Drawing from the lessons of plant transpiration, this dissertation explores a biomimiced system for fluid transport and thermal regulation. This system utilizes evaporation and benefits from the associated passive pumping with an application of a rooftop solar radiation barrier in mind. By directing the incoming energy towards the phase change of water, lower surface temperatures can be maintained thus reducing heat transfer into the structure by conduction. In order to design and construct such a bio-inspired system, several parameters, i.e., the evaporation surface, the delivery path and the working fluid, must be understood as to how they affect and limit operations. Performance factors such as evaporation rate and suction pressure were monitored for the various design constraints of feeding tube length and diameter, membrane area, and working fluid. Additionally, as a heat flux was imposed on the membrane from above and below, the substrate temperature became important. Over the range of parameters tested, hydrodynamic resistances of the delivery path were shown to affect pumping height but not the evaporation rate. Instead, the evaporation rate was controlled by the substrate temperature. Furthermore, the normalized evaporation rate was found to be inversely related to the evaporation surface area. Under contaminated working fluid conditions, particles deposited in the membrane caused decreases in evaporation rates. When applied to a simulated roof situation, the evaporation system was successful at maintaining considerably lower surface temperatures than other conventional and unconventional roof albedos, which, in turn, would reduce heat flux into the interior by conduction. Lastly, in estimating the water consumption, on a typical August day in Austin, TX, the system could use up to 2 gallons/m² while providing enhanced cooling. When the system's resources were compared to being purposed in other ways, they were arguably better utilized in providing evaporative cooling. / text

The remarkable attachment system of geckos has inspired the development of dry microfiber adhesives through the last two decades. Some of the notable characteristics of gecko-inspired fibrillar adhesives include: strong, directional, and controllable adhesion to smooth and rough surfaces in air, vacuum, and under water; ability to maintain strong adhesion during repeated use; anti-fouling and self-cleaning after contamination. Given these outstanding qualities, fibrillar adhesives promise an extensive range of use in industrial, robotic, manufacturing, medical, and consumer products. Significant advancements have been made in the design of geckoinspired microfiber adhesives with the characteristic properties listed above, with the exception of the anti-fouling and self-cleaning features. The self-cleaning mechanism of the gecko’s adhesion system plays an important role to its ability to remain sticky in various environments. Similarly, enabling self-cleaning capability for synthetic microfiber adhesives will lead to robust performance in various areas of application. Presently, the practical use of fibrillar adhesives is restricted mainly to clean environments, where they are free from contaminants. The goal of this thesis is to conduct a detailed study of the mechanisms and mechanics of contact-based self-cleaning of gecko-inspired microfiber adhesives. This work focuses on contact self-cleaning mechanisms, as a more practical approach to cleaning. Previous studies on the cleaning of microfiber adhesives have mostly focused on mechanisms that involve complete removal of the contaminants from the adhesive. In this thesis, a second cleaning process is proposed whereby particles are removed from the tip of the microfibers and embedded between adjacent microfibers or in grooves patterned onto the adhesive, where they are no longer detrimental to the performance of the adhesive. In this work, a model of adhesion for microfiber adhesives that take the deformation of the backing layer under individual microfiber is developed. The dependence of adhesion of microfiber adhesives on the rate of unloading is also modeled and verified using experiments. The models of adhesion presented are later used to study the mechanics of contact self-cleaning of microfiber adhesives. Three major categories of self-cleaning are identified as wet self-cleaning, dynamic self-cleaning, and contact self-cleaning. A total of seven self-cleaning mechanisms that are associated with these categories are also presented and discussed. Results from the self-cleaning model and experiments show that shear loading plays an important role in self-cleaning. The underlying mechanism of contact self-cleaning due to normal and shear loading for spherical contaminants is found to be the particle rolling between the adhesive and a contacted substrate. Results from the model and experiments also show that small microfiber tips (much less than the size of the contaminants) are favorable for self-cleaning. On the other hand, large microfiber tips (much larger than the size of the contaminants) are favorable for anti-fouling of the microfiber adhesive. Results from this work suggests that the sub-micrometer size of the gecko’s adhesive fibers and the lamellae under the gecko toes contribute to its outstanding self-cleaning performance. The results presented in this thesis can be implemented in the design of microfiber adhesives with robust adhesion, self-cleaning and anti-fouling characteristic, for use in numerous applications and in various environments.

A Systematic Approach to Bio-inspired Conceptual Design

abstract: Development of efficient and renewable electrocatalytic systems is foundational to creation of effective means to produce solar fuels. Many redox enzymes are functional electrocatalysts when immobilized on an electrode, but long-term stability of isolated proteins limits use in applications. Thus there is interest in developing bio-inspired functional catalysts or electrocatalytic systems based on living organisms. This dissertation describes efforts to create both synthetic and biological electrochemical systems for electrocatalytic hydrogen production. The first part of this dissertation describes the preparation of three different types of proton reduction catalysts. First, four bioinspired diiron complexes of the form (μ-SRS)Fe(CO)3[Fe(CO)(N-N)] for SRS = 1,2-benzenedithiolate (bdt) and 1,3-propanedithiolate (pdt) and N-N = 2,2’-bipyridine (bpy) and 2,2’-bypyrimidine (bpym), are described. Electrocatatlytic experiments show that although the byprimidinal complexes are not catalysts, the bipyridyl complexes produce hydrogen from acetic acid under reducing conditions. Second, three new mononuclear FeII carbonyl complexes of the form [Fe(CO)(bdt)(PPh2)2] in which P2 = bis-phosphine: 4,5-Bis(diphenylphosphino)- 9,9-dimethylxanthene (Xantphos), 1,2-Bis(diphenylphosphino)benzene (dppb), or cis- 1,2-Bis(diphenylphosphino)ethylene (dppv) are described. All are functional bio-inspired models of the distal Fe site of [FeFe]-hydrogenases. Of these, the Xanthphos complex is the most stable to redox reactions and active as an electrocatalyst. Third, a molybdenum catalyst based on the redox non-innocent PDI ligand framework is also shown to produce hydrogen in the presence of acid. The second part of this dissertation describes creating functional interfaces between chemical and biological models at electrode surfaces to create electroactive systems. First, covalent tethering of the redox probe ferrocene to thiol-functionalized reduced graphene oxide is demonstrated. I demonstrate that this attachment is via the thiol functional groups. Second, I demonstrate the ability to use electricity in combination with light to drive production of hydrogen by the anaerobic, phototrophic microorganism Heliobacterium modesticaldum. / Dissertation/Thesis / Doctoral Dissertation Biochemistry 2017

abstract: Existing robotic excavation research has been primarily focused on lunar mining missions or simple traffic control in confined tunnels, however little work attempts to bring collective excavation into the realm of human infrastructure. This thesis explores a decentralized approach to excavation processes, where traffic laws are borrowed from swarms of fire ants (Solenopsis invicta) or termites (Coptotermes formosanus) to create decision rules for a swarm of robots working together and organizing effectively to create a desired final excavated pattern. First, a literature review of the behavioral rules of different types of insect colonies and the resulting structural patterns over the course of excavation was conducted. After identifying pertinent excavation laws, three different finite state machines were generated that relate to construction, search and rescue operations, and extraterrestrial exploration. After analyzing these finite state machines, it became apparent that they all shared a common controller. Then, agent-based NetLogo software was used to simulate a swarm of agents that run this controller, and a model for excavating behaviors and patterns was fit to the simulation data. This model predicts the tunnel shapes formed in the simulation as a function of the swarm size and a time delay, called the critical waiting period, in one of the state transitions. Thus, by controlling the individual agents' behavior, it was possible to control the structural outcomes of collective excavation in simulation. To create an experimental testbed that could be used to physically implement the controller, a small foldable robotic platform was developed, and it's capabilities were tested in granular media. In order to characterize the granular media, force experiments were conducted and parameters were measured for resistive forces during an excavation cycle. The final experiment verified the robot's ability to engage in excavation and deposition, and to determine whether or not to begin the critical waiting period. This testbed can be expanded with multiple robots to conduct small-scale experiments on collective excavation, such as further exploring the effects of the critical waiting period on the resulting excavation pattern. In addition, investigating other factors like tuning digging efficiency or deposition proximity could help to transition the proposed bio-inspired swarm excavation controllers to implementation in real-world applications. / Dissertation/Thesis / Masters Thesis Mechanical Engineering 2018

abstract: Honeycomb sandwich panels have been used in structural applications for several decades in various industries. While these panels are lightweight and rigid, their design has not evolved much due to constraints imposed by available manufacturing processes and remain primarily two-dimensional extrusions sandwiched between facings. With the growth in Additive Manufacturing, more complex geometries can now be produced, and advanced design techniques can be implemented into end use parts to obtain further reductions in weight, as well as enable greater multi-functionality. The question therefore is: how best to revisit the design of these honeycomb panels to obtain these benefits? In this work, a Bio-Inspired Design approach was taken to answer this question, primarily since the hexagonal lattice is so commonly found in wasp and bee nests, including the well-known bee’s honeycomb that inspired these panel designs to begin with. Whereas prior honeycomb panel design has primarily focused on the hexagonal shape of the unit cell, in this work we examine the relationship between the various parameters constituting the hexagonal cell itself, specifically the wall thickness and the corner radius, and also examine out-of-plane features that have not been previously translated into panel design. This work reports findings from a study of insect nests across 70 species using 2D and 3D measurements with optical microscopy and X-ray tomography, respectively. Data from these biological nests were used to identify design parameters of interest, which were then translated into design principles. These design principles were implemented in the design of honeycomb panels manufactured with the Selective Laser Sintering process and subjected to experimental testing to study their effects on the mechanical behavior of these panels. / Dissertation/Thesis / Masters Thesis Manufacturing Engineering 2020

In recent years, the field of Soft Robotics has grown exponentially resulting in a variety of different soft robot designs. A majority of the current soft robots can easily be split into two distinct categories: Navigation and Grasping. Navigation robots alter their body orientation to navigate around an environment. Grasping robots are designed to grasp a variety of unknown objects without damaging said object. However, only a few robots are able to demonstrate both aspects and even fewer robots are able to do both simultaneously. As thus, the goal of this thesis is to create a soft robot that is able to pick up and support an additional payload. This thesis will explore the challenges and difficulties that come with designing such a robot. For this thesis, we chose to simplify the manufacturing process making it easy to create and test different designs. We primarily used Pneumatic Network actuators for the majority of the soft robot. This allowed us to use a layered manufacturing approach to create the full robot. Finally, we split the robot into two main components which have their own purpose, which made it easy to test and design each component. Attached to this thesis are three different supplementary videos. The first one labeled "Walking Gaits" demonstrate how the robot is capable of moving forward. This video is comprised of several sections showing the full robot moving, just the base moving, and the full robot briefly moving as it supports a payload. The second video is labeled "Additional Walking". This video shows how the base can effectively move around a given environment. The final video if called "Grasping Method" which demonstrates the different grasping methods that the full robot uses to pick up objects. / 2021-06-03T00:00:00Z

<p>Insects and hummingbirds not only can perform long-term stationary hovering but also are capable of acrobatic maneuvers. At their body scale, such extraordinary flight performance remains unmatched by state-of-the-art conventional man-made aerial vehicles with fixed or rotary wings. Insects' and hummingbirds' near maximal performance come from their highly intricate and powerful wing-thorax actuation systems, sophisticated sensory system, and precise neuromotor control. Flapping Wing Micro Air Vehicles (FWMAVs) with bio-inspired flapping flight mechanisms hold great promise in matching the performance gap of their natural counterparts. Developing such autonomous flapping-wing vehicles to achieve animal-like flight, however, is challenging. The difficulties are mainly from the high power density requirements under the stringent constraints of scale, weight, and power, severe system oscillations induced by high-frequency wing motion, high nonlinearity of the system, and lack of miniature navigation sensors, which impede actuation system design, onboard sensing, flight control, and autonomous navigation. </p><p><br></p><p>To address these open issues, in this thesis, we first introduce systematic modeling of a dual-motor hummingbird-scale flapping wing robot. Based upon it, we then present studies of the onboard sensor fusion, flight control, and navigation method. </p><p><br></p><p>By taking the key inspiration from its natural counterparts, the proposed hummingbird robot has a pair of independently controlled wings. Each wing is directly actuated by a dc motor. Motors undergo reciprocating motion. Such a design is a severely underactuated system, namely, it relies on only two actuators (one per wing) to control full six degrees of freedom body motion. As a bio-inspired design, it also requires the vehicle close to its natural counterparts’ size and weight meanwhile provide sufficient lift and control effort for autonomy. Due to stringent payload limitation from severe underactuation and power efficiency challenges caused by motor reciprocating motion, the design and integration of such a system is a challenging task. In this thesis, we present the detailed modeling, optimization, and system integration of onboard power, actuation, sensing, and flight control to address these unique challenges. As a result, we successfully prototyped such dual-motor powered hummingbird robot, either with power tethers or fully untethered. The tethered platform is used for designing onboard sensing, control, and navigation algorithms. Untethered design tackles system optimization and integration challenges. Both tethered/untethered versions demonstrate sustained stable flight. </p><p><br></p><p>For onboard attitude sensing, a real-time sensor fusion algorithm is proposed with model-based adaptive compensation for both sensor reading drift and wing motion induced severe system vibration. With accurate and robust sensing results, a nonlinear robust control law is designed to stabilize the system during flight. Stable hovering and waypoint tracking flight were experimentally conducted to demonstrate the control performance. In order to achieve natural flyers' acrobatic maneuverability, we propose a hybrid control scheme by combining a model-based robust controller with a model-free reinforcement learning maneuver policy to perform aggressive maneuvers. The model-based control is responsible for stabilizing the robot in nominal flight scenarios. The reinforcement learning policy pushes the flight envelope to pilot fierce maneuvers. To demonstrate the effectiveness of the proposed control method, we experimentally show animal-like tight flip maneuver on the proposed hummingbird robot, which is actuated by only two DC motors. These successful results show the promise of such a hybrid control design on severely underactuated systems to achieve high-performance flight.</p><p><br></p><p>In order to navigate confined space while matching the design constraints of such a small robot, we propose to use its wings in dual functions - combining sensing and actuation in one element, which is inspired by animals' multifunctional flapping wings. Based on the interpretation of the motor current feedback which directly indicates wing load changes, the onboard somatosensory-like feedback has been achieved on our hummingbird robot. For navigation purposes, such a method can sense the presence of environmental changes, including grounds, walls, stairs, and obstacles, without the need for any other sensory cues. As long as the robot can fly, it can sense surroundings. To demonstrate this capability, three challenging tasks have been conducted onto the proposed hummingbird robot: terrain following, wall detection and bypass, and navigating a confined corridor. </p><p><br></p><p>Finally, we integrate the proposed methods into the untethered platform, which enables stable untethered flight of such a design in both indoor and outdoor tests. To the best of our knowledge, this result presents the first bio-inspired FWMAV powered by only two actuators and capable of performing sustained stable flight in both indoor and outdoor environment. It is also the first untethered flight of an at-scale tailless hummingbird robot with independently controlled wings, a key inspiration from its natural counterparts.</p><div><div><div><div><div> </div> </div> </div></div></div>

Acoustic-structural interaction is the key to understand a wide range of engineering problems such as membrane-based dynamic pressure sensors, hearing devices for sound source localization, and acoustic absorbers for noise reduction. Despite tremendous developments in the last decades, there is still a fundamental size limitation in these areas. In the case of dynamic pressure sensors, sensitivity usually suffers for miniature sensors; the available acoustic directional cues proportionally decrease with size, which adversely affects the localization performance; thick panels are required to achieve superior sound attenuation, particularly for low-frequency sound. It is the motivation of this dissertation research to address the abovementioned size limitation that involves acoustic-structural interaction. The overall goal of this dissertation work is to achieve an enhanced understanding of the acoustic-structural interaction between diaphragms and air cavity and to apply this understanding to develop high-performance miniature acoustic sensors and noise reduction metamaterials. First, a finite element method (FEM) model and large-scale device are developed to understand how the interaction between the diaphragm and its backing air cavity affects the equivalent mass, stiffness, and damping of air-backed diaphragms. The numerical and experimental study shows that the complex interaction cannot be captured by the commonly used lump model. Then, air-backed graphene diaphragms are used to develop fiber optic sensors with sub-millimeters footprint and high sensitivity. Two different configurations are designed to enhance the sensor sensitivity limited by the backing air cavity. One is to increase the mechanical sensitivity by using a larger backing volume, the other is to increase the optical sensitivity by using silver-graphene composite diaphragm. Next, acoustic metamaterials with air-coupled diaphragms as unit cells are developed to achieve perfect acoustic absorption with thickness much smaller than the sound wavelength, which cannot be realized using natural materials. Finally, an expanded configuration of two diaphragms coupled by an air-filled tunnel is experimentally developed to mimic the hearing system of small vertebrates. The goal is to amplify the small directional cues available to the small animals so that a high angular resolution can be achieved. This dissertation provides a quantitative and mechanistic explanation for the interaction between the diaphragms and the sealed air cavity. It offers several frameworks for the development of miniature pressures, directional sensors, and thin sound absorbers. / Mechanical Engineering

Male cicada’s superior sound producing ability has been well studied by entomologists and ethologists. The secret behind the loud sound is the dual-resonator structure: the primary resonator is a series of buckled ribs/beams on its tymbal organ, while the secondary resonator is a large air cavity in the abdomen with a pair of openings. However, the understanding of the dual-resonator structure is incomplete, and few endeavors have been reported on developing cicada-inspired novel acoustic devices. To this end, this dissertation research aims to achieve a fundamental understanding of the cicada-inspired sound generating structures, and to apply the knowledge to develop a dual-resonator system with superior sound generating ability.First, a clamped-clamped buckled beam – the fundamental vibration source of the dual-resonator system – is modeled and tested for free vibration responses during the snap-through process between its bistable positions. It is found that the free vibration of the buckled beam is independent from actuation. In terms of the natural frequencies and the vibrational mode shapes, the free vibration is determined only by the geometry and material properties of the buckling beam. The experiment provides a comprehensive insight of the snap-through process and the induced free vibrations. Second, both analytical and experimental methods are used to investigate the buckling beam from an energy perspective, including the force needed for actuating the buckled beam, the work by the actuation force, the elastic energy of the buckling beam, and the sound radiation characteristics. Results show that although the actuation forces depend on its acting locations, the work by the force remains constant, which is equal to the elastic energy difference between the first symmetric buckling mode and the first anti-symmetric buckling mode. Acoustic analysis shows that the sound radiation is mostly generated from the first symmetric vibrational mode. Third, the dual-resonator system consisting of a buckling beam and a Helmholtz resonator is proposed. Considered as an equivalent two-degree-of-freedom vibration system, the dual-resonator system is modeled and studied for optimal sound output. Finally, a dual-resonator system is fabricated with the optimal parameters. Experimental characterization shows superior sound outputs of the dual-resonator system similar to what are observed in male cicadas. This dissertation sheds new lights on the structural-acoustic interaction of buckling beam and Helmholtz resonator that is found in the sound-producing organs of male cicadas and develops a cicada-inspired dual-resonator system for the first time. Findings from this research not only enhance the existing knowledge on male cicadas, but also pave the way for its engineering applications that require highly efficient sound radiation. / Mechanical Engineering