Yongjun Lai

Performance characterization of in-plane electro-thermally driven linear microactuators

Static and dynamic electro-mechanical performance of a microactuator is a key factor in the functioning of an integrated microsystem composed of moving components such as optical shutters/switches, micropumps, microgrippers, and microvalves. Therefore, the development of such systems primarily focuses on the overall design and parameter optimization of an actuator as the major driving element with respect to the desired performance parameters, e.g., displacement, force, dimensional constraints, material, actuation principle, and method of fabrication. This study presents results on the static and dynamic electro-mechanical performance analysis of an in-plane electro-thermally driven linear microactuator. Each microactuator, having a width of 2220 mm and made of 25 mm thick nickel foil, consisted of a pair of cascaded structures. Connecting several actuation units in a series formed each cascaded structure. Several microactuators with a different number of actuation units were fabricated using the laser micromachining technology. The static performance of these microactuators was evaluated with respect to the maximum linear output displacements, actual resistance, applied current, and consumed electric power. The maximum displacements varied approximately from 3 to 44 mm, respectively, depending on the number of actuation units. The dynamic performance was studied as a response function on constant applied current with respect to the output displacements. In addition, the response time was evaluated for different applied currents and for actuators with 2, 4, and 6 actuation units. The microactuators’ performance results are promising for applications in MEMS/MOEMS, microfluidic, and microrobotic devices.

Design of an electrostatic MEMS microgripper system integrated with force sensor

This work presents the design of a microgripper integrated with force sensor using electrostatic actuation. The single capacitance sensor used in the design can also operate as an actuator when force sensing is not required. The design is optimized in the standard MEMS technology SOIMUMPs. An input voltage of 85 V produces a force of 384 ¿N and a displacement of 15 ¿m. In dual actuation mode, the gripper jaws are displaced 15 ¿m at an input voltage of 60 V. A concept of two stage jaw is given which increases the range of object size gripped to 30 ¿m without increasing the size or input voltage of the actuator.

Size-variable droplet actuation by interdigitated electrowetting electrode

We propose electrowetting on dielectric (EWOD) electrodes to actuate size-variable droplets. By using interdigitated fingers and maximizing them in optimized construction, we can control droplets in different sizes with the same electrode array automatically. We both do the theory calculation and experiment verification to study the electrode with rectangular fingers. It is found that the electrode with triangle fingers can actuate droplets as small as 1/36 of that actuated by conventional square electrode array. It can actuate large droplets more efficiently than rectangular fingers. This work provides an approach to achieve multifunctional EWOD devices in the future.

Thermal Actuation Based 3-DoF Non-Resonant Microgyroscope Using MetalMUMPs.

High force, large displacement and low voltage consumption are a primary concern for microgyroscopes. The chevron-shaped thermal actuators are unique in terms of high force generation combined with the large displacements at a low operating voltage in comparison with traditional electrostatic actuators. A Nickel based 3-DoF micromachined gyroscope comprising 2-DoF drive mode and 1-DoF sense mode oscillator utilizing the chevron-shaped thermal actuators is presented here. Analytical derivations and finite element simulations are carried out to predict the performance of the proposed device using the thermo-physical properties of electroplated nickel. The device sensitivity is improved by utilizing the dynamical amplification of the oscillation in 2-DoF drive mode using an active-passive mass configuration. A comprehensive theoretical description, dynamics and mechanical design considerations of the proposed gyroscopes model are discussed in detail. Parametric optimization of gyroscope, its prototype modeling and fabrication using MetalMUMPs has also been investigated. Dynamic transient simulation results predicted that the sense mass of the proposed device achieved a drive displacement of 4.1μm when a sinusoidal voltage of 0.5V is applied at 1.77 kHz exhibiting a mechanical sensitivity of 1.7μm /°/s in vacuum. The wide bandwidth frequency response of the 2-DoF drive mode oscillator consists of two resonant peaks and a flat region of 2.11 kHz between the peaks defining the operational frequency region. The sense mode resonant frequency can lie anywhere within this region and therefore the amplitude of the response is insensitive to structural parameter variations, enhancing device robustness against such variations. The proposed device has a size of 2.2 × 2.6 mm2, almost one third in comparison with existing M-DoF vibratory gyroscope with an estimated power consumption of 0.26 Watts. These predicted results illustrate that the chevron-shaped thermal actuator has a large voltage-stroke ratio shifting the paradigm in MEMS gyroscope design from the traditional interdigitated comb drive electrostatic actuator. These actuators have low damping compared to electrostatic comb drive actuators which may result in high quality factor microgyroscopes operating at atmospheric pressure.

Development of a bidirectional ring thermal actuator

A new planar micro electrothermal actuator capable of bidirectional rotation is presented. The ring thermal actuator has a wheel-like geometry with eight arms connecting an outer ring to a central hub. Thermal expansion of the arms results in a rotation of the outer ring about its center. An analytical model is developed for the electrothermal and thermal–mechanical aspects of the actuators operation. Finite element analysis is used to validate the analytic study. The actuator has been fabricated using the multi-user MEMS process and experimental displacement results are compared with model predictions. Experiments show a possible displacement of 7.4 µm in each direction. Also, by switching the current between the arms it is possible to achieve an oscillating motion.

Modal Simulation and Testing of a Micro-Manipulator

A micro-machined manipulator with three kinematic degrees-of,freedom (DOF): x, y, and φ is presented. The manipulator is driven by three thermal actuators. A six DOF discrete spring-mass model of the compliant mechanism is developed which manifests the dynamic properties of the device. Numerical simulations are compared with experimental results.

Comparative analysis of microactuators fabricated by femtosecond and nanosecond laser micromachining

Laser micromachining technology is a cost-effective microfabrication technique for prototyping and in some cases batch production of miniature components and microdevices with complex geometries requiring high accuracy and precision. The objective of this paper is to analyze experimentally the effect of the laser micromachining process and its parameters, particularly, the pulse duration, on the characteristics of the fabricated functional microdevices. This was achieved through the microfabrication of two electro-thermally driven in-plane microactuators using a femtosecond and a nanosecond pulse laser. The dynamic/static performance of the microactuators was compared with respect to the required current/power and generated actuation force/displacement and the geometric quality of the machining.

Comparative Study on Finite Element Analysis & System Model Extraction for Non-Resonant 3-DoF Microgyroscope

This paper reports a comparative study of full transient start up analysis of a Non-Resonant Micromachined Gyroscope using Finite Element Analysis (FEA) and System Model Extraction (SME) techniques. FEA is a popular numerical technique based on Finite Element Method (FEM) for carrying out different engineering analyses. But one of the major disadvantages of this FEA is its computational time. While running multiple optimization analyses with a FE Solver, it may take days, weeks and possibly months depending on extent of optimization. In this study we initially analyzed the MEMS based microgyro on a device level using FEM. We determined the natural frequencies of the gyro along with the both static and dynamic responses of the gyro. After these device level simulations in FEA we switched to the system level simulation. Using SME we generated system model of the gyro with system level components and run a full transient startup response analysis of the device by incorporating that extracted model in INTELLISUITE circuit simulator SYNPLE. When we compared the computational time required by both techniques, we found that SME with SYNPLE is orders of magnitude faster than FEA.

3D stepped electrodes on a flexible substrate with permanently bonded poly(dimethylsiloxane) channels for moving microfluid

Interdigitated microelectrode arrays have been exploited to move electrolyte via ac electro-osmosis. The performance of three dimensional (3D) stepped electrodes has been shown to exceed that of planar electrodes. However, to date all prototypes described have been based on solid silicon or glass substrates, limiting the usage of such devices. This report, to our best knowledge, is the first to describe a 3D stepped microelectrode array on a flexible Kapton® substrate. The Kapton surface was modified to make it capable of bonding with poly(dimethylsiloxane) microchannels. The metal electrode was patterned by wet etching, a simpler process than previous approaches. Results of bonding, bending, and fluidic testing are reported. The frequency response obtained using deionized water showed maximum velocities of approximately 370 and 180 μm/s at 5Vpp for testing with a flat and bent substrate, respectively.

AC electroosmotic micropumping with a square spiral microelectrode array

An electro-kinetic micropumping device has been designed, experimentally tested and analyzed theoretically using coupled computational fluid dynamic and electrostatic simulations. A microelectrode array uses the principle of AC electroosmosis; bulk fluid motion due to ions driven along microelectrode surfaces by forces stemming from tangential electric fields. Three submerged microelectrode wires, deposited to form a square spiral, had a three-phase traveling-wave applied AC signal to create a net flow. Microsphere tracers were used to measure the flow to determine pumping performance, and compare the fluid velocity and operating frequency to theoretical results. The device presented here demonstrated bi-directional pumping capabilities and the potential for use as both a particle collector and microfluidic pump.