Microactuator Applications Research Articles

Dynamic modelling and experimental study of asymmetric optothermal microactuator

This paper reports the dynamic modelling and experimental study of an asymmetric optothermal microactuator (OTMA). According to the principle of thermal flux, a theoretical model for instantaneous temperature distribution of an expansion arm is established and the expression of expansion increment is derived. Dynamic expansion properties of the arm under laser pulse irradiation are theoretically analyzed indicating that both of the maximum expansion and expansion amplitude decrease with the pulse frequency increasing. Experiments have been further carried out on an OTMA fabricated by using an excimer laser micromachining system. It is shown that the OTMA deflects periodically with the same frequency of laser pulse irradiation. Experimental results also prove that both OTMA’s maximum deflection and deflection amplitude (related to maximum expansion and expansion amplitude of the arm) decrease as frequency increases, matching with the theoretical model quite well. Even though the OTMA's deflection decrease at higher frequency, it is still capable of generating 8.2μm maximum deflection and 4.2μm deflection amplitude under 17Hz/2mW laser pulse irradiation. This work improves the potential applications of optothermal microactuators in micro-opto-electro-mechanical system (MOEMS) and micro/nano-technology fields.

On the thermo-mechanical behavior of NiTi shape memory elements for potential smart micro-actuation applications

Among smart and functional materials, the shape memory alloys are enabling the development of a new class of devices for the automotive, aerospace, biomedical, and mechanical applications based on the shape memory and superelastic effects. In this work, a study on the mechanical response of NiTi shape memory micro-elements, in the so-called “snake-like” configuration, is reported. These elements were patterned by means of laser micro-processing from thin NiTi sheets and then chemically etched. Different micro-elements, as function of the number of the curvatures replicated, were fabricated and tested. The functional performances of the micro-elements were characterized through calorimetric analysis for the definition of the operating temperatures and through thermo-mechanical testing for the evaluation of their actuating response. Mechanical tests were carried out to assess the tensile behavior of martensite and austenite phases separately, and for evaluating the thermal hysteresis under different constant loads during cooling/heating loops. Moreover, finite element modeling was also accomplished to analyze the stress distribution in both the martensitic and austenitic phases as loading.

Devices Based on Co-Integrated MEMS Actuators and Optical Waveguide: A Review.

The convergence of Micro Electro Mechanical Systems (MEMS) and optics was, at the end of the last century, a fertile ground for a new breed of technological and scientific achievements. The weightlessness of light has been identified very early as a key advantage for micro-actuator application, giving rise to optical free-space MEMS devices. In parallel to these developments, the past 20 years saw the emergence of a less pursued approach relying on guided optical wave, where, pushed by the similarities in fabrication process, researchers explored the possibilities offered by merging integrated optics and MEMS technology. The interest of using guided waves is well known (absence of diffraction, tight light confinement, small size, compatibility with fiber optics) but it was less clear how they could be harnessed with MEMS technology. Actually, it is possible to use MEMS actuators for modifying waveguide properties (length, direction, index of refraction) or for coupling light between waveguide, enabling many new devices for optical telecommunication, astronomy or sensing. With the recent expansion to nanophotonics and optomechanics, it seems that this field still holds a lot of promises.

Mechanical and electrical properties of electrospun CNT/PVDF nanofiber for micro-actuator applications

Electrospun polyvinylidene fluoride (PVDF)-containing carbon nanotubes (CNT) were prepared for use in fabricating actuator materials. Actuating displacement was measured in an electrochemical environment. The electrospun nanofibers were arranged using a drum-type collector, and morphology was investigated using a field emission-scanning electron microscope. The uniformity of dispersion of CNT in the PVDF nanofibers was monitored by electron probe X-ray micro-analysis. Tensile strength and electrical resistivity results were used as an indication of the state of alignment. The electrospun CNT/PVDF nanofiber sheets exhibited better mechanical and electrical properties in the arranged direction. The efficiency and electrical capacities of electrospun CNT/PVDF nanofiber sheet were compared with those of cast PVDF sheets for use in actuator applications in electrochemical environments. The electrospun CNT/PVDF nanofiber sheets exhibited much better actuator performance than PVDF sheets, which are attributed to their superior electrical properties.Highlights(1) The interfacial durability of CNT/PVDF nanofibers was enhanced to increase contact area by reinforcing CNT.(2) The efficiency of CNT/PVDF actuators was improved due to interfacial properties.(3) Thin thickness drum-type collector was made to enhance nanofiber alignment.(4) The arranged CNT/PVDF nanofibers exhibited better mechanical and actuating displacements.

Theoretical model of an optothermal microactuator directly driven by laser beams

This paper proposes a novel method of optothermal microactuation based on single and dual laser beams (spots). The theoretical model of the optothermal temperature distribution of an expansion arm is established and simulated, indicating that the maximum temperature of the arm irradiated by dual laser spots, at the same laser power level, is much lower than that irradiated by one single spot, and thus the risk of burning out and damaging the optothermal microactuator (OTMA) can be effectively avoided. To verify the presented method, a 750 μm long OTMA with a 100 μm wide expansion arm is designed and microfabricated, and single/dual laser beams with a wavelength of 650 nm are adopted to carry out experiments. The experimental results showed that the optothermal deflection of the OTMA under the irradiation of dual laser spots is larger than that under the irradiation of a single spot with the same power, which is in accordance with theoretical prediction. This method of optothermal microactuation may expand the practical applications of microactuators, which serve as critical units in micromechanical devices and micro-opto-electro-mechanical systems (MOEMS).

A review of the hybrid techniques for the fabrication of hard magnetic microactuators based on bonded magnetic powders

Polymer composites based on permanent magnetic bonded powders exhibit immense potential for applications in microactuators and sensors with magnetic performances comparable to their fully dense counterparts. While fabrication and integration of magnetic devices based on bonded magnetic powders is challenging via conventional deposition and electrochemical growth techniques, hybrid fabrication offers a promising alternative. This paper presents the evolution of permanent magnetic materials into bonded magnetic powders, the magnetic performance figures of merit of permanent magnetic materials significant for the design and manufacture of polymer based sensors and actuators. A review of the hybrid fabrication techniques such as replica molding, squeegee coating, spin casting etc are reported. Critical factors affecting the fabrication of polymer magnetic composites such as filler particle size and effect of magnetic field during fabrication are discussed. Prior art based on polymer magnetic composites for the fabrication of hard magnetic films and hard magnetic actuators are presented.

Modeling and inverse compensation of hysteresis in vanadium dioxide using an extended generalized Prandtl–Ishlinskii model

Vanadium dioxide , a promising multifunctional smart material, has shown strong promise in microactuation, memory, and optical applications. During thermally induced insulator-to-metal phase transition of , the changes of its electrical, mechanical, and optical properties demonstrate pronounced, complex hysteresis with respect to the temperature, which presents a challenge in the utilization of this material. In this paper, an extended generalized Prandtl–Ishlinskii model is proposed to model the hysteresis in , where a nonlinear memoryless function is introduced to improve its modeling capability. A novel inverse compensation algorithm for this hysteresis model is developed based on fixed-point iteration with which the convergence conditions of the algorithm are derived. The proposed approach is shown to be effective for modeling and compensating the asymmetric and non-monotonic hysteresis with saturation between the curvature output and the temperature input of a -coated microactuator, as well as the asymmetric hysteresis with partial saturation between the resistance output and the temperature input of a film.

Novel approach to the preparation of organic energetic film for microelectromechanical systems and microactuator applications.

An activated RDX-Fe2O3 xerogel in a Si-microchannel plate (MCP) has been successfully prepared by a novel propylene epoxide-mediated sol-gel method. A decrease of nearly 40 °C in decomposition temperature has been observed compared with the original cyclotrimethylene trinitramine (RDX). The RDX-Fe2O3 xerogel can release gas and solid matter simultaneously, and the ratio of gas to solid can be tailored easily by changing the initial proportions of RDX and FeCl3·6H2O, which significantly enhances the explosive and propulsion effects and is of great benefit to the applications. The approach, which is simple, safe, and fully compatible with MEMS technology, opens a new route to the introduction of organic energetic materials to a silicon substrate.

Controllable high-power, variable-frequency CMOS circuit for microactuator applications

A large-output power, high-current high-voltage, CMOS driving circuit for electrothermal microactuators is presented in this work. The circuit addresses the challenge of providing microelectromechanical systems devices with a monolithic integrated circuit that is capable of outputting high voltage with low output resistance that matches the actuator load for maximum power transfer. The circuit is implemented using a modified eight-stage charge pump. A digital control logic is designed to control the working charge pump stages in order have a variable output voltage between 4 and 15.5 V on a load producing about 150 mW maximum output power. To the authors’ knowledge, the circuit’s output resistance is the lowest among charge pumps that are capable of producing such high voltages. An AC pulse output of 15.5 V amplitude and variable frequency between 60 and 2000 Hz is included in the circuit. The circuit is operated by a conventional 5 V supply. With the variable DC output voltage level and AC output capability, the circuit is suitable for driving many electrothermal microactuators. The total size of the chip excluding pads is 5 mm2.

Functional Response of NiTi Elements for Smart Micro-actuation Applications

Shape memory alloys (SMAs) can be considered a good candidate for actuation applications in the current micro-technology field. In the micro-scale, the temporal response of the SMA actuators can be improved, because of faster cooling during the austenite-martensite transformation. One of the most investigated geometries for this purpose has been the snake-like arrangement, which allows high strokes with considerable forces to be obtained. In this work, SMA elements for micro-actuators were patterned by laser machining in a snake-like shape. Subsequent surface chemical etching was adopted to improve the functional properties of the micro-elements. Calorimetric analysis and thermo-mechanical response of 90 μm thick SMA elements were reported for the evaluation of their functional performances. Moreover, the effect of post-thermal treatment and grain orientation were also evaluated on the final performances.

Photodeformable polymer materials: towards light-driven spoke-type micromotor application

Using a photodeformable polymer material, liquid-crystalline polymer incorporated with azobenzene moieties, a spoke-type micromotor is designed, which could convert light energy directly into mechanical work. It consists of four driving belts, whose mechanical model is established and the driving moment of the micromotor upon irradiation with UV light and without photoirradiation is calculated, respectively. According to the calculated driving moment, the UV light and the visible light are arranged to irradiate from parallel and opposite direction of the micromotor simultaneously, which convert the bending deflection of the photodeformable polymer material belts to continuous rotation of the micromotor. As light is a green energy source that can be controlled remotely, instantly and without the aid of electric wires, the photodeformable polymer material has great potential to be utilized in micro-actuator and other relative applications.

Synthesis and Mechanical Characterization of Magnetic Hybrid Materials with PVB as Polymeric Matrix for Micro-Actuation Applications

ABSTRACTThis work presents two multifunctional magnetic hybrid materials with potential applications as micro-actuators. The first one consists of iron oxide (Fe2O3) nanoparticles embedded in polyvinyl butyral (PVB). For the second one, Fe2O3 nanoparticles, coated with carboxymethyl cellulose (CMC), were embedded in PVB. The main objective is to describe their synthesis and morphological and magnetic characterizations, and to evaluate their displacement against a variable magnetic field. The maximal displacement is obtained by the (Fe2O3-CMC)/PVB beam-shaped structure (28.37 x 2.6 x 0.183 mm3) with 843 μm; the maximal electric power being 1.14 W. The levels of displacement induced in both hybrid materials as a response of the external magnetic field, besides the low electric power required, let us conclude that the studied materials could be considered as good candidates to micro-actuators applications.

Strain-enhanced Nanocomposites of Electrostrictive Polymers and High-k Nanofillers for Micro-actuation Applications

Abstract This paper reports on nanocomposites of enhanced field induced strain based on an electrostrictive polymer mixed with BaTiO 3 and TiO 2 nanofillers of high dielectric constants. Nanocomposite thin film bimorph actuator stacks were optimized with respect to the nanofiller homogeneous dispersion and thin film surface roughness upon film annealing. The investigations showed that the nanocomposite properties are strongly dependent on the nanofiller content, nanoparticle size and relative permittivity. By the addition of nanofillers, the electro-mechanical properties of the polymer matrix have been significantly improved. Particularly, we obtained increased permittivity to about 44 and about two-fold larger strain for a 2 wt% BaTiO 3 nanocomposite and a 1.4 times larger strain for a 10 wt% TiO 2 nanocomposite. FEM simulations indicate that nanocomposite based bending actuators can exhibit remarkably large deformation.

Interfacial durability and electrical properties of CNT or ITO/PVDF nanocomposites for self-sensor and micro actuator applications

Interfacial durability and electrical properties of CNT (carbon nanotube) or ITO (indium tin oxide) coated PVDF (poly(vinylidene fluoride)) nanocomposites were investigated for self-sensor and micro-actuator applications. The electrical resistivity of nanocomposites and the durability of interfacial adhesion were measured using a four points method during cyclic fatigue loading. Although the CNT/PVDF nanocomposites exhibited lower electrical resistivity due to the inherently low resistivity of CNT, both composite types showed good self-sensing performance. The durability of the adhesion at the interface was also good for both CNT and ITO/PVDF nanocomposites. Static contact angle, surface energy, work of adhesion, and spreading coefficient between either CNT or ITO and PVDF were determined as checks to verify the durability of the interfacial adhesion. The actuation performance of CNT or ITO coated PVDF specimens was determined through measurements of the induced displacement using a laser displacement sensor, while both the frequency and voltage were changed. The displacement of these actuated nanocomposites increased with increasing voltage and decreased with increasing frequency. CNT/PVDF nanocomposites exhibited better performance as self-sensors and micro-actuators than did ITO/PVDF nanocomposites.

Enhancing magnetocrystalline anisotropy of the Fe70Pd30 magnetic shape memory alloy by adding Cu

Fe–Pd–Cu thin films are of great interest for applications in magnetic shape memory microsystems due to their increased martensitic transformation temperature. Here we analyse the consequences of Cu addition to Fe–Pd on the binding energy and magnetic properties by a combination of thin film experiments and first-principles calculations. Strained epitaxial growth of Fe70Pd30-xCux with x=0,3,7 is used to freeze intermediate stages during the martensitic transformation. This makes a large range of tetragonal distortion susceptible for analysis, ranging from body-centred cubic to beyond face-centred cubic (1.07<c/abct<1.57). We find that Cu enhances the quality of epitaxial growth, while spontaneous polarization and Curie temperature are reduced only moderately, in agreement with our calculations. Beyond c/abct>1.41 the samples undergo structural relaxations through adaptive nanotwinning. Cu enhances the magnetocrystalline anisotropy constant K1 at room temperature, which reaches a maximum of −2.4×105Jm−3 around c/abct=1.33. This value exceeds those of binary Fe70Pd30 and the prototype Ni–Mn–Ga magnetic shape memory system. Since K1 represents the maximum driving energy for variant reorientation in magnetic shape memory systems, we conclude that Fe–Pd–Cu alloys offer a promising route towards microactuator applications with significantly improved work output.

Understanding the Magnetic Shape Memory System Fe–Pd–X by Thin Film Experiments and First Principle Calculations

AbstractThe magnetic shape memory (MSM) alloy Fe70Pd30 is of particular interest for novel microactuator and sensor applications. This review summarizes the underlying physical and material science concepts for this MSM alloy system. First‐principles calculations of the electronic and crystallographic structure together with combinatorial and epitaxial film studies are presented. By these complementary methods we can address the open key questions of MSM alloys and microsystems: Which are the driving forces for a martensitic transformation and how does this transformation proceed? How is it possible to improve the MSM properties by adding third elements? What is the role of external interfaces and which routes allow the preparation of freestanding epitaxial films?

Magnetically Actuated Artificial Cilia as Microfluidic Mixers

The absence of turbulence is a hallmark of fluid flow in the microfluidic regime, and so mixing is difficult to accomplish. Approaches to microfluidic mixing have varied widely, from passive devices which encourage complex flow with various modifications of the channel geometry to active mixers actuated by electric or magnetic fields. An ideal active mixer would be small enough to fit inside the narrowest microfluidic geometries and easily manipulated by external fields. We present here a novel material which is a composite of magnetic nanoparticles and silicone polymer. This material has a high magnetic content (up to 50% wt.) and is homogenous at length scales below 100 nm, making it ideally suited to the fabrication of micro-scale mixing devices. We optimize this material for use in microactuator applications and demonstrate a protocol for fabricating micro-mixers similar in scale to biological cilia (25 microns in length by 1 micron in diameter). A large array of these mixers may be fabricated within the confines of a microfluidics channel and actuated via an external magnetic field from a permanent magnet.

Physical approaches to the design of microactuators for micro- and nanopositioning: The information aspect

Microactuators are an important tool for precise manipulation of components and materials in nanotechnologies. The problems of design and application of microactuators for micro- and nanopositioning, microassembly, and microrobotics are considered in this paper. The basic parameters and models of piezoelectric, magnetostriction, electromagnetic, electrostatic, electrothermal, and hybrid microactuators are described. A general information approach that implies the description of physical models used in order to analyze microactuator behavior and optimize their design is considered.

Control of Paste Rheology and Piezoelectric Properties of Bi0.5(Na0.82K0.18)0.5TiO3 Lead-Free Piezoelectric Thick Films Deposited by Screen Printing

Bi0.5(Na0.82K0.18)0.5TiO3 (NKBT) lead-free thick films with a thickness of 10–100 μm have been deposited on a Pt-electroded alumina substrate using screen printing. The influences of the NKBT particle size, NKBT powder content, binder concentration, and dispersant on the rheological characteristics were systematically investigated. The resulting 60 μm thick films exhibit a dielectric constant of 582 (10 kHz), a dielectric loss of 2.8%, remanent polarization of 22.5 μC/cm2, a coercive field of 62 kV/cm, and a longitudinal effective piezoelectric coefficient, d33eff of 91 pm/V. The thick films are expected to be a new and promising candidate for lead-free piezoelectric microdevices especially the microactuator applications.

Low Cost and High Resolution X-Ray Lithography for Fabrication of Microactuator

In this work, low-cost and high resolution X-ray lithography is developed by employing low-cost sputtered lift-off lead film on mylar sheet substrate and applied for fabrication of electrostatic actuators. X-ray mask was fabricated by conventional photolithography, Pb sputtering and lift-off process. The Pb mask is used for X-ray lithography of electrostatic actuator structures with 5 µm interdigitate electrodes. For 140 µm-thick SU-8 photoresist on Cr-coated glass substrates, Pb film thickness of around 10 µm was used to block X-ray with 95% x-ray image contrast at a critical dose of 4,200mJ/cm3. A high aspect ratio of 26.5 of SU8 microstructure with 5 µm lateral resolution has been achieved by the developed low cost Pb based X-ray mask. In addition, a steep sidewall angle of nearly 90o for SU-8 structure is confirmed. The results demonstrate that the Pb based X-ray mask offers high resolution X-ray lithography at a very low cost and is promising for microactuator applications.