Flexible electronics have gained great attention recently. Applications such as flexible displays, artificial skin and health monitoring devices are a few examples of this technology. Looking closely at the components of these devices, although MEMS actuators and sensors can play critical role to extend the application areas of flexible electronics, fabricating movable MEMS devices on flexible substrates is highly challenging. Therefore, this thesis reports a process for fabricating free standing and movable MEMS devices on flexible silicon substrates; MEMS flexure thermal actuators have been fabricated to illustrate the viability of the process. Flexure thermal actuators consist of two arms: a thin hot arm and a wide cold arm separated by a small air gap; the arms are anchored to the substrate from one end and connected to each other from the other end. The actuator design has been modified by adding etch holes in the anchors to suit the process of releasing a thin layer of silicon from the bulk silicon substrate. Selecting materials that are compatible with the release process was challenging. Moreover, difficulties were faced in the fabrication process development; for example, the structural layer of the devices was partially etched during silicon release although it was protected by aluminum oxide which is not attacked by the releasing gas . Furthermore, the thin arm of the thermal actuator was thinned during the fabrication process but optimizing the patterning and etching steps of the structural layer successfully solved this problem. Simulation was carried out to compare the performance of the original and the modified designs for the thermal actuators and to study stress and temperature distribution across a device. A fabricated thermal actuator with a 250 μm long hot arm and a 225 μm long cold arm separated by a 3 μm gap produced a deflection of 3 μm before silicon release, however, the fabrication process must be optimized to obtain fully functioning devices on flexible silicon.

This thesis explores a method to fabricate magnetic membranes with asymmetric distribution of particles and their testing as actuators. Focus of this research is to fabricate thin polymeric sheets and thickness range of 120-125µm, with asymmetric distribution of magnetic nano particles, employing micromagnets during the fabrication. The micromagnets are used to localize the magnetic particles during the curing process at selected locations. The effect of the asymmetric distribution of magnetic particles in the membrane is used for the first time. Magnetite (Fe3O4) is used as the magnetic particles that is embedded into a polymeric membrane made of polydimethylsiloxane (PDMS); the membrane is then tested in terms of deflection observed by using a high-resolution camera. From the perspective of the biomedical application, PDMS is chosen for its excellent biocompatibility and mechanical properties, and Fe3O4 for its non-toxic nature. Since magnetic actuation does not require onboard batteries or other power systems, it is very convenient to use in embedded devices or where the access is made difficult. A comparative study of membranes with asymmetric and randomly distributed particles is carried out in this thesis. The asymmetric distribution of magnetic particles can benefit applications involving localized and targeted treatments and precision medicine.

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The proteins wheat gluten and gelatin were tested for use in biocomposites and soft actuating materials, respectively. In Chapter II, the self-assembly mechanism of trypsin hydrolyzed wheat gluten (THWG) into rigid β-sheets was applied to an aqueous polyvinyl alcohol (PVA) environment. Aqueous PVA was used in order to determine the effects of an aqueous environment other than pure water on THWG self-assembly kinetics and to realize the potential use of THWG as a nanofiller in polymer matrices. THWG was able to self-assemble into anisotropic spikes and agglomerates of spikes called "pompons" through hydrophobic interactions. THWG self-assembly kinetics were retarded in aqueous PVA solutions compared to water, with the highest molecular weight PVA solution showing the slowest self-assembly kinetics. Chapters III and IV explore the potential of gelatin hydrogels for use in soft actuators. A gelatin bilayer system was designed where an active layer swelled more than a passive layer to cause the system to bend/actuate in response to an environmental stimulus. In Chapter III, gelatin layers were chemically crosslinked to different degrees with glutaraldehyde to achieve bilayer bending when placed in water. Curvature of the bilayer system was found to be dependent on the difference in volume swell ratio between the two layers. It was determined that maximum bending occurred when the passive layer swelled to 60% of the swelling of the active layer. Addition of pre-gelatinized starch to the active layer increased layer swelling and bilayer curvature. Treating the starch containing bilayer with -amylase returned the bilayer to its original shape. In Chapter IV, a pH responsive gelatin bilayer was constructed using Type A and Type B gelatin. Type A and Type B gelatin gels had different chemical properties and swelled to different volumes based on the gel solution pH. Bilayers constructed from Type A and Type B gelatin exhibited different degrees of bending when placed in various pH solutions with maximum curvature occuring at pH 10. A cyclic actuator could be formed when the bent bilayers were placed in a minimum of 0.01M NaCl solution. Placement in salt solution resulted in the unbending of the bilayer. Overall, this work demonstrated the various applications of proteins as functional and green materials. / Doctor of Philosophy / The majority of plastics consist of synthetic polymers derived from oil that cannot be broken down by the environment (i.e., not biodegradable). Research is underway to develop sustainable, biodegradable materials. Proteins are a biological polymer that have a wide range of chemical, structural, and functional properties; for this reason they are an excellent source material for use in the design of environmental friendly materials. In Chapter II, the ability of wheat gluten protein to self-assemble into rigid, nanosized structures is used to explore the potential of the protein to be used as a biodegradable nanofiller. A nanofiller is added to various materials in order to improve the overall mechanical properties of the material. Wheat gluten is self-assembled in an aqueous polymer environment. The results show that the polymer environment stunts or slows down the self-assembly rate of the protein compared to a pure water environment. Nanometer sized spikes form in the polymer solutions, indicating wheat gluten could be used as a nanofiller in certain materials. Chapters III and IV explore the use of gelatin proteins for applications in soft robotics. Soft robots and their moveable parts, called soft actuators, are deformable and respond to changes in the environment such as pH, light, temperature, etc. For this reason, soft robots are considerable adaptable compared to traditional rigid robots. Designing a soft actuator from gelatin gels would result in a “smart” material that is biocompatible and biodegradable. A gelatin soft actuator is created using a bilayer design in which one layer of the bilayer swells more than the other layer causing the entire system to bend/actuate. Depending on how the bilayer system was fabricated, bending could be achieved based on stimuli such as the presence of water, the presence of a substrate and enzyme, and changes in pH. Overall, this dissertation demonstrates the extraordinary potential for the use of proteins in designing sustainable materials.

A piezoceramic actuator used for structural control behaves electrically as a nearly pure capacitance. When conventional amplifiers are used to drive these actuators, the current and voltage is close to 90 degrees out of phase. This causes the power factor (PF) of the load to be close to zero and results in excessive power requirements. This thesis reports the results of a study of the following question: What effect does applying power factor correction methods to piezoceramic actuators have on their power consumption characteristics? A subproblem we explored was to detennine the qualitative relationship between the power consumption of a piezoceramic actuator and the damping that actuator added to a structure. To address the subproblem, a feedback control experiment was built which used a ceramic piezoceramic actuator and a strain rate sensor configured to add damping to a cantilevered beam. A disturbance was provided by a shaker attached to the beam. The power consumption of the actuator was determined by measuring the current and voltage of the signal to the actuator. The energy dissipated in the beam by the feedback control loop was assumed to be modeled by an ideal structural damping model. A model relating structural damping as a function of the apparent power consumed by the actuator was developed, qualitatively verified, and physically justified. Power factor correction methods were employed by adding an inductor in both parallel to and in series with the piezoceramic actuator. The inductance values were chosen such that each inductor-capacitor (LC) circuit was in resonance at the second natural frequency of the beam. Implementing the parallel LC circuit reduced the current consumption of the piezoceramic actuator by 75% when compared to the current consumption of the actuator used without an inductor. Implementing the series LC circuit produced a 300% increase in the voltage applied to the actuator compared to the case when no inductor was used. In both cases, employing power factor correction methods corrected the power factor to near unity and reduced the apparent power by 12 dB. A theoretical model of each circuit was developed. The analytical and empirical results are virtually identical. The results of this study can be used to synthesize circuits to modify piezoceramic actuators, reducing the voltage or current requirements of the amplifiers used to drive those actuators / Master of Science

In this thesis, the proof-mass actuator is studied for vibration suppression of a flexible structure. While these actuators have a favorable force-to-weight ratio, the finite travel of the proof-mass, called the stroke length, imposes restrictions on the use of the actuator. This restriction implies that the actuator has a finite operating region in terms of initial conditions on the state. This operating region, along with the amount of vibration suppression potential, defines the performance of the actuator. To increase the performance, nonlinear control is proposed. These control laws monitor the position and velocity of the proof-mass and apply a large restoring force whenever the proof-mass is in danger of breaking its stroke limit. A harmonic balance analysis concludes that these nonlinear control laws do not induce limit cycles. The performance of actuators with different parameters is also compared. A relation is presented that associates the modal frequency of the structure to these parameters. It is also found that large stroke with small mass offers the best performance with the nonlinear control in place. / Master of Science

This work discusses the design of, and initial experiments with, a MIMO plate control testbed. This structure will be used as a development and standard comparison site for AVC and ASAC and is an extension of previous SIMO control investigations which used accelerometers and shakers. This portion of the development process of the MIMO plate control testbed is concerned with actuator and sensor materials and architecture, modeling approaches and requirements, and initial control experiments. The piezoelectric sensors and actuators are arranged on the plate to control the first five vibration modes. The sensors measure plate positions using a high impedance signal conditioning amplifier. The sixteen-channel design implements a band-pass filter to eliminate low- and high-frequency noise. The power amplification scheme chosen for the actuators uses low-gain amplifiers (~2.5 V/V) in series with a transformer (24:1) to deliver high voltages (up to 150 V) to the actuators. Low-pass smoothing filters (200 Hz cutoff) were added on the control inputs to reduce the high frequency content of the zero-order-held digital control signal. Initial methods for system identification of piezostructures are presented. Parametric frequency response approaches (modal analysis) were used and the model achieved is compared with measured data and purely analytic models. The empirical model was used in initial SIMO control experiments to demonstrate the testbed closed-loop performance. A LQG controller was implemented and produced 6 dB of suppression for the second mode for a 110 Hz disturbance. / Master of Science

In this thesis, a method of predicting the steady state, dynamic, electromechanical behavior of stack actuators (both electrostrictive and piezoelectric) integrated within complex structures is developed and experimentally verified. This research was motivated by a need to accurately predict transmission force, velocity output, and power consumption for a wide range of applications both terrestrial and space based. The relevant transduction equation / parameters are derived from basic principles. These results are experimentally verified with a PZT stack active member. The derivations are then extended to incorporate the effects of integrating the actuator within a host structure. Specifically, the equations needed to predict actuator output force, resulting velocity and drawn current are derived. To implement and test these results in a structure, the equivalent host structure impedance must be determined. This is done experimentally for a complex truss structure representative of a small satellite. These results are then used to prepare theoretical predictions which compare well with experimentally measured output force. Finally, the derivations are extended to the electrical behavior of active members integrated within truss structures. It is now possible to predict the electrical load imposed by the active member on the power supply system including the effects of coupling with the host structure dynamic boundary conditions. Two implications of this are considered. First, the required power demands directly influence the design and sizing of amplifiers, applied voltage levels and power systems. Second, the dissipative power from actuation losses contributes directly towards raising the internal temperature of an operating stack actuator. / Master of Science