MEMS (MicroElectroMechanical Systems) sensors are used in acceleration, flow, pressure and force sensing applications on the micro and macro levels. Much research has focused on improving sensor precision, range, reliability, and ease of manufacture and operation. One exciting possibility for improving the capability of micro sensors lies in exploiting the piezoresistive properties of silicon, the material of choice in many MEMS fabrication processes. Piezoresistivity—the change of electrical resistance due to an applied strain—is a valuable material property of silicon due to its potential for high signal output and on-chip and feedback-control possibilities. However, successful design of piezoresistive micro sensors requires a more accurate model of the piezoresistive behavior of polycrystalline silicon. This study sought to improve the existing piezoresistive model by investigating the piezoresistive behavior of compliant polysilicon structures subjected to tensile, bending and combined loads. Experimental characterization data showed that piezoresistive sensitivity is greatest and mostly linear for silicon members subject to tensile stresses and nonlinear for beams in bending and combined stress states. The data also illustrated the failure of existing piezoresistance models to accurately account for bending and combined loads. Two MEMS force and displacement sensors, the integral piezoresistive micro-Force And Displacement Sensor (FADS) and Closed-LOop sensor (CLOO-FADS), were designed and fabricated. Although limited in its piezoresistive sensitivity and out-of-plane stability, the FADS design showed promise of future application in microactuator characterization. Similarly, the CLOO-FADS exhibited possible feedback control capability, but was limited by control circuit complexity and implementation challenges. The piezoresistive behavior exhibited by the Thermomechanical In-plane Microactuator (TIM) led to a focused effort to characterize the TIM's behavior in terms of force, displacement, actuation current and mechanism resistance. The gathered data facilitated the creation of an empirical, temperature-dependent model for the specific TIM. Based on the assumption of a nearly constant temperature for each current level, the model predicted the force and displacement for a given fractional change in resistance. Despite the success of the empirical model for the test TIM device, further investigation revealed the necessity of a calibration method to enable the model's application to other TIM devices.

The development of current golf club designs has followed an evolutionary process starting with the original wooden heads of a hundred years ago, to the thin-walled, hollow body titanium heads of today. Current designs utilize what has become known as the trampoline effect to increase the efficiency of the ball-club impact, which has a number of limiting factors that restrict clubhead performance. These limitations provided the motivation for this research to explore new mechanisms by which the efficiency of the ball club impact could be increased. In particular this research focuses on the development of compliant mechanisms to increase club performance. The results of this research, from concept development to initial prototype plans, are included in this study. A discussion of past and current research in the area of golf club design is presented. A new list of performance metrics for golf clubs and a number of new golf club concepts is also presented. This is followed by a static and dynamic analysis of the most promising golf club configuration. The study is concluded with a concept validation analysis and a presentation of possible prototype configurations for a new golf club design.

Feedback control of MEMS devices has the potential to significantly improve device performance and reliability. One of the main obstacles to its broader use is the small number of on-chip sensing options available to MEMS designers. A method of using integrated piezoresistive sensing is proposed and demonstrated as another option. Integrated piezoresistive sensing utilizes the inherent piezoresistive property of polycrystalline silicon from which many MEMS devices are fabricated. As compliant MEMS structures flex to perform their functions, their resistance changes. That resistance change can be used to transduce the structures' deflection into an electrical signal. This dissertation addresses three topics associated with integrated piezoresistive sensing: developing an empirical model describing the piezoresistive response of polycrystalline-silicon flexures, designing compliant MEMS with integrated piezoresistive sensing using the model, and implementing feedback control using integrated piezoresistive sensing. Integrated piezoresistive sensing is an effective way to produce small, reliable, accurate, and economical on-chip sensors to monitor compliant MEMS devices. A piezoresistive flexure model is presented that accurately models the piezoresistive response of long, thin flexures even under complex loading conditions. The model facilitates the design of compliant piezoresistive MEMS devices, which output an electrical signal that directly relates to the device's motion. The piezoresistive flexure model is used to design a self-sensing long displacement MEMS device. Motion is achieved through contact-aided compliant rolling elements that connect the output shaft to kinematic ground. Self-sensing is achieved though integrated piezoresistive sensing. An example device is tested that demonstrates 700 micrometers of displacement with a sensing resolution of 2 micrometers. The piezoresistive microdisplacement transducer (PMT) is a structure that uses integrated piezoresistive sensing to monitor the output displacement of a thermomechanical inplane microacutator (TIM). Using the PMT as a feedback sensor for closed-loop control of the TIM reduced the system's response time from 500~$mu$s to 190~$mu$s, while maintaining a positioning accuracy of $pm$29~nm. Feedback control of the TIM also increased its robustness and reliability by allowing the system to maintain its performance after it had been significantly damaged.

Compliant bistable micromechanisms have been proposed for use in applications such as switches, relays, shutters, and sensing arrays. Unpublished laboratory testing suggests that off-axis forces may affect the bistable nature of fully compliant bistable micromechanisms (FCBMs). The actuation forces required to snap the FCBM from one stable equilibrium position to another can be altered if the off-axis forces are applied to the mechanism during transition between stable positions. Understanding the three-dimensional characteristics of these mechanisms and the effect of eccentric loading conditions would be helpful in design and analysis of FCBMs. Two 3-D FEA models were developed for analysis and validation purposes. The 3-D solid element model includes great detail regarding the geometry and boundary conditions of the FCBMs. Including fillets, residual stress, and anchors proved to generate more accurate results. The 3-D beam element model is greatly simplified, and primarily used to validate the results produced by the 3-D solid element model. Both models were validated through comparison to experimental data. A test suite of FEA runs was constructed to better understand the 3-D behavior of FCBMs. A chief discovery provided by the test suite results was the existence of two phenomenon conditions, defined as Phenomenon 1 and Phenomenon 2. Phenomenon 1 tended to occur when smaller off-axis forces were included in the model. When comparing the two phenomenon, larger pitch rotation, smaller out-of-plane motion, larger reaction forces, and a more consistent bistable mechanism was associated with Phenomenon 1. Phenomenon 2 tended to occur when larger applied forces were included in the model. Once this phenomenon was generated, the FCBM tended to remain in this condition. Reduced reaction forces, larger out-of-plane motion, and a tendency of non-bistability were characteristics of this phenomenon. The FCBMs could experience much larger in-plane applied forces before transitioning to Phenomenon 2. In contrast, relatively small out-of-plane forces caused the same transition. The FCBMs proved to be well behaved when being pulled into their alternate stable position rather than being pushed. A pushing motion caused the shuttle to roll, pitch and yaw in an inconsistent manner.

Constant-force mechanisms are mechanical devices that provide a near-constant output force over a prescribed deflection range. This thesis develops various optimization-based methods for designing robust constant-force mechanisms. The configuration of the mechanisms that are the focus of this research comprises a cam and a compliant spring fixed at one end while making contact with the cam at the other end. This configuration has proven to be an innovative solution in several applications because of its simplicity in manufacturing and operation. In this work, several methods are introduced to design these mechanisms, and reduce the sensitivity of these mechanisms to manufacturing uncertainties and frictional effects. The mechanism's sensitivity to these factors is critical in small scale applications where manufacturing variations can be large relative to overall dimensions, and frictional forces can be large relative to the output force. The methods in this work are demonstrated on a small scale electrical contact on the order of millimeters in size. The method identifies a design whose output force is 98.20% constant over its operational deflection range. When this design is analyzed using a Monte Carlo simulation the standard deviation in constant force performance is 0.76%. When compared to a benchmark design from earlier research, this represents a 34% increase in constant-force performance, and a reduction from 1.68% in the standard deviation of performance. When this new optimal design is evaluated to reduce frictional effects a design is identifed that shows a 36% reduction in frictional energy loss while giving up, however, 18.63% in constant force.

Fully compliant bistable mechanisms have been proposed to be used as threshold accelerometers. The advantages to using these devices are that they require no external power to operate and maintain their sensing state. Using this characteristic the devices can be integrated with passive radio frequency identification tags (RFID). This allows for the sensing package to lay dormant with no maintenance needed until the sensor is read by the RFID reader. This thesis presents a successfully fabricated and integrated threshold accelerometer with a passive RFID tag. This in turn has been successfully read with an RFID reader and shown to act as a wireless passive sensor indicating whether or not a threshold acceleration has been exceeded. It is shown that in general plastics are not a suitable material to use in threshold accelerometers due to variability in fabrication, temperature and prolonged stresses inducing stress relaxation in the material. Multiple methods for testing the switching forces of these threshold accelerometers are developed and a frequency response for the switching forces of these devices is explored. A straight-leg bistable mechanism design model is introduced and used to design metal bistable devices to reduce the variations seen in the plastic threshold accelerometers. With this metal design a new fabrication process is introduced to attain thin metal compliant flexures with little variation in the thickness of the compliant flexures. This method allows for a more economical method of producing compliant flexures. The metal bistable mechanism designs presented show significant improvement over the plastic bistable designs. These improvements include minimizing the effects of stress relaxation, minimizing variation in switching forces and minimizing variation between fabricated devices. The cost, however, with the metal bistable mechanism design would be more than the plastic bistable mechanism design.

Proper positioning of Microelectromechanical Systems (MEMS) components influences the functionality of the device, especially in devices where the motion is in the range of hundreds of micrometers. There are two main obstacles to positioning: off-axis displacement, and position determination. This work studies four large-displacement devices, their axial and transverse stiffness, and piezoresistive response. Methods for improving the device characteristics are described. The folded-beam suspension, small X-Bob, large X-Bob and double X-Bob were characterized using non-dimensional metrics that measure the displacement with regard to the size of the device, and transverse stiffness with regard to axial stiffness. The stiffness in each direction was determined using microprobes to induce displacement, and microfabricated force gauges to determine the applied force. The large X-Bob was optimized, increasing the transverse stiffness metric by 67%. Four-point resistance testing and microprobes were used to determine the piezoresistive response of the devices. The piezoresistive response of the X-Bob was maximized using an optimization routine. The resulting piezoresistive response was over seven times larger than that of the initial design. Piezoresistive encoders for ratcheting actuation of large-displacement MEMS are introduced. Four encoders were studied and were found to provide information on the performance of the ratcheting actuation system at frequencies up to 920 Hz. The PMT encoder produced unique signals corresponding to distinct ideal and non-ideal operation of the ratchet wheel actuation system. Encoders may be useful for future applications which require position determination.

A deeper understanding of human development and disease is made possible partly through the study of genetically modified model organisms, such as the common mouse (Mus musculus). By genetically modifying such model organisms, scientists can activate, deactivate, or highlight particular characteristics. A genetically modified animal is generated by adding exogenous (foreign) genetic material to one or more embryonic cells at their earliest stages of development. Frequently, this exogenous genetic material consists of specially engineered DNA, which is introduced into a fertilized egg cell (zygote). When successfully introduced into the zygote, the exogenous DNA will be incorporated into the cell's own genome, and the animal that develops from the zygote will exhibit the genetic modification in all of its cells. The current devices and methods for generating genetically modified animals are inefficient, and/or difficult to use. The most common and efficient method for inserting new DNA into zygotes is by directly injecting a DNA solution through a tiny glass tube into the cell in a process called microinjection. Unfortunately, microinjection is quite inefficient (success rates are commonly between 1 and 5%), but often it is the only method for inserting DNA into eggs, zygotes, or early stage embryos. This thesis presents the design and testing of a micrometer sale, pumpless microelectromechanical system (MEMS) nanoinjector. Rather than use pumps and capillaries, the nanoinjector employs electrostatic charges to attract and repel DNA onto and off of the surface of a solid lance. The nanoinjector also includes a mechanical system for constraining the target cells during injection. Initial testing indicates the nanoinjector does not decrease cell viability, and it has a very high initial success rate (up to 90%). With the addition of an on-chip actuator, the nanoinjector could be packaged as an inexpensive, fully automated system, enabling efficient, high volume genetic modification of developing animals. Such a device would greatly increase the ease and speed of generating the model organisms needed to study such critical diseases such as Alzheimer's disease, cancer, and diabetes.

This thesis introduces new revolute and torsional lamina emergent mechanism (LEM) flexure designs that are suited for use in metals. Previous LEM flexures have been designed for use in highly elastic materials, such as polymers. In extending LEM flexure designs to metals, a LEM flexure design criteria is also introduced. The LEM flexure criteria is based on relative performance between the LEM flexure and a performance datum which the LEM flexure must improve upon. This performance datum, or benchmark, is a section of lamina that is of the same overall length, width, and thickness as the LEM flexure. An analysis of the revolute and torsional metal LEM flexures, based on the LEM flexure criteria, is performed and both are found to successfully meet the criteria. A brief comparative performance study is also carried out between a basic crank-slider mechanism to which the revolute and torsional metal LEM flexures have and have not been applied. The revolute and torsional metal LEM flexures are found to improve the crank-slider performance.

Limited resources are currently available to assist engineers in implementing compliant members into mechanical designs. As a result, engineers often have little to no direction incorporating compliant mechanisms. This thesis develops a conceptual design framework and process that utilizes a proposed classification scheme and a library of mechanisms to help engineers incorporate compliant mechanisms into their applications. As the knowledge related to the synthesis and analysis of compliant mechanisms continues to grow and mature, and through the classification scheme established in this thesis, compliant mechanisms may become more extensively used in commercial mechanical designs. This thesis also demonstrates a design approach engineers can use to convert an existing rigid-body mechanism into a compliant mechanism by using the established classification scheme and a library of compliant mechanisms. This approach proposes two possible techniques that use rigid-body replacement synthesis in conjunction with a compliant mechanism classification scheme. One technique replaces rigid-body elements with a respective compliant element. The other technique replaces a complex rigid-body mechanism by decomposing the mechanism into simpler functions and then replacing a respective rigid-body mechanism with a compliant mechanism that has a similar functionality. These techniques are then demonstrated by developing and designing a competitive and feasible compliant road bicycle brake system.