Types Of Microactuators Research Articles

Quasi-Static Pull-in: an Instability in Electrostatic Actuators

We identify a new instability in electrostatic actuators dubbed quasi-static pull-in. We report experimental evidence of the instability and study its characteristics in two types of micro actuators operating in ambient air. We found that the underlying mechanism is a fast-slow dynamic interaction between slowly-varying electrostatic excitation and fast resonator response that instigate large non-resonant oscillatory orbits and eventually disappears in a global Shilnikov bifurcation. Based on these findings, we formulate and present a new taxonomy of pull-in instabilities in electrostatic actuators.

Thermal behavior modeling and characteristics analysis of electrothermal microactuators

Electrothermal microactuators possess a number of desirable attributes including ease of fabrication and large force and displacement capabilities relative to other types of microactuators, but these performances come at the expense of large input energy and relatively low frequencies because of the time necessary to reach thermal equilibrium. These characteristics provide motivation for improving thermal actuator designs that are more energy efficient and better suited for high-frequency applications. To this end, models describing the combined electrothermal and thermomechanical behavior of thermal actuators are developed in this thesis. The temperature distribution of the actuator is analyzed and the influence of the actuator’s geometrical parameters on its force and displacement is studied. Steady-state and transient thermal responses of the actuator operating in air and a vacuum are investigated by creating finite-difference model with temperature-dependent parameters, this model allows temperatures throughout the actuator to be simulated as a function of time. Results demonstrate that the efficiency of the actuator can be improved significantly by operating in a vacuum environment and providing short-duration, high-current pulse inputs. A set of parametric studies and design changes are evaluated through thermomechanical models, strategies gained from modeling analysis result in significant improvements in operational efficiency of the thermal actuator.

Velocity field measurements on high-frequency, supersonic microactuators

The resonance-enhanced microjet actuator which was developed at the Advanced Aero-Propulsion Laboratory at Florida State University is a fluidic-based device that produces pulsed, supersonic microjets by utilizing a number of microscale, flow-acoustic resonance phenomena. The microactuator used in this study consists of an underexpanded source jet that flows into a cylindrical cavity with a single, 1-mm-diameter exhaust orifice through which an unsteady, supersonic jet issues at a resonant frequency of 7 kHz. The flowfields of a 1-mm underexpanded free jet and the microactuator are studied in detail using high-magnification, phase-locked flow visualizations (microschlieren) and two-component particle image velocimetry. These are the first direct measurements of the velocity fields produced by such actuators. Comparisons are made between the flow visualizations and the velocity field measurements. The results clearly show that the microactuator produces pulsed, supersonic jets with velocities exceeding 400 m/s for roughly 60 % of their cycles. With high unsteady momentum output, this type of microactuator has potential in a range of ow control applications.

High reliability nanosandwiched Pt/Ti multilayer electrode actuators for on-chip biomedical applications

Microactuators provide the main driving force for fluid pumping in microfluidic devices and thus play an important role in on-chip biomedical applications. Interdigitated electrode based electrochemical actuators have provided a viable choice for effective actuation with advantages of flexible controllability, biocompatibility and ease of fabrication. However, the current feature size of a typical electrode structure is around 100 μm, which is relatively large for device miniaturization and integration. Further decrease in the feature size will lead to dramatic decrease in the reliability and lifetime of the actuators, caused by metal delamination. In this work, we propose a novel design of electrodes to fabricate a new type of microactuator with high reliability. To prevent the occurrence of delamination, a nanosandwiched multilayer structure of titanium/platinum is used to construct the conductive metal layer for the interdigitated electrodes. The feature size of the electrodes is greatly reduced to 20 μm where we have reduced the size by 80% of the similar structures reported previously. At the same time, the lifetime of the new electrodes has been dramatically increased to over 400% as compared to the conventional design. With these remarkable improvements in the electrode design, we have fabricated a prototype microfluidic device integrating the new microactuator for drug tests in cancer therapy, demonstrating its usefulness for on-chip biomedical applications.

Switching Time Reduction for Electrostatic Torsional Micromirrors Using Input Shaping

We have demonstrated switching time reduction for microfabricated, vertical comb-based electrostatic torsional micromirror actuators by suppressing residual vibration using pre-shaped command inputs. The step input is pre-shaped by pulse–impulse convolution method, one of the impulse shaping filters. The micromirror actuators tested in experiment are made of single-crystal silicon and driven by vertical comb sets in torsional direction. Before shaping the input signal, the measured 2% settling time is 25 ms with percent overshoot of 58% for a step voltage input to induce the angular motion in micromirror actuator. The improved settling time is observed to be 8 ms with 5.8% overshoot when the pre-shaped input is applied. The input-shaping technique is applied to two types of microactuators with different dynamic characteristics in order to verify its feasibility on various systems, and it is experimentally shown that the pre-shaped input command successfully suppresses the residual vibration for both highly underdamped microactuators.

Solution of nonlinear pull-in behavior in electrostatic micro-actuators by using He’s homotopy perturbation method

The work presented here is about the nonlinear pull-in behavior of different electrostatic micro-actuators. He’s homotopy perturbation method (HPM) is applied to solve different types of micro-actuators like Fixed–Fixed beam and Cantilever beam actuators. Simulated results are presented for further analysis. Also the obtained results compare well with the literature.

Suppression of Martensitic Phase Transformation, Shape Memory and High Damping by Ion Implantation in Ni-Ti Thin Films

The shape memory effect and the high damping in shape memory alloys are based on the martensitic phase transformation, which takes place essentially without diffusion and any change of order have an influence on its side effects: the memory effect, the superelasticity and the high damping capacity of the martensitic phase. A new method to control the performance of shape memory alloys is presented, which is based on selective modification of specified parts of working components. In this research, ion irradiation has been used to introduce locally disorder into a crystal or even amorphise it. A pre-deformed Ni-Ti, 6μm thin film in its martensitic state has been irradiated with Ni-ions of energy of 5 MeV up to a dose of 1016 ions/cm2. By this treatment, a 2μm thin surface layer has been finally transformed into an amorphous state, in which the martensitic transformation is suppressed. During heating the underlying non-modified layer is contracting and an out-of-plane movement is observed. The amorphous layer is elastically deformed and its energy is used during cooling to bring the film in its original shape. In this way, a reversible movement of the film is created. This new technique not only allows us to design new types of micro-actuators, but also to influence locally the high damping, which can be of great importance for micro-engineering applications.

Adomian decomposition method used for solving nonlinear pull-in behavior in electrostatic micro-actuators

Nonlinear pull-in behavior for different electrostatic micro-actuators were simulated in this study. The Adomian decomposition method was employed to overcome the difficulty in the nonlinear equation of motion. Because no iteration is required in solving the nonlinear deformation, the decomposition method is one of the most efficient methods for evaluating the unstable pull-in behavior of an electrostatic micro-actuator. To investigate the feasibility of applying the Adomian decomposition method in dealing with the nonlinear deflection equation in the micro-actuator problem, different types of micro-actuators, e.g., fixed-fixed beam actuator and cantilever beam actuator were studied and analyzed. The calculated results agreed well with those from the literature.

Polymeric magnetic microactuator with efficient permalloy loop design

In the study, two types of polyimide (PI) magnetic microactuator with different geometries were designed, fabricated and tested. Mathematic model is created by ANSYS software to design the two microactuators, respectively. The magnetic field generated by the planar coil with permalloy circuit loop design was simulated by ANSYS software. The simulation result shows that the magnetic force can be up to 34.69 mN. Fabrication of the electromagnetic microactuator combines with 10 μm thick Ni/Fe (80/20) permalloy circuit loop deposition, 10 μm thick permalloy plate with 800 × 800 μm in area on PI diaphragm, high aspect ratio electroplating of copper planar coil with 10 μm in thickness, bulk micromachining, and excimer laser ablation. They were fabricated by a novel concept avoiding the etching selectivity and residual stress problems during wafer etching. First, PI diaphragm with micro-electroplated Ni/Fe permalloy was released by anisotropic wet etching, followed by mask projection of 248 nm excimer laser ablation. The new concept of excimer laser ablation process demonstrates that microstructure can be post-ablated after bulk micromachining. By applying a current through planar coil, the PI diaphragm will be actuated. ANSYS software was used to predict the deflection angle of the two types of microactuators. The preliminary theoretical simulation shows a good agreement with experimental result.

Modeling the thermal behavior of a surface-micromachined linear-displacement thermomechanical microactuator

Thermomechanical microactuators possess a number of desirable attributes including ease of fabrication and large force and displacement capabilities relative to other types of microactuators. These advantages provide motivation for improving thermomechanical microactuator designs that are more energy efficient and thus better suited for low-power applications. To this end, this paper describes the development and experimental validation of a finite-difference thermal model of a thermomechanical in-plane microactuator (TIM). Comparisons between the model and experimental results demonstrate the importance of including the temperature dependence of several parameters in the model. Strategies for reducing the power and energy requirements of the TIM were investigated using model simulations as a guide. Based on design insights gained from the model, the energy efficiency of the TIM has been improved significantly by operating in a vacuum environment and providing short-duration, high-current pulse inputs. These improvements have been validated experimentally.

Design and control of a pneumatic microrobot for in-pipe inspection of nuclear pipes

Micro Electro Mechanical Systems (MEMS) are integrated in many current products and are not only the concern of military defence or medicine. Nowadays, many different types of microactuators exist which use different types of energy and perform a variety of movements. Several applications require small systems to inspect confined and hostile places. Vapour generators in nuclear plants comprise of 3000 to 5000 vertical pipes of 17 mm diameter. These pipes endure high mechanical constraints and have to be inspected to detect possible cracks. Our study is based on the design, modelling and implementation of a microrobot able to move upwards within and carry sensors into these pipes. It moves as an inchworm and is composed of 2 blocking modules that brace the robot on the pipe sides, and one stretching module that creates a step. This actuator is pneumatic and composed of metal bellows. By this original design, the microrobot has a good power-to-volume ratio and it can carry a load of 600 g. Its good positioning accuracy has been proved over a 90 mm course where the error of positioning is less than 60 μm.

Automatic adjustment of monomode optical waveguides by a microsystem

An integrated microsystem is being developed which is able to handle the tight mechanical tolerances of monomode waveguide couplings by a controlled adjustment movement. It basically contains a two-axis microactuator for moving a fibre or a microlens, an optical sensor for the position detection, and a control circuit. Two types of microactuators, made completely by silicon micromachining, are investigated. The piezoelectric version contains a compliant mechanism with a two-stage hinge gear in order to enlarge the movement range. The electromagnetic system consists of several planar coils enabling bi-directional actuation. Both actuators easily cover an x - y displacement range of . As for position sensing, the most promising results are reached by detecting cladding modes resulting in a sharp signal minimum at the optimum position. The control algorithm is carried out by a microprocessor.

Controlled Folding of Micrometer-Size Structures

Several types of microactuators have been fabricated, from simple paddles to self-assembling and -disassembling cubes. Conducting bilayers made of a layer of polymer and a layer of gold were used as hinges to connect rigid plates to each other and to a silicon substrate. The bending of the hinges was electrically controlled and reversible, allowing precise three-dimensional positioning of the plates. The structures were released from the substrate with a technique based on differential adhesion. This method, which avoids the use of a sacrificial layer and allows the actuators to pull themselves off the surface, may have general applications in micromachining. Possibilities include the manufacture, of surfaces whose light reflection or chemical properties can be switched.

Recent progress of microactuators and micromotors

This paper gives a concise review of IC-compatible micromachining technologies and various types of microactuators fabricated by such technologies. A system architecture oriented to micro systems is proposed. Promising fields of application are briefly overviewed.