This thesis work provides an insight into the design of Force-amplifying Compliant Mechanisms (FaCMs) that are integrated with micromachined resonant accelerometers to increase their sensitivity. An FaCM, by mechanically amplifying the inertial force, enhances the shift in the resonance frequency of the beams used for sensing the acceleration whose effect causes an axial force on the beams. An extensive study on different configurations of resonators namely, single beam resonator, single-ended tuning fork (SETF), and double-ended tuning fork (DETF), is carried out to gain insights about their resonant behavior. The influence of the boundary conditions on the sensor’s sensitivity emerged from the study. We found that not only the force-amplification factor but also the multi-axial stiffness of the FaCM and proof-mass influence the resonance frequency of the resonator as well as the bandwidth of the modified sensor for certain configurations but not all. Thus, four lumped parameters were identified to quantify the effectiveness of an FaCM. These parameters determine the boundary condition of the sensing beams and also the forces and the moment transmitted to them. Also presented in this work is a computationally efficient model, called the Lumped Parameter Model (LPM) for evaluation of the sensitivity. An analytical expression for the frequency-shift of the sensing resonator beams is obtained by considering the FaCM stiffness parameters as well as the lumped stiffness of the suspension of the inertial mass. Various FaCMs are evaluated and compared to understand how the four lumped parameters influence the sensor’s sensitivity. The FaCMs are synthesized using topology optimization to maximize the net amplification factor with the volume constraint. One of the FaCMs outperforms the lever by a factor of six. Microfabrication of resonant accelerometer coupled with FaCM and comb-drive actuator is carried out using a silicon-on-insulator process. Finally, the selection map technique, a compliant mechanism redesign methodology is used for enhancing the amplification of FaCMs. This technique provides scope for further design improvement in FaCMs for given sensor specifications.

[pt] Ao contrário dos mecanismos tradicionais, um mecanismo flexível conta com a deflexão de seus membros flexíveis para gerar movimento, ao mesmo tempo que apresenta vantagens como a desnecessidade de lubrificação e uma montagem mais fácil. Um mecanismo flexível de mola orto-planar foi analisado neste trabalho e seu desempenho mecânico após testes de envelhecimentos higrotérmicos e com radiação ultravioleta foram estudados. A análise do envelhecimento aqui realizada aborda o desempenho de mecanismos flexíveis após processos de envelhecimentos que pdoe ajudar no desenvolvimento de futuros mecanismos flexíveis. Amostras de tração ASTM D638 tipo I também foram submetidas aos envelhecimentos para servir de comparação para as amostras de mola orto-planar. As amostras foram submetidas a três tipos diferentes de envelhecimento, a saber: imersão em água, imersão em óleo e radiação ultravioleta. Os testes de envelhecimento por imersão em líquido foram realizados em três níveis de temperaturas: temperatura ambiente, 50 graus C e 70 graus C. Em geral, as amostras de tração mostraram mudanças estatísticas significativas no módulo de Young e no deformação na ruptura, enquanto as amostras de mola orto-planar não apresentaram alterações estatísticas importantes em nenhuma condição de envelhecimento, o que indica que as propriedades mecânicas e capacidades elásticas dos mecanismos não foram afetadas pelos processos de envelhecimento. Embora mais testes com os materiais específicos, ambiente e tempo de exposição sejam necessários para verificar o uso em uma aplicação específica, os resultados deste estudo sugerem que os mecanismos flexíveis mostram a promessa de uso em aplicações onde o envelhecimento é uma preocupação e sua vida é esperada estar dentro dos limites deste estudo de envelhecimento. / [en] In contrast to traditional mechanisms, a compliant mechanism relies on the deflection of its flexible members to generate motion, while presenting advantages such as no need for lubrication and easier assembly. An ortho-planar spring (OPS) compliant mechanism was analyzed in this work and its mechanical performance after hygrothermal and ultraviolet radiation aging tests was studied. The aging analysis performed here addresses the performance of compliant mechanisms after aging processes that can help in the design of future compliant mechanisms. ASTM D638 tensile test type I samples were also subjected to aging to serve as a comparison for OPS samples. The samples were subjected to three different types of aging conditions, namely water immersion, oil immersion and ultraviolet radiation. The liquid immersion aging tests were performed in three temperature levels: room temperature, 50 C degrees and 70 C degrees. In general, tensile samples showed significant statistical changes in Young s modulus and elongation at break, while OPS samples did not present considerable statistical change in any aging condition, which indicate that the mechanical properties and elastic capabilities of OPS samples were not affected by aging processes. Although more testing with the specific materials, environment, and exposure time would be required to verify its use in a specific application, the findings of this study suggest that compliant mechanisms show promise for use in applications where aging is a concern, and their life is expected to be within the limits of this aging study.

This work explores the use of carbon-infiltrated carbon nanotube (CI-CNT) forests as a material for fabricating compliant MEMS devices. The impacts of iron catalyst layer thickness and carbon infiltration time are examined. An iron layer of 7nm or 10nm with an infiltration time of 30 minutes produces CI-CNT best suited for compliant applications. Average maximum strains of 2% and 2.48% were observed for these parameters. The corresponding elastic moduli were 5.4 GPa and 4.1 GPa, respectively. A direct comparison of similar geometry suggested CI-CNT is 80% more flexible than single-crystal silicon. A torsional testing procedure provided an initial shear modulus of about 5 GPa for the 7-nm, 30-min CI-CNT. The strain and elastic modulus values were used to design numerous functional devices which were then fabricated in CI-CNT. A series of compliant cell restraint mechanisms were developed, assessed, and revised. A passive restraint with no moving parts was found to be both the most effective design and the easiest design to produce economically. A refined version of the passive restraint has been released commercially. Another series of designed devices successfully demonstrates the implementation of CI-CNT LEM designs.

No description available.

Simultaneously achieving high-sensitivity and a large resonance frequency of micromachined accelerometers is difficult because of the inherent trade-off between the two. In this thesis, we present a mechanical displacement-amplifying technique that is amenable to micromachining to enhance sensitivity without compromising on the resonance frequency and cross-axis sensitivity. Depending on the requirements of sensitivity alone or sensitivity and resonance frequency, Displacement-amplifying Compliant Mechanisms (DaCMs) are designed using the selection map-based technique, which indicates the limits of what is possible for given specifications on size and microfabrication. In order to prove the benefits of a DaCM, we modified the designs of two very sensitive capacitive micromachined accelerometers from the literature by incorporating DaCMs and showed that, within the same footprint on the chip, the displacement sensitivity could be enhanced by more than 60% while the resonance frequency was also improved by more than 30%. As the focus of the thesis is to explore the integration of DaCMs into accelerometers, the analytical, computational, and practical aspects are discussed in detail. Both single and dual axis in-plane accelerometers are considered. The fabrication processes used are Silicon-on-Insulator Multi-user MEMS Processes (SOIMUMPs) and a customized Silicon-on-Insulator (SOI) based process. The fabricated accelerometers are packaged and brought to the product form. They were tested at the die level as well as in the packaged form. Under dynamic conditions, the measured amplification factor of the fabricated single-axis in-plane accelerometer was observed to be 11. The overall dimension of the accelerometer was 4.25 mm × 1.25 mm. The first in-plane natural frequency of the fabricated accelerometer was found to be 6.25 kHz. The voltage sensitivity of the packaged accelerometer with the DaCM measured 26.7 mV/g at 40 Hz with differential capacitance sensitivity of 3926 ppm/g around the base capacitance of 0.75 pF. The fabricated dual-axis accelerometer has a special configuration of twelve folded-beam suspension blocks that de-couple any displacements along the two in-plane orthogonal axes. The decoupling feature is retained even after adding the DaCMs along both the axes. The total device size was 8.6 mm × 8.6 mm. The device was also fabricated and packaged inside a ceramic flat-pin package using hybrid die-to-die wire-bonding. Die-level dynamic characterization showed that the average geometric advantage achieved using the DaCMs is 6.2 along both the in-plane axes. The measured axial voltage sensitivity of about 580 mV/g for both the axes was achieved with a cross-axial sensitivity of less than 2% and a natural frequency of 920 Hz. The static capacitance sensitivity was found to be 0.296 × 106 ppm/g with a base capacitance of 0.977 pF. Also presented in this work is a wide-band dual-axis accelerometer without an amplifying mechanism. Its first two in-plane modal frequencies measured 14.2 kHz. The measured sensitivity of the packaged accelerometer along both the axes of the device was found to be 62 mV/g at 200 Hz. Aiming at towards cost-effective accelerometers for small-volume markets, we also developed a single-axis and two dual-axis meso-scale spring-steel in-plane accelerometers equipped with Allegro A1395 linear Hall-effect sensors for sensing the displacement of the proof-mass. The single-axis in-plane meso-scale accelerometer also contains a DaCM. It is observed through simulation that the single-axis design with a DaCM is 39% more sensitive and has 41% more bandwidth compared to a single-axis design without a DaCM. The measured sensitivity of the fabricated single-axis spring-steel accelerometer with a DaCM was found to be 71.4 mV/g with a minimum resolvable acceleration of 14 milli-g. The unique features of the first generation of dual-axis accelerometers are that a rechargeable Li-ion battery adds to the proof-mass. It also contains a de-coupling mechanism that can decompose any planar acceleration into its axial components. The second generation of dual-axis accelerometers is more compact in size. All the mechanical elements of the accelerometers are made of EN J42/AISI 1080 spring steel foil machined using Wire-cut Electro-Discharge- Machining. The measured sensitivity of the first generation of dual-axis meso-scale accelerometers is 78 and 108 mV/g along the X and Y axes whereas the second generation device exhibits a sensitivity of 40 mV/g for both the axes. The thesis concludes that the sensitivity of a displacement-based sensor can be improved using a suitably designed DaCM without compromising the resonance frequency and hence the bandwidth. Furthermore, the work describing the development of meso-scale accelerometers also establishes spring steel as a viable material for meso-scale applications.

Miniature compliant grippers are designed and developed to manipulate biological cells and characterize them. Apart from grippers, other compliant mechanisms are also demonstrated to be effective in manipulation and characterization. Although scalability and force-sensing capability are inherent to a compliant mechanism, it is important to design a compliant mechanism for a given application. Two techniques based on Spring-lever models and kinetoelastostatic maps are developed and used for designing compliant devices. The kinetoelastostatic maps-based technique is a novel approach in designing a mechanism of a given topology and shape. It is also demonstrated that these techniques can be used to tune the stiffness of a mechanism for a given application. In situations where any single mechanism is incapable of executing a specific task, two or more mechanisms are combined into a single continuum with enhanced functionality. This has led to designs of composite compliant mechanisms. Biological cells are manipulated using compliant grippers in order to study their mechanical responses. Biological cells whose size varies from 1 mm (a large zebrafish embryo) to 10 µm (human liver cells), and which require the grippers to resolve forces ranging from 1 mN (zebrafish embryo) to 10 nN (human cells), are manipulated. In addition to biological cells, in some special cases such as tissue-cutting and cement-testing, inanimate specimens are used to highlight specific features of compliant mechanisms. Two extreme cases of manipulation are carried out to demonstrate the efficacy of the design techniques. They are: (i) breaking a stiff cement specimen of stiffness 250 kN/m (ii) gentle grasping of a soft zebrafish embryo of stiffness 10 N/m. Apart from manipulation, wherever it is viable, the mechanisms are interfaced with a haptic device such that the user’s experience of manipulation is enriched with force feedback. An auxiliary study on the characterization of cells is carried out using a micro¬pipette based aspiration technique. Using this technique, cells existing in different conditions such as perfusion, therapeutic medicines, etc., are mechanically characterized. This study is to qualitatively compare aspiration-based techniques with compliant gripper-based manipulation techniques. A compliant gripper-based manipulation technique is beneficial in estimating the bulk stiffness of the cells and can be extended to estimate the distribution of Young’s modulus in the interior. This estimation is carried out by solving an inverse problem. A previously reported scheme to solve over specified boundary conditions of an elastic object—in this case a cell—is improved, and the improved scheme is validated with the help of macro-scale specimens.

This thesis deals with the design of two-axis displacement-amplifying compliant mechanisms (DaCMs) using topology optimization. The two-axis compliant mechanisms considered here are XY positioners and two-axis inertial sensors. A building block approach, with several single-axis DaCMs as building blocks, is used to conceive designs of compliant platforms that provide two orthogonal and independent movement of a common platform. Spring-mass-lever (SML) models of these designs are developed to simplify the analysis and design of the complicated arrangements of building blocks. The XY positioners designed in this work have perfectly de-coupled motion without compromising on the frequency; the best design of the stage has a displacement amplification of five resulting in the enhanced range of 4.2 % of the mechanism size–a significant improvement from the 1.67 %, the maximum range of the designs reported so far. Nearly 100% improvement is observed in the sensitivity of the two-axis accelerometer as compared with an existing design that occupied the same area. Multiple prototypes of XY positioners were fabricated on polypropylene sheets using CNC machining; and on spring steel and aluminium using wire-cut electro discharge machining. Mask layouts for two-layer two-axis accelerometers are designed for micro-fabrication using reactive ion etching and wafer bonding.