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This paper presents a new model and test device for determining piezoresistive response in long, thin polysilicon beams with axial and bending moment inducing loads. If the piezoresistive coefficients are known, the Integrated Piezoresistive Flexure Model (IPFM) is used to find the new resistance of a beam under stress. The IPFM first discretizes the beam into small volumes represented by resistors. The stress that each of these volumes experiences is calculated, and the stress is used to change the resistance of the representative resistors according to a second-order piezoresistive equation. Once the resistance change in each resistor is calculated, they are combined in parallel and series to find the resistance change of the entire beam. If the piezoresitive coefficients are not initially known, data are first collected from a test device. Piezoresistive coefficients need to be estimated and the IPFM is run for the test device’s different stress states giving resistance predictions. Optimization is done until changing the piezoresistive coefficients provides model predictions that accurately match experimental data. These piezoresistive coefficients can then be used to design and optimize other piezoresistive devices. A sensor is optimized using this method and is found to increase voltage response by an estimated 10 times.

This paper presents an underwater, silicon, thermal microactuation system capable of moving a 200 μN load to a displacement of 110 μm. Its function relies on a thermal actuator capable of 9 μm of displacement in an aqueous environment. This actuator is combined with a ratcheting device to achieve the 110 μm of displacement. The system is a microelectromechanical system (MEMS) fabricated with a two layer surface-micromachining process, PolyMUMPS. The actuation system is designed to provide motion to biological microelectromechanical systems (BioMEMS) in aqueous environments. This paper presents the design and experimental demonstration of the actuation system. The in-depth analysis of the thermal, mechanical, and fabrication aspects of the actuation system are outlined, and the experimental procedure and test parameters are discussed.Copyright © 2011 by ASME

Carbon nanotubes can be grown vertically from a substrate to form dense forests hundreds of microns tall. The space between the nanotubes can then be filled with carbon using chemical vapor deposition to create solid structures. These infiltrated structures can be detached from the substrate and operated as single-piece MEMS. To facilitate the design of compliant microdevices using this process, we explored the influence of two fabrication parameters—iron layer thickness and infiltration time—on the material’s mechanical properties, using the fracture strain to judge suitability for compliance. We prepared samples of a simple meso-scale cantilever beam pattern at various levels of these parameters, applied vertical loads to the tips of the beams, and recorded the forces and deflections at brittle failure. These data were then used in conjunction with a nonlinear FEA model of the beams to determine Young’s modulus and fracture stress for each experimental setting. From these data the fracture strains were obtained. The highest fracture strain observed was 2.48%, which is approximately 3.5 times that of polycrystalline silicon. This was obtained using an iron layer thickness of 10 nm and an infiltration time of 30 minutes. We used a test device—a compliant gripper mechanism for holding mammalian egg cells—to demonstrate the use of this material in compliant MEMS design.Copyright © 2011 by ASME

This paper outlines the adaptation of a mathematical computer model used to simulate the motion of DNA particles in order to determine the best geometry and setup for a prototype cell injection system. The model predicts DNA motion due to electrophoresis near micromachined electrodes. Ten key electrode parameters are identified to test for significance, and three key test measurements are identified to help compare the various setups. A simple design of experiment is used to organize and analyze the data collected from forty-one simulations of the DNA motion within the electric field. Based on the simulations of attracting DNA to the lance for injection, it is found that a compact ring electrode placed underneath an insulated lance will yield the optimal results. Two additional areas for research are recommended.Copyright © 2011 by ASME

This paper demonstrates a low stiffness compliant joint design obtained by balancing the energy stored within individual components of the mechanism. As a step toward a fully-compliant zero-stiffness joint, this paper presents the design of a partially-compliant joint. A wireform torsion bar partially compliant joint was optimized using a pseudo rigid body model. A low stiffness design was obtained by balancing the energy stored within individual components of the mechanism. The joint was then fabricated using piano wire, polypropylene and Delrin®. During testing it was found that friction in the joint was greater than any internal forces allowing the joint to be neutrally stable in all positions. Dynamic force deflection data on the joints was collected in order to investigate the friction characteristics. The Delrin® joint exhibited only Coulomb friction while the polypropylene model exhibited both Coulomb and viscous friction.Copyright © 2011 by ASME

Nanoinjection is an innovative approach for the electromechanical injection of DNA into cells, in which DNA is electrically attracted to a lance, inserted into a cell, and repelled by reversing the electrical polarity. In previous work, the lance has been micromachined as part of an on-chip microelectromechanical system. This work investigates a Stand-Alone Lance concept, where the lance and other components are independent of a common substrate. The Stand-Alone Lance may make nanoinjection more accessible to researchers and be more compatible with lab equipment commonly available in transgenic facilities. Required parameters for the electrode are investigated using a mathematical computer model. Different materials and fabrication processes for the metal lance are also considered. Additional testing was performed using tungsten probes, including mock injections on mouse egg cells. Based upon the optimistic cell viability rate, it is recommended to further investigate the use of the Stand-Alone Lance to perform nanoinjections.Copyright © 2011 by ASME

This paper explored the deflection and buckling of fixed-guided beams. It uses an analytical model for predicting the reaction forces, moments, and buckling modes of a fixed-guided beam undergoing large deflections. One of the strengths of the model is its ability to accurately predict buckling behavior and the buckled beam shape. The model for the bending behavior of the beam is found using elliptic integrals. A model for the axial deflection of the buckling beam is also developed based on the equations for stress and strain and the buckling profile of the beam calculated with the elliptic integral solution. These two models are combined to predict the performance of a beam undergoing large deflections including higher order buckling modes. The force vs. displacement predictions of the model are compared to the experimental force vs. deflection data of a bistable mechanism and a thermomechanical in-plane microactuator (TIM). The combined models show good agreement with the force vs. deflection data for each device. The paper’s main contributions include the addition of the axial buckling model to existing beam bending models, the exploration of the deflection domain of a fixed-guided beam, and the demonstration that nonlinear finite element models may incorrectly predict a beam’s buckling mode unless unrealistic constraints are placed on the beam.Copyright © 2010 by ASME

This paper describes the protocol and presents the results for DNA motion experiments using fabricated macroscale gel electrophoresis devices. Gel electrophoresis is a process used to separate/move DNA, RNA or protein molecules using an electric field through a gel matrix (electrolytic solution). In electrolytic solutions, the current conduction is due to a transport of ions (anions and cations). A better understanding of electrophoretic fundamentals allows for modeling the motion of DNA during electrophoresis. The model is validated through comparison with the experimental results. The model and experimental validation will be used to improve the process of cellular nanoinjection of DNA, currently in development in our lab.Copyright © 2010 by ASME

We are developing a new technique, called nanoinjection, to insert foreign DNA into a living cell. Such DNA transfection is commonly used to create transgenic organisms vital to the study of genetics, immunology, and many other biological sciences. In nanoinjection, DNA, which has a net negative charge, is electrostatically attracted to a micromachined lance. The lance then pierces the cell membranes, and the voltage on the lance is reversed, repelling the DNA into the cell. This paper presents a mathematical model to predict the motion (trajectory) of DNA particles within a cell in the presence of the electric field developed by the lance and the substrate. The model is used to predict the scattering of DNA through the cell due to electrostatic repulsion. We are currently preparing experiments which will be used to validate the model.Copyright © 2009 by ASME

The ultimate goal of this work is to develop an automated MEMS-based lab-on-a-chip microinjector. This paper outlines one phase of that work: testing the feasibility of a pumpless, polysilicon MEMS microneedle for use in the proposed MEMS-based lab-on-a-chip microinjector. The pumpless MEMS microneedle operates on the principle of attraction and repulsion of DNA using electrostatic charges. Prototype microneedles were fabricated using a multi-layer surface micromachining process. DNA stained with a fluorescent dye (4‘, 6-DIAMIDINO-2-PHENYLINDOLE DIHYDROCHLORIDE or DAPI) was visualized using fluorescent illumination as the DNA was attracted to and repelled from the tips of MEMS microneedles using a 1.5 V DC source. The pumpless MEMS microneedle represents an important and significant step in the development of a self-contained, automated, MEMS-based microinjection system.Copyright © 2008 by ASME

Microelectromecahanical system (MEMS) actuation is a growing area of research. One obstacle for use of actuation in MEMS applications is the difficulty of proper sensing. Recent work has been done that shows the potential for thermomechanical in-plane microactuators (TIMs) to act as self-sensors by using the piezoresistive characteristic of silicon. However, in order to implement this technology a calibration method needs to be devised to account for variations between TIMs. This work presents an approach for this calibration consisting of two parts that compensate for variation in fabrication and material properties. Test structures are presented that will enable this calibration to be done on-chip, and validation is given for the usability of this approach. Two validation approaches are used. For the first approach, data previously gathered was analyzed using the TIM itself for calibration. This approach showed significant correlation with the model; however, this approach confounds any sensing signal and therefore was used only for general model validation. The second approach uses a novel calibration structure that decouples the mechanical and electrical characteristics. This approach showed correlation with test data within the bounds of experimental uncertainty in nearly all cases. Suggestions are given concerning implementation.Copyright © 2008 by ASME

This paper presents the design of a damped ortho-planar spring that uses viscoelastic constrained-layer damping to reduce the free response oscillations of the spring and suppress modal resonances in that response. Background, theory, and applications surrounding fully-compliant ortho-planar springs and viscoelastic damping treatments are first discussed. Next, the effect of various constrained layer thickness on the spring constant, damping ratio, equivalent viscous damping ratio, modal frequencies, and modal damping ratios are compared, and trends discussed. The results show that the equivalent viscous damping co-efficient of the viscoelastically-damped spring can be increased to nearly 2.5 times that of the reference configuration without significantly changing the size of the constraining layer or the spring constant of the ortho-planar spring. Viscoelastically-damped ortho-planar springs are also shown to successfully remove mechanical noise from a contact resistance test stand.Copyright © 2008 by ASME

This paper describes the design of a novel multi-stable compliant mechanism capable of large angle deflections. The multi-stable COmpliant Rolling-contact Element (CORE), reduces friction, allows for large angular displacements, and requires no external force to remain in its multiple equilibrium positions. This paper develops and discusses seven methods to create multi-stable mechanisms from the CORE. These seven methods have different characteristics and advantages.Copyright © 2007 by ASME

Recent interest in small Unmanned Air Vehicles (UAVs) has led to advances in wing technologies. Deployable wings reduce required storage space while providing greater range during flight. This paper presents a compliant rotating joint which is bistable and features a locking characteristic that prevents the wing from reverting back to the undeployed configuration during flight. The two stable positions occur at local strain energy minima about 90 degrees apart, but can be adjusted by the designer. A pseudo rigid body model is illustrated for the joint, based on a four-bar linkage. Such a joint mechanism can be designed for any wing, by using the pseudo rigid body model to optimize link lengths and position the instant center appropriately. In addition, the mechanism can be cut out within a single plane for ease of manufacture and assembly.

A number of designs for microneedles have recently been developed to facilitate the painless injection of medications, such as insulin, into the human body [1–6]. The injections are painless because the needles penetrate the skin predominantly in the epidermal layer of skin which contains no nerve endings. Some microneedles do not contain inner channels and are simply coated with medication, the intent being that the transdermal drug delivery will take place through absorption over time. A more effective method of medicinal transfer is to equip the microneedles with an inner channel to facilitate rapid delivery of the medication to the skin.Copyright © 2007 by ASME

This paper presents the robust design optimization of an RF-MEMS direct contact cantilever switch for minimum actuation voltage and opening time, and maximum power handling capability. The design variables are the length and thickness of the entire cantilever, the widths of the sections of the cantilever, and the dimple size. The actuation voltage is obtained using a 3-D structural-electrostatic finite-element method (FEM) model, and the opening time is obtained using the same FEM model and the experimental model of adhesion at the contact surfaces developed in our previous work. The model accounts for an unpredictable variance in the contact resistance resulting from the micromachining process for the estimation of the power handling. This is achieved by taking the ratio of the root mean square power of the RF current (ldquosignalrdquo) passing through the switch to the contact temperature (ldquonoiserdquo) resulting from the possible range of the contact resistance. The resulting robust optimization problem is solved using a Strength Pareto Evolutionary Algorithm, to obtain design alternatives exhibiting different tradeoffs among the three objectives. The results show that there exists substantial room for improved designs of RF-MEMS direct-contact switches. It also provides a better understanding of the key factors contributing to the performances of RF-MEMS switches. Most importantly, it provides guidance for further improvements of RF-MEMS switches that exploit complex multiphysics phenomena.

Previous models and measurements of MEMs adhesion have focused on steady-state adhesion behavior. This approach is inadequate for micromachined switches (such as RF MEMS switches) because it gives no information about the time required for contact opening, an important specification. We propose a technique to measure the switch opening time and present substantial experimental data for switches with gold-gold contacts. The data demonstrate that contact opening time increases dramatically as contact dimple area increases or as pull-apart force or contact resistance decrease. A model of opening time is also presented with model parameters that fit the experimental data.

Improving the power handling capability of direct contact RF MEMS switches requires a knowledge of conditions at the contact. This paper models the temperature rise in a direct contact RF MEMS switch, including the effects of electrical and thermal contact resistance. The maximum temperature in the beam is found to depend strongly on the power dissipation at the contact, with almost no contribution from dissipation due to currents in the rest of the switch. Moreover, the maximum temperature is found to exceed the limit for metal softening for a significant range of values of thermal and electrical contact resistance. Since local contact asperity temperature can be hundreds of degrees higher than the bulk material temperature modeled here, these results underscore the importance of understanding and controlling thermal and electrical contact resistance in the switch.