In this work, the opto-piezo actuation and piezoelectric actuation in gallium arsenide (GaAs) is experimentally and theoretically verified. Experimentally the response of the respective actuations are measured using the current generated from the inverse piezoelectric effect. The mechanical structure used to generate this current is a micron size torsional resonator fabricated from a GaAs photodiode heterostructure. The photodiode heterostructure is optically and electrically designed as a photovoltaic (PV) cell while mechanically the structure resembles a bimorph. The bimorph design is a result of the PV cell consisting of a pn junction and a heterojunction where the depletion regions have the additional property of being piezoelectric. The opto-piezo actuation results from using the photogenerated voltage to piezoelectrically drive a mechanical structure. Using light modulated at the resonance frequency of the torsional resonator the measured current is shown to linearly increase with intensity. For the electrical actuation case, the torsional resonator is driven using the non- linear response of the pn junction to an applied voltage. The non-linear response results in generation of voltage at the harmonic frequencies of the applied voltage. The voltage generated at twice the applied frequency is given the label 2f and is used to piezoelectrically drive the mechanical structure. The above results for the two methods of actuation are theoretically validated by deriving a model for the expected current. The model predicts the current as a function of the voltage. For the opto-piezo case this voltage is the photovoltage. The photovoltage is determined using the AC PV model. This model is derived using the DC PV model and predicts the AC operation of a photodiode in the 3rd and 4th quadrants to resistive and reactive loads. Using the opto-mechanical coupling coefficient the efficiency of the opto-piezo actuation is compared to opto-thermal actuation and radiation pressure actuation. It is shown that the opto-piezo effect, in general, is several orders of magnitude better than the other two in converting optical energy into mechanical energy. This is an important result because in situations where low optical powers are only available and power, in general, cannot be spared, for e.g. on a satellite, devices that make use of the opto-piezo effect could be used for either actuation or sensing. Generally however, using the opto-piezo effect can lead to either integration of existing photonic devices with mechanical resonators or new photonic devices all together. For e.g. using the opto-piezo effect an adaptable optical correlator can be made which could be used to make artificial intelligent machines. / Thesis / Doctor of Philosophy (PhD)

Thesis (M.B.A.)--Boston University / From that eventful day in 1750 When electrical current was first discovered and through the succeeding years Where such famous inventions as the electric light, the telephone, and generation of alternating current, were brought into being, to this present age of electronic development, the electro~echanical aids available to industrial management have mounted in number. Many of the basic inventions of the Nineteenth Century, although they have been improved steadily, are accepted as commonplace. Take for instance, the telephone or the electric light, little thought is given to their importance in everyday life. It takes a sudden power failure to firmly indicate our dilemma. In the modern factory loss of power can result in stoppage of machinery, loss of time and costly damage. Many of the newer windowless plants depend on artificial light for their existence; thus, loss of light by power failure can cause accidents in addition to the foregoing results.

This work presents an exploration of autorotational behavior, observing naturally occurring structures to provide insight into the stability and design of autorotative mechanisms. A rotor is said to be in autorotation when, in the presence of airflow, a natural rotation generates lift to either suspend or slow the descent of a rotor. This phenomenon is observed in nature in the form of samaras, a seed pod morphology evolved in parallel by maple trees and many other organisms around the world. Simulation and experimental observation of samara vertical descent behavior provides insight into the stability of naturally evolved autorotative structures. A control-oriented model is presented to simulate the steady-state and dynamic behavior of single-winged samaras. The model is validated through experimentation and comparison to previous experimental data in the literature. This effort yields a compact model which allows for analytical exploration of design parameter bounds and stability. Autorotation provides a platform for development of unmanned aerial vehicles which can perform agile maneuvers and stable hovering in a power-efficient manner. The concept of tethered autogyros applies well to versatile surveillance platforms and high-altitude power generation; however, minimal prior literature exists on the tethered autogyro configuration. A generalized model is presented to explore the aerodynamic equilibrium space of autogyros in response to regenerative braking. Comparison with experimental data from the literature provides validation and visualizes the effects of varying inputs such as braking torque, wind speed, etc. This model is expanded to include the balancing forces of a catenary tether as well as the coupled aerodynamic and tether contributions within a wind field that varies with altitude in a physically accurate manner. Numerical methods are presented for solving aerodynamic equilibrium conditions and tether response coupling to explore the viability and practicality of high-altitude deployment for power generation as well as lower altitude extended and efficient flight of a smaller surveillance craft.

Most industrial manufacturing or processing plants use bolted connections between pipes that transfer media from one location to another. Gaskets are often used to seal these systems as they offer elevated levels of leak mitigation; however, despite their nearly universal usage, the current understanding of gasket mechanics at the meso-scale is still limited. Contemporary gaskets feature viscoelastic materials, fillers, textures, and are fabricated at various thicknesses. They are used in a wide range of thermal, mechanical, chemical, and temporal conditions. The current work characterizes polytetrafluoroethylene (PTFE) gaskets made with several different filler materials and having vastly different geometries. The chemically inert properties of this material and its relatively superior load retention properties make it appropriate for use in gaskets that are expected to retain load over hundreds of hours. As the degree to which certain factors influence gasket performance is still relatively unknown, several Analysis of Variance (ANOVA) studies are conducted to discover to what extent certain factors influence gasket load retention. Using a novel efficiency parameter (η) that compares experimental behavior to the behavior of an ideal gasket, these studies describe the impact of factors such as gasket texture, thickness, filler material, flange temperature, and the internal pressure of the flange. Additionally, component scale gasket behavior during service conditions is investigated via Finite Element Modeling. This model simulates the viscoelastic load retention behavior of these gaskets with a high degree of accuracy by using a Prony series approximation of Burger's model to characterize the viscoelastic properties of the material. A material database is used to verify and correct the model using experimental data. This collection contains data from gaskets of various textures, thicknesses and filler materials. Parameters for this model are obtained by using regression fits on a large number of data sets in the database and averaging the values of the parameters across the multiple tests. The collection of these research activities establishes a new framework that future engineers may use to characterize and even design new gaskets.

In the past several MRI compatible robotic needle guide devices for targeted prostate biopsy have been developed. The large and complex structure have been identified as the major limitations of those devices. Such limitations, in addition to complex steps for device to image registration have prevented widespread implementation of MRI-guided prostate biopsy despite the advantages of MRI compared to TRUS. We have designed a compact MRI-guided robotic intervention with the capability to have angulated insertion to avoid damage to any anatomical feature along the needle path. The system consists of a novel mechanism driven Robotic Needle Guide (RNG). The RNG is a 4-DOF robotic needle manipulator mounted on a Gross Positioning Module (GPM), which is locked on the MRI table. The RNG consists of four parallel stacked disks with an engraved profile path. The rotary motion and positioning of the discs at an angle aids in guiding the biopsy needle. Once a clinician selects a target for needle insertion, the intervention provides possible insertion angles. Then, the most suitable angle is selected by the clinician based on the safest trajectory. The selected target and insertion angle are then computed as control parameters of RNG i.e. the discs are then rotated to the required angle. Insertion is followed by quick confirmation scans to ascertain needle position at all times.

Monitoring intracranial pressure (ICP) is important for patients with increased intracranial pressure. Invasive methods of ICP monitoring include lumbar puncture manometry, which requires high precision, is costly, and can lead to complications. Non-invasive monitoring of ICP using tympanic membrane pulse (TMp) measurement can provide an alternative monitoring method that avoids such complications. In the current study, a piezo based sensor was designed, constructed and used to acquire TMp signals. The results showed that tympanic membrane waveform changed in morphology and amplitude with increased ICP, which was induced by changing subject position using a tilt table. In addition, the results suggest that TMp are affected by breathing, which has small effects on ICP. The newly developed piezo based brain stethoscope may be a way to monitor patients with increased intracranial pressure thus avoiding invasive ICP monitoring and reducing associated risk and cost.

Carbon nanopapers made of carbon nanotubes (CNTs) or carbon nanofibers (CNFs), possess unique electrical, thermal and mechanical properties and when integrated with a polymer matrix, can become a multifunctional composite capable of strain sensing and heat actuation. Smart structures such as these can be used in many applications including deployable space structures, human motion detection, and structural health monitoring as flexible, sensitive and stable strain sensors in addition to providing electrical heat actuation for the shape memory effect in polymers. This study focuses on strain sensing capabilities by developing a numerical model to predict piezoresistive behavior. The piezoresistive effect is a change in resistivity of a conductive network when a deformation is applied. This allows strain to be determined by simply measuring the electrical resistance. An equivalent resistor network can be formed to represent the fiber network. The proposed 2D model generates randomly oriented fibers inside a unit cell, determines their intersection points, and creates a mesh of the network for finite element analysis. Electrical conductivity is found for the initial and deformed fiber states by determining the current through the network for a known voltage. A piezoresistivity experimental study is conducted to investigate the strain sensing abilities of this material and validate model results. This simple model provides an initial framework that can be developed in future work. Despite its 2D nature, the model captures the governing mechanisms of piezoresistivity to a certain extent.

This thesis is about the design, development and integration of an in-situ compression stage which interfaces through the Leica optical microscope coupled with a Renishaw InVia micro-Raman spectrometer. This combined compression stage and Raman system will enable structural characterization of ceramics and ceramic composites. The in-situ compression stage incorporates a 440C stainless steel structural components, 6061 aluminum frame, a NEMA 23 stepper motor. Two load screws that allow to apply compressive loads up to 14,137 N, with negligible off axis loading, achieving target stresses of 500 MPa for samples of up to 6.00 mm in diameter. The system will be used in the future to study the structural changes in ceramics and ceramic composites, as well as to study thermal residual stress redistribution under applied compressive loads. A broad variety of Raman active ceramics, including the traditional structural ceramics 3mol%Y2O3-ZrO2, B4C, SiC, Si3N4, as well as exotic materials such as LaCoO3 and other perovskites will be studied using this system. Calibration of the systems load cell was performed in the configured state using MTS universal testing machines. To ensure residual stresses from mounting the load cell did not invalidate the original calibration, the in-situ compression stage was tested once attached to the Renishaw Raman spectrometer using LaCoO3 ceramic samples. The Raman shift of certain peaks in LaCoO3 was detected indicative of the effect of the applied compressive stress on the ceramics understudy.

Ball-and-plate balancing platforms have been utilized throughout academia to further understanding of nonlinearities that can occur when applying control algorithms to nonholonomic and underactuated systems. The objective of this thesis is to build upon an existing ball-and-plate balancing platform used in the Intro to Mechatronics class and create a robust platform system that can be utilized by future students to test various controller designs derived from MATLAB/Simulink®. The ball-and-plate platform design uses a myriad of sensors to track the system components in real time: a resistive touch panel is used to track the position of the ball on the plate, an inertial measurement unit is used to track the orientation of the top plate, and capacitive incremental encoders attached to the brushless-DC gimbal motors are used to both track the orientation of the motor actuation arms and commutate the motors. The gimbal motors are driven using the open-source ODrive motor driver, which receives torque commands from a separate STM32 microcontroller. The STM32 microcontroller aggregates and processes the data from the touch panel and IMU, and it acts as a “middle-man” for communication between the ODrive and MATLAB/Simulink® model running on a host PC. The platform successfully handles communications between the host PC, STM32, and ODrive at a rate of 200 Hz. The platform also incorporates a serial user interface that allows for fine position control of the motor arms for zeroing the top plate before each test.

The application of adaptive micro-electro-mechanical systems (MEMS) device in biologically-inspired cochlear model (cochlear biomodel) has been seen as a preferable approach to mimic closely the human cochlear response. The thesis focuses on the design and fabrication of resonant gate transistor (RGT) device applied towards the development of RGT cochlear biomodel. An array of RGT devices can mimic the cochlea by filtering the sound input signals into multiple electrical outputs. The RGT device consists of two main components; a) the MEMS bridge gate structure that transduces the sound input into mechanical vibrations and b) the channel with source/drain regions underneath the bridge gate structure that transduce the mechanical vibrations into electrical signals. The created mathematical model for RGT calculates the electrical outputs that are suited for neural spike coding. The neuromorphic auditory system is proposed by integrating the RGT devices with the spike event interface circuits. The novelty of the system lies in the adaptive characteristics of the RGT devices that can self-tune the frequency and sensitivity using the feedback control signals from the neuromorphic circuits. The bridge gates have been designed to cover the audible frequency range signals of 20 Hz - 20 kHz. Aluminium and tantalum have been studied as the material for the bridge gate structure. The fabrication of a bridge gate requires a gentle etch release technique to release the structure from a sacrificial layer. The downstream etch release technique employing oxygen/nitrogen plasma has been introduced and characterised. In the first iteration, aluminium bridge gates have been fabricated. The presence of tensile stress within aluminium had caused the aluminium bridge gates of length >1mm to collapse. In order to address this issue, tantalum bridge gates have been fabricated in the second iteration. Straight tantalum bridge gates in tensile stress and buckled tantalum bridge gates in compressive stress have been characterised. The frequency range of 550 Hz - 29.4 kHz has been achieved from the fabricated tantalum bridge gates of length 0.57mm - 5.8mm. The channel and source/drain regions have been fabricated and integrated with the aluminium or tantalum bridge gate structures to create the RGTs. In this study, the n-channel and p-channel resonant gate transistor (n-RGT and p-RGT) have been considered. In n-RGT, phosphorus ions are implanted to form the source/drain regions. High subthreshold currents have been measured from the n-RGTs. Thus, p- RGTs have been employed with considerably small subthreshold current. In p-RGT, boron ions are implanted to form the source/drain regions. The threshold voltage, transconductance and subthreshold current for both n-channel and p-channel resonant gate transistor devices have been characterised. In this work, the channel conductance of the n-RGT and p-RGT devices has been modulated successfully and the sensitivity tuning within the audible frequency range has been achieved from the tantalum bridge gates of the p-RGT devices. The characterisation and optimisation of the resonant gate transistor provide the first step towards the development of the adaptive RGT cochlear biomodel for the neuromorphic auditory system application.