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This paper presents the development of an origami-inspired support system (the OriGuide) that enables the insertion of flexible instruments using medical robots. Varying parameters of a triangulated cylindrical origami pattern were combined to create an effective highly compressible anti-buckling system that maintains a constant inner diameter for supporting an instrument and a constant outer diameter throughout actuation. The proposed origami pattern is composed of two repeated patterns: a bistable pattern to create support points to mitigate flexible shaft buckling and a monostable pattern to enable axial extension and compression of the support system. The origami-based portion of the device is combined with two rigid mounts for interfacing with the medical robot. The origami-based portion of the device is fabricated from a single sheet of polyethylene terephthalate. The length, outer diameter, and inner diameter that emerge from the fold pattern can be customized to accommodate various robot designs and flexible instrument geometries without increasing the part count. The support system also adds protection to the instrument from external contamination.

The cylindrical cross-axis flexural pivot (CCAFP) is proposed as an ultra-compact flexure capable of being integrated into hollow cylindrical shafts, enabling shaft motion without inhibiting cables or other components inside the shaft. Mechanism geometry, materials, and manufacturing are proposed and the results analyzed and tested. A parametric finite element model of the CCAFP was created to analyze the force-deflection and strain-deflection relationships and the predicted behavior was verified by experiment. Analytic models of stress-limiting cam-surfaces suggest even larger motions may be possible when not limited by current practical constraints. The CCAFP is demonstrated and tested at multiple size scales and in multiple materials, ranging from 28.6 mm diameter 4130 steel (achieving 9 degrees of angular deflection) to 3 mm diameter NiTi (achieving an angular deflection of 85 degrees). The results are generalized to apply to a range of applications, and the CCAFP particularly shows promise for implementation in minimally invasive surgical instruments to decrease instrument size while maintaining instrument performance.

This paper reports on the design, fabrication, and testing of a fully-compliant mechanism designed for precise parallel guidance. The mechanism is designed to guide arrays of micro-scale needles for straight-line injections of thousands of culture cells simultaneously. During injection, the needle array is to be lowered into the cell culture dish. It must be guided carefully during insertion of the needles into the cells because any rotation or transverse motion of the needles during insertion can lead to tearing of the delicate cell membranes, leading to cell death. The injection system consists of a fully-compliant mechanism designed for straight-line motion, while resisting motions in other direction. Successive prototypes are shown to illustrate the process of design, and to illustrate the benefits of the final system. Prototypes were demonstrated using deep reactive ion etching of silicon wafers, as well as rapid prototyping using a three-dimensional printer in ABS polymer. The final system consists of a single, 3-D-printed part that incorporates compliance to guide the needle array over a distance of about 1.5 mm while restraining transverse deflections or rotations. Testing shows that injections performed using the system result in high cell viability, suggesting that the system appropriately restrains off-axis motions. While the system demonstrated here is designed specifically for biological research, it may be adapted to manufacturing, position control, or any other application requiring straight-line motion while minimizing transverse deflections or rotations.

This paper investigates the design of a nano-injection system that can deliver genetic material to cells within live tissue. The approach to creating such a system was to create candidate designs that meet all the requirements for successful in vivo injection and can be fabricated using silicon etching. The designs were tested through large-scale prototyping and through models that describe the systems’ behavior on the micrometer scale. One design consists of an array of lances on a rigid backing. The other design consists of an array of lances grouped in sets of three on a backing that can conform to the shape of the tissue being injected. Each design was prototyped in 3D printed ABS plastic. Preliminary results were qualitative and showed that the rigid and flexible designs performed similarly on mostly flat and irregular surfaces. On convex surfaces with a strong curvature (radius of curvature of about 2 cm), the flexible array gave slightly better results. Final testing gave a quantitative comparison of the two designs’ efficiencies on strongly curved convex surfaces. These results supported the preliminary results that the flexible array is more efficient in reaching points on the tissue than the rigid array is. As the applied force increased, each array performed more efficiently.Copyright © 2016 by ASME

This paper presents a performance-based comparison of quadratic shell elements with shear deformation and 3-D quadratic solid elements for modeling geometrically non-linear coupled in-plane and out-of-plane deflection of thin-film compliant microelectromechanical systems. A mesh density study of a single out-of-plane torsional compliant element indicates that a relatively coarse shell element mesh can produce force, displacement, and stress results very similar to those predicted by a much larger and computationally costly 3-D solid element model for out-of-plane loading. Shell and 3-D solid element models of a macro-scale prototype of a MEMS compliant lamina emergent constant-force mechanism are shown to agree very well with experientially acquired force displacement data, and to agree well in their estimates of Von Mises stresses. Close agreement of shell element and 3-D solid element models is also demonstrated for models of a thin-film MEMS constant-force mechanism and a thin-film MEMS cellular lance mechanism. Both of these mechanisms exhibit highly non-linear mechanism stiffness, and large, coupled in and out-of-plane displacements. Together, these results strongly suggest that quadratic shell elements with shear deformation can be used to model the coupled in-plane and out-of-plane motion of thin-film compliant mechanisms.

This paper introduces piezoresistive encoders that can provide information on the performance of ratcheting actuation systems, and may be useful in future applications that require position determination. One unique feature of the encoders is that they gain their piezoresistance from the bulk properties of polycrystalline silicon without additional fabrication steps. In this study, two encoders are considered: a parallel-guiding encoder in an on-chip Wheatstone bridge, and a piezoresistive microdisplacement transducer (PMT) encoder in an on-chip Wheatstone bridge. In tests, the encoders each generated measurable signals, with the PMT encoder providing the best sensitivity. The PMT encoder operated at actuation frequencies up to 920 Hz and produced a signal between 2 V and 3.2 V (applied gain of 1000). The PMT encoder produced unique signals corresponding to distinct ideal and non-ideal behaviors of a ratchet wheel actuation system.

This paper presents a microelectromechanical test device and calibration method for finding torsional piezoresistive coefficients for micro sensing applications. The test device consists of a slider-crank connected to two torsional legs. The slider-crank creates torsional stress in the legs which causes a change in the electrical resistance through the legs. A model that predicts the effects of a scissor hinge on the slider-crank is presented. Torsional stresses in the legs are calculated and the legs are discretized into long parallel resistors and the stresses applied to each resistor. Assuming a second-order piezoresistance, an optimization is then done to find the piezoresistive coefficients by changing them until the model prediction fits the test data. These coefficients can be used to predict angular displacement from resistance measurements in fully integrated torsional sensors.

This paper describes a battery-free threshold shock sensor with wireless readout via RFID circuitry. The entire package is designed to provide low-cost sensors for monitoring shock loads in applications such as shipping. The sensor is based on a mechanical bistable mechanism laser-cut from a single Delrin layer which switches states when exposed to accelerations above a threshold. The sensor was tested using quasi-static accelerations in a centrifuge, pulsed accelerations from an impact event, and vibration (sinusoidal) accelerations on a shaker table. Measured threshold accelerations were similar in magnitude for the three load types, although they varied slightly due to dynamic effects. This phenomenon was further explored using a dynamic model of the sensor. Threshold accelerations in the range of 30-50 G's were measured, and these values can be varied by changing the mass of the accelerometer's outer frame. Wireless readout was successfully demonstrated by using the mechanical accelerometer as an electrical switch connected to the sensor input of an RFID chip.

Compliant piezoresistive MEMS sensors exhibit great promise for improved on-chip sensing. As compliant sensors may experience complex loads, their design and implementation require a greater understanding of the piezoresistive effect of polysilicon in bending and combined loads. This paper presents experimental results showing the piezoresistive effect for these complex loads. Several n-type polysilicon test structures, fabricated in MUMPs and SUMMiT processes, were tested. Results show that, while tensile stresses cause a linear decrease in resistance, bending stresses induce a nonlinear rise in resistance, contrary to the effect predicted by linear models. In addition, tensile, compresive, and bending loads combine in their effects on resistance. The experimental data illustrates the inability of linear piezoresistance models to predict the piezoresistive trends of polysilicon in bending and combined loads, indicating the need for more complete nonlinear models appropriate for these loading conditions.

This paper presents the design, fabrication, and testing of a miniature latching accelerometer that does not require electrical power. Latching is attained by using a bistable compliant mechanism that switches from one mechanical position to another when the force on the accelerometer exceeds a threshold value. Accelerometers were fabricated by laser cutting the compliant mechanism switch out of both ABS and Delrin plastic sheets. Packaging consisted of gluing the single compliant layer to a supporting substrate. The switching thresholds of the accelerometers were varied from 10g to 800g by varying the surface area of the free moving section between 100 and 500 mm2.

A new, compact 2 degree-of-freedom mechanism 4.1 mm in diameter suitable for robotically controlled surgical operations is presented. Current commercially available robotically controlled instruments achieve high dexterity defined by three degrees of freedom and relatively confined swept volume at just under 1 cm in diameter. Current smaller diameter instruments result in high part count and large swept volumes (less dexterity). A meso-scale rolling contact gripping mechanism is proposed as an alternative. The manufacturing of the parts is made feasible by Metal Laser Sintering, which can produce parts that are difficult to replicate with traditional manufacturing methods. The resulting instrument has only 6 parts and a small swept volume. Instrument actuation and control by a surgical robotic system is demonstrated.Copyright © 2015 by ASME

Air-suspension of transmission-line structures using microelectromechanical systems (MEMS) technology provides the effective means to suppress substrate losses for radio-frequency (RF) signals. However, heating of these lines augmented by skin effects can be a major concern for RF MEMS reliability. To understand this phenomenon, a thermal energy transport model is developed in a simple analytical form. The model accounts for skin effects that cause Joule heating to be localized near the surface of the RF transmission line. Here, the model is validated through experimental data by measuring the temperature rise in an air-suspended MEMS coplanar waveguide (CPW). For this measurement, a new experimental methodology is also developed allowing direct current (dc) electrical resistance thermometry to be adopted in an RF setup. The modeling and experimental work presented in this paper allow us to provide design rules for preventing thermal and structural failures unique to the RF operation of suspended MEMS transmission-line components. For example, increasing the thickness from 1 to 3 mum for a typical transmission line design enhances power handling from 5 to 125 W at 20 GHz, 3.3 to 80 W at 50 GHz, and 2.3 to 56 W at 100 GHz (a 25-fold increase in RF power handling)

We propose an extended finite element-boundary integral method (EFE-BI) to model the electromagnetic (EM) behavior of RF-MEMS switches over a wide frequency range from UHF to terahertz. Our new method integrates EM with finite element heat transfer analysis to extract heat dissipation on the micrometer-scale switch beam due to the non-uniform radio frequency (RF) current distribution. The developed EFE-BI technique is an extension of the standard finite element-boundary integral (FE-BI) method to allow for accurate characterization of RF-MEMS structures whose entire size is a small fraction of a wavelength (λ/250 or less) and may contain dimensions in the order of λ/50 000 or less. Our model predictions exhibit good agreement with experimental results obtained independent of the current study.

Bistable mechanical devices remain stable in two distinct positions without power input. They find application in valves, switches, closures, and clasps. Mechanically bistable behavior results from the storage and release of energy, typically in springs, with stable positions occurring at local minima of stored energy. Compliant mechanisms offer an elegant way to achieve this behavior by incorporating both motion and energy storage into the same flexible element. Interest in compliant bistable mechanisms has also recently increased because of the advantages of bistable behavior in many micro-electro-mechanical systems (MEMS). Design of compliant or rigid-body bistable mechanisms typically requires simultaneous consideration of both energy storage and motion requirements. This paper simplifies this process by developing theory that provides prior knowledge of mechanism configurations that guarantee bistable behavior. Configurations which include one or more translational, or slider, joints are studied in this work. Several different mechanism types are analyzed to determine compliant segment placement that will ensure bistable mechanism operation. Examples demonstrate the power of the theory in design.

Bistable mechanisms, which have two stable equilibria within their range of motion, are important parts of a wide variety of systems, such as closures, valves, switches, and clasps. Compliant bistable mechanisms present design challenges because the mechanism’s energy storage and motion characteristics are strongly coupled and must be considered simultaneously. This paper studies compliant bistable mechanisms which may be modeled as four-link mechanisms with a torsional spring at one joint. Theory is developed to predict compliant and rigid-body mechanism configurations which guarantee bistable behavior. With this knowledge, designers can largely uncouple the motion and energy storage requirements of a bistable mechanism design problem. Examples demonstrate the power of the theory in bistable mechanism design.

Electrostatic comb drives are widely used in microelectromechanical devices. These comb drives often employ rectangular fingers which produce a stable, constant force output as they engage. This paper explores the use of shapes other than the common rectangular fingers. Such shaped comb fingers allow customized force-displacement response for a variety of applications. In order to simplify analysis and design of shaped fingers, a simple model is developed to predict the force generated by shaped comb fingers. This model is tested using numerical simulation on several different sample shaped comb designs. Finally, the model is further tested, and the use of shaped comb fingers is demonstrated, through the design, fabrication, and testing of tunable resonators which allow both up and down shifts of the resonant frequency. The simulation and testing results demonstrate the usefulness and accuracy of the simple model. Finally, other applications for shaped comb fingers are described, including tunable sensors, low-voltage actuators, multistable actuators, or actuators with linear voltage-displacement behavior.

A bistable mechanism has two stable states within its range of motion. Its advantages include the ability to stay in two positions without power input and despite small external disturbances. Therefore, bistable micro-mechanisms could allow the creation of MEMS with improved energy efficiency and positioning accuracy. This paper presents bistable micro-mechanisms which function within the plane of fabrication. These bistable mechanisms, called “Young” bistable mechanisms, obtain their energy storage characteristics from the deflection of two compliant members. They have two pin joints connected to the substrate, and can be constructed of two layers of polysilicon. The pseudo-rigid-body model is used to analyze and design these mechanisms. This approach allows greater freedom and flexibility in the design process. The mechanisms were fabricated and tested to demonstrate their bistable behavior and to determine the repeatability of their stable positions.

The pseudo-rigid-body model concept allows compliant mechanisms to be analyzed using well-known rigid-body kinematics. This paper presents a pseudo-rigid-body model for initially curved pinned-pinned segments that undergo large, nonlinear deflections. The model approximates the segment as three rigid members joined by pin joints. Torsional springs placed at the joints model the segment’s stiffness. This model has been validated by fabricating several such segments from a variety of different materials. Testing of the force-deflection behavior of these segments verified the accuracy of the model.

Polycrystalline silicon (polysilicon) is a material commonly used for micro-electro-mechanical systems (MEMS) for which reliable mechanical properties data is not available, especially for devices that have dimensions on the order of microns. This paper proposes a method for using test data that accounts for the uncertainties in mechanical properties and presents data from tests of polysilicon that may be used in the future design of polysilicon MEMS. The testing of 161 micro-devices to failure, results in a recommendation for design that the nominal strain be maintained below 0.0055. 1998 Elsevier Science Ltd. All rights reserved.

Connecting technology to biologic discovery is a core focus of non-viral gene therapy biotechnologies. One approach that leverages both the physical and electrical function of microelectromechanical systems (MEMS) in cellular engineering is a technology previously described as lance array nanoinjection (LAN). In brief, LAN consists of a silicon chip measuring 2 cm by 2 cm that has been etched to contain an array of 10 μm tall, solid lances that are spaced every 10 μm in a grid pattern. This array of lances is used to physically penetrate hundreds of thousands of cells simultaneously and to then electrically deliver molecular loads into cells. In this present work, two variables related to the microfabrication of the silicon lances, namely lance geometry and coating, are investigated. The purpose of both experimental variables is to assess these parameters' effect on propidium iodide (PI), a cell membrane impermeable dye, uptake to injected HeLa 229 cells. For the lance geometry experimentation, three different microfabricated lance geometries were used which include a flat/narrow (FN, 1 μm diameter), flat/wide (FW, 2–2.5 μm diameter), and pointed (P, 1 μm diameter) lance geometries. From these tests, it was shown that the FN lances had a slightly better cell viability rate of 91.73% and that the P lances had the best PI uptake rate of 75.08%. For the lance coating experimentation, two different lances were fabricated, both silicon etched lances with some being carbon coated (CC) in a

RF MEMS switches have demonstrated excellent performance. However, before such switches can be fully implemented, they must demonstrate high reliability and robust power-handling capability. Numerical simulation is a vital part of design to meet these goals. This paper demonstrates a fully integrated electrothermal model of an RF MEMS switch which solves for RF current and switch temperature. The results show that the beam temperature increases with either higher input power or increased frequency. The simulation data are used to predict switch failure due to temperature-related creep and self pull-in over a wide range of operating frequency (0.1-40 GHz) and power input (0-10 W). Self pull-in is found to be the dominant failure mechanism for an example geometry.

This paper introduces a metamorphic erectable cell restraint (MECR) to provide cell restraint in genetic research. A micro-electromechanical systems (MEMS) metamorphic mechanism with two phases of motion was designed to grasp individual embryos about their midplane. The first phase of motion lifts a compliant gripper approximately 40 μm (about half the diameter of an embryo). The gripper then closes in the second phase to grasp the embryo. The metamorphic mechanism includes compliant mechanism components which are analyzed here. A microscale prototype was fabricated from polysilicon and used to demonstrate the mechanism’s two phase motion.Copyright © 2012 by ASME

A nanoinjection lance array has been developed to inject foreign genetic material into thousands of cells at once using electrophoresis to attract and repel particles to and from the lances. A unique combination of isotropic and anisotropic etch processes are used to fabricate the four million 1 μm by 8 μm solid lances on a 2 cm by 2 cm chip. Initial studies show high cell viability when the lance array is used to pierce through a culture of HeLa cancer cells, often used for genetic research. A mathematical computer model simulating motion of attracted or repelled particles informs the design of the nanoinjection lance array system. The nanoinjection lance array provides an efficient, convenient, and quick way to simultaneously inject thousands of cells for a wide range of genetic research applications.Copyright © 2012 by ASME

Static balancing is an important contribution to compliant mechanisms enabling low operating force, thus allowing high mechanical efficiency. Preloading is generally needed in statically balanced compliant mechanisms, which at smaller scales presents a significant challenge. Physical handling of zero-force structures without causing damage also becomes difficult. This paper presents a solution to both of these issues. A novel compliant connection mechanism based on bistable beams was used to precisely preload the system in the direction of motion without backlash. Once this bistable mechanism is engaged by loading beyond its threshold, the system is in operating condition, i.e. the ON position. When the connection mechanism is disengaged (OFF position), it is much stiffer than it is in the statically balanced state and therefore more robust for handling purposes. As a demonstrator, we present the first statically balanced gripper with a fully compliant ON/OFF-connection mechanism allowing pre-loading collinear with the direction of motion. The combination of a pre-loaded bistable mechanism (i.e. negative stiffness) and a voluntary closing gripper (i.e. positive stiffness) is used for static balancing (i.e. zero stiffness and zero actuation force). The results show that the actuation force is reduced by at least 91% when the preload is engaged. The proposed ON/OFF connection shows a promising method for pre-loading compliant mechanisms or related devices.Copyright © 2012 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

We present a new technique for fabricating compliant mechanisms from stamped metal sheets. The concept works by providing thinned segments to allow rotation of flexural beams 90 deg about their long axis, effectively providing a flexure as wide as the sheet’s thickness. The method is demonstrated with the design and fabrication of a metal bistable mechanism for use as a threshold accelerometer. A new model based on elliptic integral solutions is presented for bistable mechanisms incorporating long, thin flexures. The resulting metal bistable mechanisms are tested for acceleration threshold sensing using a drop test and a vibration test. The mechanisms demonstrate very little variation due to stress relaxation or temperature effects. The force-displacement behavior of a mechanism is also measured. The mechanisms’ switching force is less than the designed value because of out-of-plane motion and dynamic effects.

This paper presents an alternative to fabrication methods commonly used in compliant mechanisms research, resulting in a new class of compliant mechanisms called wireform mechanisms. This technique integrates torsional springs made of formed wire into compliant mechanisms. In this way the desired force, stiffness, and motion can be achieved from a single piece of formed wire. Two techniques of integrating torsion springs are fabricated and modeled: helical coil torsion springs and torsion bars. Because the mechanisms are more complex than ordinary springs, simplified models, which aid in design, are presented, which represent the wireform mechanisms as rigid-body mechanisms using the pseudo-rigid-body model. The method is demonstrated through the design of a mechanically tristable mechanism. The validity of the simplified models is discussed by comparison to finite element models and, in the case of the torsion-bar mechanism, to experimental measurements.

This paper presents the design, manufacture, and testing of a battery-free, wireless threshold accelerometer based on a fully compliant bistable mechanism (FCBM). The FCBM stores threshold acceleration measurements mechanically, eliminating the need for electrical power. The sensorpsilas state can be read wirelessly via a passive RFID tag. Because information can be stored in these tags for over 25 years, the sensor can be left unattended for long periods of time. The FCBM portion of the sensor is laser cut from a single sheet of plastic (Delrin) and integrated with an Atmel ATA5570 RFID chip. Both elements can be manufactured at low cost. The G-force needed to exceed the shock threshold can be varied by changing the mass of the FCBM. Multiple sensors were tested using three different methods. The first method was a centrifuge, providing a constant force input. The second method was a drop test that gave an impulse input to the sensor. The final method used a shaker table to provide a sinusoidal input. In each of these tests, it was found that the FCBM sensed the correct acceleration and retained its mechanical state. A number of prototype sensors were constructed with different masses resulting in threshold accelerations between 15 and 180 Gpsilas. The overall size of these sensors was approximately 28 mm x 26 mm. The RFID tags operate at 150 kHz and were read using a commercial off-the-shelf reader with a range of approximately 3 cm. Longer range readers are readily available at higher operating frequencies.

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, fabrication, and testing of a force sensor for integrated use with thermomechanical in-plane microactuators. The force sensor is designed to be integrated with the actuator and fabricated in the same batch fabrication process. This sensor uses the piezoresistive property of silicon as a sensing signal by directing the actuation force through two thin legs, producing a tensile stress. This tensile load produces a resistance change in the thin legs by the piezoresistive effect. The resistance change is linearly correlated with the applied force. The device presented was designed by considering both its piezoresistive sensitivity and out-of- plane torsional stability. A design trade-off exists between these two objectives in that longer legs are more sensitive yet less stable. Fabrication of the sensor design was done using the MUMPs process. This paper presents experimental results from this device and a basic model for comparison with previously attained piezoresistive data. The results validate the concept of integral sensing using the piezoresistive property of silicon.

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.

For many applications, radio frequency microelectromechanical systems (RF MEMS) switches require very fast switching times so that they are capable of switching thousands of times each second. Contact adhesion tends to slow switches by increasing the time required to break the contact and open the switch. Previous work showed that typical switches have a contact opening time exceeding 1 ms, which is far too slow for many applications. This paper presents a dynamic, transient model to predict the time required to break the contact. The model considers both the motion of the switch body and the adhesion at the contact. The model has been validated by comparing it to experimental data. The model shows that vibrations in the switch body can be instrumental in dramatically reducing contact opening time by a factor of nearly 1000, leading to acceptable switch speeds.Copyright © 2006 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.

Despite the excellent characteristics of RF MEMS switches, they generally suffer from low power-handling capability. This limitation is due to the complex interactions among electromagnetic losses, heat transfer, and mechanical deformations associated with the switches. To understand these failure mechanisms, we proposed a multiphysics model (Jensen, B.D. et al., IEEE Microwave and Wireless Components Letters, vol.13, no.9, p.364-66, 2003). This model is based on an extended finite element-boundary integral (EFE-BI) model that allows efficient modeling of the boundary (MEMS beam for our case) exterior to the volumetric region modeled by the standard FE-BI method. The condition number of the resulting EFE-BI matrix system increases rapidly as the frequency decreases. The matrix condition number required at 2 GHz warrants computational accuracy beyond the capability of normal CPUs. For this reason, our EFE-BI analysis and validation of the code were limited to high frequency cases. We propose a preconditioning approach that lowers the condition number of the system. The proposed approach allows for fast, efficient analysis of RF MEMS switches at practical RF frequencies as low as 500 MHz, which will enable the desired multiphysics modeling.

In many MEMS applications, it is desirable to amplify the force or displacement of an actuator or transducer. Devices that amplify force or mechanical advantage typically achieve this at the expense of displacement or geometric advantage. Likewise, devices that amplify geometric advantage do so at the expense of mechanical advantage. This paper proposes a device topology based on a four-link mechanism with compliant segments in place of hinges. Finite-element analysis and optimization were used to develop a Pareto set of solutions quantifying the force / displacement trade-off for a variety of loading conditions. Depending on these conditions, this device is capable of multiplying force inputs by as much as 23.7 and displacement inputs by as much as 588. Efficiency of these designs improves as the two objectives (mechanical and geometric advantage) are considered jointly in a multicriteria optimization problem rather than individually.

Although many actuators employing electrostatic comb drives have been demonstrated in a laboratory environment, widespread acceptance in mass produced microelectromechanical systems (MEMS) may be limited due to issues associated with low drive force, large real estate demands, high operating voltages, and reliability concerns due to stiction. On the other hand, comb drives require very low drive currents, offer predictable response, and are highly compatible with the fabrication technology. The expand the application space and facilitate the widespread deployment of self-actuated MEMS, a new class of advanced actuation systems has been developed that maintains the highly desirable aspects of existing components, while significantly diminishing the issues that could impede large scale acceptance. In this paper, the authors will present low-voltage electrostatic actuators that offer a dramatic increase in force over conventional comb drive designs. In addition, these actuators consume only a small fraction of the chip area previously used, yielding significant gains in power density. To increase the stroke length of these novel electrostatic actuators, the authors have developed highly efficient compliant stroke amplifiers. The coupling of compact, high-force actuators with fully compliant displacement multipliers sets a new paradigm for highly integrated microelectromechanical systems.

We have designed, fabricated, tested and modeled a first generation small area test structure for MEMS fracture studies by electrostatic rather than mechanical probing. Because of its small area, this device has potential applications as a lot monitor of strength of fatigue of the MEMS structural material. By matching deflection versus applied voltage data to a 3D model of the test structure, we develop high confidence that the local stresses achieved in the gage section are greater than 1 GPa. Brittle failure of the polycrystalline silicon was observed.

A bistable mechanism has two stable states within its range of motion. Its advantages include the ability to stay in two positions without power input and despite small external disturbances. Therefore, bistable micro-mechanisms could allow the creation of MEMS with improved energy efficiency and positioning accuracy. This paper presents the first bistable MEMS which function within the plane of fabrication. These bistable mechanisms, known as “Young” bistable mechanisms, obtain their energy storage characteristics from the deflection of two compliant members, have two pin joints connected to the substrate, and can be constructed of two layers of polysilicon. The pseudo-rigid-body model overcomes problems with nonlinearities in the analysis and design of these mechanisms. This approach allows greater freedom and flexibility in the design process. Testing of the mechanisms demonstrated their bistable behavior and the repeatability of the stable positions.

This paper reports the effects of various parameters on the attraction and repulsion of DNA to and from a silicon lance. An understanding of DNA motion is crucial for a new approach to insert DNA, or other foreign microscopic matter, into a living cell. The approach, called nanoinjection, uses electrical forces to attract and repel the desired substance to a micromachined lance designed to pierce the cell membranes. We have developed mathematical models to predict the trajectory of DNA. The mathematical model allows investigation of the attraction/repulsion process by varying specific parameters. We find that the ground electrode placement, lance orientation and lance penetration significantly affect attraction or repulsion efficiency, while the gap, lance direction, lance tip width, lance tip half-angle and lance tip height do not.

Fully compliant bistable micromechanisms (FCBMs) have potential use in numerous applications, including switches, relays, shutters and low-power sensing arrays. Two-dimensional finite element models for these FCBMs have been used in device analysis and design, and provided an adequate match to preliminary experimental data. However, with more extensive experimentation over a large range of designs, some results proved to be radically different than predicted, with trends not consistent with effects such as stiction or electrostatic forces. Two different types of behavior, Behavior 1 and Behavior 2, are observed and explained, only one of which is predicted by 2D models. This paper tests the hypothesis that three-dimensional effects can dramatically influence the motion characteristics of FCBMs. Three-dimensional finite element models were constructed, compared to 2D models, and validated for the purpose of testing the hypothesis. Off-axis and eccentric loads are shown to cause behavior consistent with experimental data for Behavior 2.