Electrothermal Actuator Design Research Articles

Performance Analysis of a CSFH-Based Microgripper: Analytical Modeling and Simulation.

Microgrippers are promising tools for micro-manipulation and characterization of cells. In this paper, a biocompatible electro-thermally actuated microgripper with rotary capacitive position sensor is presented. To overcome the limited displacement possibilities usually provided by electrothermal actuators and to achieve the desired tweezers output displacement, conjugate surface flexure hinges (CSFH) are adopted. The microgripper herein reported can in principle manipulate biological samples in the size range between 15 and 120 µm. A kinematics modeling approach based on the pseudo-rigid-body-method (PRBM) is applied to describe the microgripper’s working mechanism, and analytical modeling, based on finite elements method (FEM), is used to optimize the electrothermal actuator design and the heat dissipation mechanism. Finally, FEM-based simulations are carried out to verify the microgripper, the electrothermal actuator and heat dissipation mechanism performance, and to assess the validity of the analytical modeling.

Three-Layered Design of Electrothermal Actuators for Minimal Voltage Operation.

By designing an actuator composed of thin layers with different coefficients of thermal expansion (CTE) together with an electrically conductive layer, the CTE mismatch can be utilized to produce soft electrothermal actuators (ETAs). These actuators have been typically implemented using only two layers, commonly relying on Timoshenko's analytic model that correlates the temperature to the actuator's curvature. In this study, we extend the analytic model to include the thermoelectric relation present in ETAs, that is, the conductive layer's properties with respect to the operation temperature. By applying the thermoelectric relation, a minimal voltage optimization can be applied to the analytic model. Using dimensionless analysis, we optimize the ETAs performance for both bi- and tri-layer ETAs with and without the thermal modeling. The bi-layer optimization not only predicts the maximal value for the bi-layer performance but also provides the optimal thickness of each layer for any couple of materials. We validate the tri-layer analytic model experimentally by measuring the curvature for different third layer thicknesses. Finally, we optimize the tri-layer design based on the analytic model, which can achieve an improvement in curvature per voltage of >3000% over the optimal bi-layer ETA.

A Millimeter-Tunable-Range Microlens for Endoscopic Biomedical Imaging Applications

We report an electrothermally-actuated microlens scanner that is suitable for biomedical imaging applications. The microlens has a large tunable range and a low driving voltage, and the lens is made of glass. The enabling device is a new electrothermal actuator design that is capable of large vertical actuation (~0.9 mm) on a 3 mm device footprint, with small lateral shift (<; 7 μm) and tilting (<; 0.38°) at less than 4-V. The design, fabrication and characterization of the actuator are presented. Imaging results by the assembled microlens are also demonstrated.

A large vertical displacement electrothermal bimorph microactuator with very small lateral shift

This paper reports a novel electrothermal actuator design that can generate large vertical displacements with almost no lateral shift. The lateral-shift-free (LSF) piston motion is achieved by using a unique three-bimorph actuation mechanism. Both micromirrors and microlens holders based on this new actuator design have been fabricated using a combined surface- and bulk-micromachining process. A 0.62mm vertical displacement is measured at only 5.3V for a fabricated 0.8mm by 0.8mm micromirror, and both the lateral shift (10μm) and tilting angle (0.7°) are very small in that full vertical displacement range. The measured resonant frequency of the vertical motion mode is about 0.5KHz. The thermal response time is about 25ms.

Modelling & Simulation of Novel Three Arm MEMS Actuators & Its Application

This paper presents the design and Finite Element Model (FEM) simulation of a novel electrothermal microactuators and arrays. It is a single material microactuator which deflects at its tips by differential thermal expansion of its constituent parts. The electrothermal actuator consists of three thin arms, three thin blades and two electrical connection pads. The goal of this coupled electrothermal actuator design was to multiply the force by adding the individual contributions of all the three actuators. The difference in magnitude of blade deflections depends on the geometrical characteristics of the actuators. The thermal deformation and thermal stability are easily controllable. The simulation employing ANSYS/Multiphysics software results include force, deflection, thermal stress, ideal electrothermal actuator and array geometries. The main advantage of this electrothermal actuator is large deflection of blades with very low actuation voltage in comparison with electrostatic actuators. A typical application in a micromirror is shown to illustrate the utility of these actuators and arrays.

Design and performance of an electrothermal MEMS microengine capable of bi-directional motion

Several microactuator technologies have been investigated for positioning individual elements in large-scale microelectromechanical systems (MEMS). Electrostatic, magnetostatic, piezoelectric and thermal expansion represent the most common modes of microactuator operation. This research focuses on the design and comparative performance evaluation of asymmetrical electrothermal actuators. The motivation is to present a unified description of the behavior of the electrothermal actuator so that it can be adapted to a variety of microsensor and microactuator applications. The MEMS polysilicon surface micromachined electrothermal actuator uses resistive (Joule) heating to generate thermal expansion and movement. In the traditional asymmetrical electrothermal actuator design, the single-hot arm is narrower than the cold arm, and thus, the electrical resistance of the hot arm is greater. When an electrical current passes through the device (both the hot and cold arms), the hot arm is heated to a higher temperature than the cold arm. This temperature differential causes the hot arm to expand along its length, thus forcing the tip of the device to rotate about the flexure. Another variant of the asymmetrical design features a double-hot arm arrangement that eliminates the parasitic electrical resistance of the cold arm. Furthermore, the second hot arm improves electromechanical efficiency by providing a return current conductor that is also mechanically active. In this design, the rotating cold arm can have a narrower flexure compared to the flexure in the traditional single-hot arm device because it no longer needs to conduct an electrical current. The narrower flexure results in an improvement in mechanical efficiency. This research compares the tip deflection performance of the asymmetrical single- and double-hot arm electrothermal actuator designs. Deflection measurements of both actuator designs as a function of arm length and applied electrical power are presented. As a practical application of the electrothermal actuator, the recent realization of a MEMS microengine is described, and evidence of its bi-directional motion is presented. The electrothermal actuator and microengine designs were accomplished with the MEMSPro® CAD software program, and they were fabricated using the MEMSCAP Integrated Microsystems Multi-User Microelectromechanical Systems (MEMS) Process® (MUMPs) foundry.

Design and performance of an electrothermal MEMS microengine capable of bi-directional motion

Several microactuator technologies have been investigated for positioning individual elements in large-scale microelectromechanical systems (MEMS). Electrostatic, magnetostatic, piezoelectric and thermal expansion represent the most common modes of microactuator operation. This research focuses on the design and comparative performance evaluation of asymmetrical electrothermal actuators. The motivation is to present a unified description of the behavior of the electrothermal actuator so that it can be adapted to a variety of microsensor and microactuator applications. The MEMS polysilicon surface micromachined electrothermal actuator uses resistive (Joule) heating to generate thermal expansion and movement. In the traditional asymmetrical electrothermal actuator design, the single-hot arm is narrower than the cold arm, and thus, the electrical resistance of the hot arm is greater. When an electrical current passes through the device (both the hot and cold arms), the hot arm is heated to a higher temperature than the cold arm. This temperature differential causes the hot arm to expand along its length, thus forcing the tip of the device to rotate about the flexure. Another variant of the asymmetrical design features a double-hot arm arrangement that eliminates the parasitic electrical resistance of the cold arm. Furthermore, the second hot arm improves electromechanical efficiency by providing a return current conductor that is also mechanically active. In this design, the rotating cold arm can have a narrower flexure compared to the flexure in the traditional single-hot arm device because it no longer needs to conduct an electrical current. The narrower flexure results in an improvement in mechanical efficiency. This research compares the tip deflection performance of the asymmetrical single- and double-hot arm electrothermal actuator designs. Deflection measurements of both actuator designs as a function of arm length and applied electrical power are presented. As a practical application of the electrothermal actuator, the recent realization of a MEMS microengine is described, and evidence of its bi-directional motion is presented. The electrothermal actuator and microengine designs were accomplished with the MEMSPro ® CAD software program, and they were fabricated using the MEMSCAP Integrated Microsystems Multi-User Microelectromechanical Systems (MEMS) Process ® (MUMPs) foundry.

Single- and double-hot arm asymmetrical polysilicon surface micromachined electrothermal microactuators applied to realize a microengine

This research focuses on the design and experimental characterization of two types of MEMS asymmetrical electrothermal microactuators. The motivation is to present a description of the behavior of the electrothermal microactuator to facilitate its adaptation to a variety of MEMS applications. Both MEMS polysilicon electrothermal microactuator design variants use resistive (Joule) heating to generate thermal expansion and movement. In a conventional electrothermal microactuator, the ‘hot’ arm is positioned parallel to a ‘cold’ arm, but since the ‘hot’ arm is narrower than the ‘cold’ arm, the electrical resistance of the ‘hot’ arm is larger. When an electrical current passes through the microactuator (through the series connected electrical resistance of the ‘hot’ and ‘cold’ arms), the ‘hot’ arm is heated to a higher temperature than the ‘cold’ arm. This temperature increase causes the ‘hot’ arm to expand along its length, thus forcing the tip of the device to rotate about a mechanical flexure element. A new electrothermal actuator design eliminates the parasitic electrical resistance of the ‘cold’ arm by incorporating an additional ‘hot’ arm. The second ‘hot’ arm results in an improvement in electrical efficiency by providing an active return current path. Additionally, the ‘cold’ arm can now have a narrower flexure compared with the conventional single-‘hot’ arm device because it does not have to pass an electric current. A narrower flexure element manifests improved mechanical efficiency. Deflection and force measurements of both electrothermal actuators as a function of applied electrical power are presented. Also described is the practical integration of the electrothermal microactuators in a monolithic microengine that is capable of rotating a set of gears.