Micro Motion Amplifiers for Compact Out-of-Plane Actuation

Small-scale, out-of-plane actuators can enable tactile interfaces; however, achieving sufficient actuator force and displacement can require larger actuators. In this work, 2-mm2 out-of-plane microactuators were created, and were demonstrated to output up to 6.3 µm of displacement and 16 mN of blocking force at 170 V. The actuators converted in-plane force and displacement from a piezoelectric extensional actuator into out-of-plane force and displacement using robust, microelectromechanical systems (MEMS)-enabled, half-scissor amplifiers. The microscissors employed two layers of lithographically patterned SU-8 epoxy microstructures, laminated with a thin film of structural polyimide and adhesive to form compact flexural hinges that enabled the actuators’ small area. The self-aligned manufacture minimized assembly error and fabrication complexity. The scissor design dominated the actuators’ performance, and the effects of varying scissor angle, flexure thickness, and adhesive type were characterized to optimize the actuators' output. Reducing the microscissor angle yielded the highest actuator performance, as it maximized the amplification of the half-scissor's displacement and minimized scissor deformation under externally applied loads. The actuators' simultaneously large displacements and blocking forces for their size were quantified by a high displacement-blocking force product per unit area of up to 50 mN·µm/mm². For a linear force–displacement relationship, this corresponds to a work done per unit area of 25 mN·µm/mm². Keywords: microactuators; tactile actuators; piezoelectric actuators; scissor mechanism; motion amplifier; out-of-plane actuato

From Carbon Nanotube Springs to Power MEMS: Creating New Capabilities at the Micro and Nano Scales

Dr. Carol Livermore, Associate Professor in the Department of Mechanical Engineering at MIT presented a lecture at the Nano@Tech Meeting on May 18, 2010 at 12 noon in room 1116 of the Marcus Nanotechnology Building.Runtime: 50:42 minutesCombining new concepts for microsystems with new methods of creating them enables a wide range of small-scale systems. At one extreme, new concepts for power MEMS combined with precision micromachining enable high performance MEMS components for applications from power and energy to high power lasers. At the other extreme, new techniques for micro and nanoscale assembly enable the creation of a wide range of small-scale systems. This talk will present recent research in these and related areas from the Micropower and Nanoengineering Laboratory at MIT. In the MEMS area, the talk will primarily address systems, such as high power MEMS components for lasers. Assembly and applications of large systems of nanoscale components will be addressed as well, including the presentation of techniques for assembling systems of microstructures or cells and discussion of recent experimental and theoretical work on the storage of elastic energy in carbon nanotube springs

Shape-Selective Assembly of Anisotropic, Deformable Microcomponents Using Bottom-Up Micromanufacturing

A technique for shape-selective directed assembly of anisotropic, deformable, chemically-identical microcomponents onto patterned rigid templates based on shape and size differences is modeled and demonstrated. The assembly method not only controls the selective placement of the components, but also aligns the components with the assembly sites. Unlike the assembly of isotropic (spherical) microcomponents, in which only size differences can be used to discriminate among chemically-identical components to achieve selective placement, differences in both shape and size can enable selectivity in the assembly of anisotropic (non-spherical) microcomponents. The present selective directed assembly is driven by shape-matching to a microfabricated template to provide selectivity, uniform chemical surface functionalization to promote assembly, and megasonic excitation to prevent assembly into poorly shape-matched binding sites. A theoretical framework quantifies the predicted selectivity of this approach and predicts that it will be effective for many material combinations, including hydrogels and bio-compatible polymers. Experiments demonstrate successful directed assembly of cylindrical, hydrogel colloidal microcomponents with 26 mu m mean diameter and 50 mu m length into silicon templates patterned with hemicylindrical assembly sites. During the assembly, tapered microcomponents with 150 mu m length and a nominal diameter of 26 mu m that decreases along the components' lengths were successfully excluded from hemicylindrical assembly sites. These results provide the first demonstration of selective directed assembly of non-spherical microcomponents by this approach. The assembly shows high local yields in agreement with theory

Micro Snap-Fits for Latching 3D MEMS Assemblies

This paper reports the design, fabrication and demonstration of micro-scale mechanical latches (micro snapfits) for assembling 3D micro-structures from 2D patterned precursors. The latches consist of pairs of pointy arrowheadlike features mounted on cantilevers, on one membrane, and corresponding slits in the mating membrane. As the membranes are pushed together, the cantilevers bend elastically and squeeze the arrowhead tips through the slits to latch onto the back side of the mating membrane. The latches are reversible, enabling reconfigurable assembly. They are also designed to have no backlash, enabling precise positioning of the assembled structures. An analytical model of the latches was used to design the profile of the arrowheads subject to the geometrical constraints imposed by the alignment system. The micro snapfits were demonstrated by assembling a corner-cube from two folded flat panels with the substrate serving as the third side. Copyright © 2010 by ASME

A Six-Phase Multilevel Inverter for MEMS Electrostatic Induction Micromotors

The construction of miniaturized rotating electric machines through microfabrication techniques is becoming a reality. Applications of such micromotors include miniaturized pumps, compressors, fans, coolers, and turbogenerators. However, the characteristics of these devices make the design of power electronics for them challenging. These characteristics include high-voltage and high frequency operation, tightly constrained operating waveforms and timing, and capacitive input impedances. This paper explores the design of power electronics for microfabricated electrostatic induction machines. We describe the structure and operation of these machines, and establish the operating requirements of power converters for them. We provide a comparison of inverter topologies for this application, and propose an appropriate architecture. The design and experimental evaluation of a prototype six-phase, five-level inverter for this application is presented. The inverter operates at frequencies up to 2 MHz and at voltages up to 300 V, and meets the stringent waveform and timing constraints posed by this application.United States. Defense Advanced Research Projects Agency (Contract DABT63-98-C-0004)United States. Army Research Offic

A Modular, Reconfigurable Microfabricated Assembly Platform for Microfluidic Transport and Multitype Cell Culture and Drug Testing

Modular microfluidics offer the opportunity to combine the precise fluid control, rapid sample processing, low sample and reagent volumes, and relatively lower cost of conventional microfluidics with the flexible reconfigurability needed to accommodate the requirements of target applications such as drug toxicity studies. However, combining the capabilities of fully adaptable modular microelectromechanical systems (MEMS) assembly with the simplicity of conventional microfluidic fabrication remains a challenge. A hybrid polydimethylsiloxane (PDMS)-molding/photolithographic process is demonstrated to rapidly fabricate LEGO®-like modular blocks. The blocks are created with different sizes that interlock via tongue-and-groove joints in the plane and stack via interference fits out of the plane. These miniature strong but reversible connections have a measured resistance to in-plane and out-of-plane forces of up to >6000× and >1000× the weight of the block itself, respectively. The LEGO®-like interference fits enable O-ring-free microfluidic connections that withstand internal fluid pressures of >120 kPa. A single layer of blocks is assembled into LEGO®-like cell culture plates, where the in vitro biocompatibility and drug toxicity to lung epithelial adenocarcinoma cells and hepatocellular carcinoma cells cultured in the modular microwells are measured. A double-layer block structure is then assembled so that a microchannel formed at the interface between layers connects two microwells. Breast tumor cells and hepatocytes cultured in the coupled wells demonstrate interwell migration as well as the simultaneous effects of a single drug on the two cell types

A self-excited MEMS electro-quasi-static induction turbine generator

This paper presents a microfabricated electro-quasi-static (EQS) induction turbine generator that has generated net electric power. A maximum power output of 192 μW [mu W]was achieved under driven excitation. We believe that this is the first report of net-electric-power generation by an EQS induction machine of any scale found in the open literature. This paper also presents self-excited operation in which the generator resonates with an inductor and generates power without the use of external active-drive electronics. The generator comprises five silicon layers, fusion-bonded together at 700 ◦C [degrees C]. The stator is a platinum-electrode structure formed on a thick (approximately 20 μm [mu m]) recessed oxide island. The rotor is a thin film of lightly doped polysilicon also residing on a 10-μm [mu m]-thick oxide island. Carrier depletion in the rotor conductor film limited the performance of the generator. This paper also presents a generalized state-space model for an EQS induction machine that takes into account the machine and its external electronics and parasitics. This model correlates well with measured performance and was used to find the optimal drive conditions for all driven experiments.United States. Army Research Laboratory (DAAD19-01-2-0010)United States. Army Research Office (DAAG55-98-1-0292)United States. Defense Advanced Research Projects Agency (Air Force contract F19628-00-C-0002)Collaborative Technology Alliance In Power And Energy Progra

AmpC hyperproduction in a Cedecea davisae implant-associated bone infection during treatment – a case report and therapeutic implications

Background: Data on antimicrobial resistance mechanisms are scanty for Cedecea spp., with very variable antibiotic resistance patterns documented. Here we report the first in vivo resistance evolution of a C. davisae clinical isolate in a patient with a complex hand trauma and provide insight in the resistance mechanism, leading to therapeutic implications for this pathogen. Case presentation: Cedecea davisae was isolated from a patient with hand trauma during a first surgical debridement. Six days after primary surgical treatment and under antimicrobial treatment with amoxicillin-clavulanic acid and later cefepime, follow up cultures yielded C. davisae which demonstrated a resistance development. The susceptible parental isolate and its resistant derivative were characterized by whole genome sequencing, ampC, ompC and ompF by RT- PCR. The resistant derivative demonstrated an A224G SNP in ampD, the transcriptional regulator of ampC, leading to a His75Arg change in the corresponding AmpD protein. AmpC transcription of the resistant derivative was 362-times higher than the susceptible isolate. Transcription levels of ompF and ompC were 8.5-fold and 1.3-fold lower, respectively, in the resistant derivative. Downregulation of OmpF putatively resulted from a mutation in the presumed promoter region upstream of the dusB-Fis operon, a proposed regulator for ompF. Conclusions: This case demonstrates the in vivo resistance development of C. davisae within 7 days similar to that of the members of the Enterobacter cloacae complex. Our findings add valuable information for future therapeutic management of these opportunistic pathogens as they warrant the same empirical treatment as AmpC producers