell phone cameras, it is essential to design optical image stabilizers with tiny size, in-plane motion and large stroke. Previously, small sized voice-coil actuators utilizing assembled magnets have been developed to achieve displacements up to 500 μm. Here, we propose a novel MEMS electromagnetic actuator employing a multipole permanent magnet with a finely pitched chessboard pattern and stacked multilayer Si-based guideways, enabling us to obtain a large stroke at low driving voltages. The magnet, which has multiple poles (pole number: 36) and a fine pitch (magnetization pitch: 1 mm), is realized by a combination of laser assisted heating and an external magnetic field, utilized to enhance the magnetic strength. For the support mechanism, stacked multilayered Si-based guideways are adopted to reduce the friction in the driving x- and y-directions and increase the rigidity in the non-driving z-direction. Driving experiments showed the proposed microactuator was capable of both independent 1-DOF motion and simultaneous 2-DOF motion with driving frequencies varying from 1 to 15 Hz. For the independent 1-DOF motion, an approximately straight line trajectory with a maximum stroke of 760 μm was obtained with an AC of 160 mA at a frequency of 1 Hz. In the simultaneous 2-DOF motion, a quasi-circular trajectory with a maximum stroke of 280 μm was achieved when the coil currents were set as follows: frequency of 1 Hz, current amplitude of 120 mA in the x-direction, current amplitude of 140 mA in the y-direction, phase difference of 90°between the x- and y-directions. This promising structure utilizing a finely pitched multipole permanent magnet and stacked multilayered guideways improves the stroke at a low driving voltage and in the small size.

Electromagnetic Digital Microactuators Remote Control by a Parallel Dual Wavelengths Optical Communication System

In this paper, a parallel dual wavelength optical communication channel is presented. A custom optical sensor based on a double Fabry-Perot structure is described. It allows the system to instantaneously demultiplex the incident wavelengths as well as offers noise rejection, such as ambient light. It allows sending two bits in only one pulse of light. Contrary to other optical approaches, the presented approach differs in that it uses a wide optical spectrum and only inexpensive electronics. The usefulness of this free space, point-to-point, communication channel is demonstrated in the remote control of an electromagnetic digital microactuator. Thanks to a proper algorithm in the receiver, the proposed system is able to control all the degrees of freedom of the microactuator with a movement for every pulse of light.

An electromagnetic micro-actuator with PDMS-Fe3O4 nanocomposite magnetic membrane

Polydimethylsiloxane-Fe3O4 nanocomposite is introduced as a competent magnetic material to utilize in the magnetic membrane micro-actuators, for first time in this paper. Using this magnetic composite, two types of electromagnetic micro-actuators are presented in this paper: unidirectional micro-actuator and bidirectional micro-actuator. In all the other similar micro-actuators already proposed in the literature, a unidirectional actuating mechanism has been used where there is no control on the return time of the membrane and where the return time is very long. To solve this problem, a bidirectional micro-actuator is proposed in the present article, where the return time of the magnetic membrane can be controlled as well as the forward time. Using this micro-actuator, we achieved a favorable membrane deflection of 8 μm in merely 2 s (compared to the deflections of 9.16 and 12.87 μm in 60s, reported by the recent papers) as well as a considerable displacement of 66 μm in 20 s. In our proposed micro-actuator, the stress and strain developed in the magnetic membrane (at identical displacements) are far less than those developed in a unidirectional micro-actuator, an advantage that would increase the life of the magnetic membrane. The effective parameters on the performance of the magnetic nanocomposite micro-actuator including the number of coil turns, electric current, concentration of Fe3O4 nanoparticles, and the spacer thickness were also investigated.

Design and Analysis of Non-spiral Planar Microcoil-Based Electromagnetic Microactuator

Lab-on-chip devices essentially require micropumps and valves which incorporate a microactuating mechanism to control fluid flow. In this work, a non-spiral type planar microcoil is reported for implementing an electromagnetic microactuator. The effect of variation in coil geometries on the microactuator performance is analyzed for the first time. The microcoil fabricated and characterized in this work considerably reduces the number of lithography layers, thus improving the ease of fabrication while reducing the series coil resistance. The microcoil structures are further analyzed for the microactuator performance using finite element method, and the effect of coil geometries on the electromagnetic force generated by the actuator is studied. Microfabrication and electrical characterization results of the non-spiral planar microcoils show the influence of the same on the actuator performance. A tapered square microcoil geometry is proposed to improve the outputs from the actuator.

Design and experimental investigation of a bi-directional valveless electromagnetic micro-pump

In this paper, a design of a novel electromagnetic micro-actuator prototype is presented. This prototype is fabricated using conventional elements for a novel working principle as bi-directional valveless micro-pump for biomedical applications. The proposed micro-pump includes two unfixed permanent magnets placed in opposite polarities in a cylindrical channel. The channel is placed between two fixed coaxial coils as external electromagnets. The electromagnetic actuating depends on moving both unfixed permanent magnets vertically via the interaction of their magnetic fields and that resulting from coils. The actuation of magnets is produced with a periodic movement and consists mainly of three main modes. By selecting a suitable coil’s driving currents, the actuation can be controlled either to change fluid flow direction or the actuation speed. An experimental test shows the high performance of the proposed micro-pump, a flow rate of 37 ml/mn and maximum back pressure of 1.98 kPa are attained.

Electromagnetic Microactuators using Non-spiral Planar Microcoils for Robotic Applications

Electromagnetic microactuators offer several advantages for robotic applications such as relatively large stroke and low input voltage requirements. Micro coils are significant components for electromagnetic microactuators for generating force required for micro robots. Non-spiral planar microcoils of square and circular geometries are analyzed here considering the fabrication easiness and low power consumption of non-spiral planar coils. Microfabrication of non-spiral planar coil is simpler and requires a single mask process only. Comparison between non-spiral coils and conventional spiral coils are also discussed. Series resistance of non-spiral coil is found out to be lesser than that of spiral coils though magnetic field is slightly lesser for non-spiral coils. The fabrication advantages and low power dissipation of non-spiral structures make them a strong alternative for conventional spiral planar microcoils. Comparison of different planar microcoils shows that the circular non-spiral coil gives better performance than other coil geometries considered here for robotic applications. Circular coil is found to provide a uniform field with lesser parasitic resistance. Electromagnetic microactuator using non-spiral planar circular and square microcoils are also analyzed to compare the performance between the two coil types. The results show that the force generated using non-spiral circular microcoil in the microactuator is adequate for microrobotic applications with an added advantage of uniform magnetic field provided by the circular coils.

Feasibility of Round Window Stimulation by a Novel Electromagnetic Microactuator.

Introduction Most implantable hearing aids currently available were developed to compensate the sensorineural hearing loss by driving middle ear structures (e.g., the ossicles). These devices are successfully used in round window (RW) stimulation clinically, although this was initially not the intended use. Here, a novel microactuator, specifically designed for RW stimulation, was tested in human temporal bones to determine actuator performance and applicability. Methods Stapes footplate response to RW stimulation was determined experimentally in human temporal bones and the obtained sound pressure output level was estimated. Results The actuator had a flat displacement response between 0.125 and 4 kHz, a resonance between 4 and 7 kHz, and a roll-off above. At increasing contact force, the stapes footplate displacement decreased by 5–10 dB re μm for forces ≥ 2 mN. The equivalent sound pressure level between 0.125 and 4 kHz amounted to 87–97 eq dB SPL and increased to 117 eq dB SPL for frequencies of 4–7 kHz. The total harmonic distortion (THD) of the actuator ranged within 15–40% for static forces of 5 mN. Conclusion The feasibility of an electromagnetic actuator that may be placed into the RW niche was demonstrated but requires further optimization in terms of THD and static force sensitivity.

Design and Fabrication of Compact MEMS Electromagnetic Micro-Actuator with Planar Micro-Coil Based on PCB

This paper reports a compact design of electromagnetically driven MEMS micro-actuator utilizing planar electromagnetic coil on PCB (Printed Circuit Board). The micro-actuator device consists of an NdFeB permanent magnet, thin silicon membrane and planar micro-coil which fabricated using simple standard MEMS techniques with additional bonding step. Two planar coils designs including planar parallel and spiral coil structure with various coil geometry are chosen for the study. Analysis of the device involves the investigation of electromagnetic and mechanical properties using finite element analysis (FEA), the measurement of the membrane deflection and functionality test. The measurement results show that the thin silicon membrane is able to deform as much as 12.87 µm using planar spiral micro-coil. Reasonable match between simulation and measurement of about 82.5% has been revealed. The dynamic response test on actuator driven by parallel planar coil shows that silicon membrane effectively deformed in 40 s for an input electrical power of only 150 mW. It is also concluded that planar parallel coil is considered for the simple structure and easy fabrication of the actuator system. This study will provide important parameters for the development of compact and simple electromagnetic micro-actuator system for fluidic injection system in lab-on-chip.

A novel two-axis micromechanical scanning transducer using water-immersible electromagnetic actuators for handheld 3D ultrasound imaging

This paper reports the development of a new two-axis micromechanical scanning transducer for handheld 3D ultrasound imaging. It consists of a miniaturized single-element ultrasound transducer driven by a unique 2-axis liquid-immersible electromagnetic microactuator. With a mechanical scanning frequency of 19.532Hz and an ultrasound pulse repetition rate of 5kHz, the scanning transducer was scanned along 60 concentric paths with 256 detection points on each to simulate a physical 2D ultrasound transducer array of 60×256 elements. Using the scanning transducer, 3D pulse-echo ultrasound imaging of two silicon discs immersed in water as the imaging target was successfully conducted. The lateral resolution of the 3D ultrasound image was further improved with the synthetic aperture focusing technique (SAFT). The new two-axis micromechanical scanning transducer does not require complex and expensive multi-channel data acquisition (DAQ) electronics. Therefore, it could provide a new approach to achieve compact and low-cost 3D ultrasound imaging systems, especially for handheld operations.

Microfabricated water-immersible scanning mirror with a small form factor for handheld ultrasound and photoacoustic microscopy

Microscanning mirrors that can operate reliably under water are useful in both ultrasound and photoacoustic microscopic imaging, where fast scanning of focused high-frequency ultrasound beams is desired for pixel-by-pixel data acquisition. We report the development of a new microfabricated water-immersible scanning mirror with a small form factor. It consists of an optically and acoustically reflective mirror plate which is supported by two flexible polymer hinges and driven by an integrated electromagnetic microactuator. It can achieve 1-axis scanning of ±12.1 deg at a resonant frequency of 250 Hz in air and 210 Hz in water, respectively. By optimizing the design and enhancing the fabrication with high-precision optical three-dimensional printing, the overall size of the scanning mirror module is less than 7 mm×5 mm×7 mm. The small form factor, large scanning angle, and high-resonant frequency of the new water-immersible scanning mirror make it suitable for building compact handheld imaging probes for in vivo high-speed and wide-field ultrasound and photoacoustic microscopy.

Electromagnetic Micromotors—Design, Fabrication and Applications

Microactuators have become essential elements of microelectromechanical systems, for example, for positioning purposes and for fluid-handling tasks in microfluidic systems. UV depth lithography and other new micromachining technologies, which have been developed since the 1990s, have initiated extensive investigations of electromagnetic microactuators, which are characterized by high forces, large deflections, low driving voltages resulting from low input impedances and robustness under harsh environments. This paper reviews the comprehensive research on the design, fabrication and application of electromagnetic micromotors performed in our laboratory over the past years.

A compact electromagnetic micro-actuator using the meander springs partially exposed to magnetic field

We present the design, fabrication, and testing of a compact electromagnetic micro-actuator using meander springs that are partially exposed to the magnetic field. The previous electromagnetic micro-actuators using cantilever springs require large electromagnetic force for large displacement actuation and therefore require high-current input and a large magnet. The previous electromagnetic actuators using low-stiffness meander springs are limited in large displacement actuation because actuation forces cancelled each other due to changes in the current path under the magnetic field. In this paper, we compare two prototypes: a conventional prototype F with the meander springs exposed fully to the magnetic field and the present prototype P with the meander springs partially exposed to the magnetic field. In the experimental study, the amplitude of prototype P is measured as 30.49 � 0.36 µm at the 40 mA square input current, while the amplitude of prototype F is measured as 26.02 � 0.65 µm. The amplitude of prototype P is 17.2 % larger than that of prototype F, verifying the effect of partial exposure of the meander springs to the magnetic field. Therefore, we experimentally demonstrate the large-displacement actuation performance of the present actuator using the partial exposure of the meander springs to the magnetic field.