Parabolic solar trough receivers are used to collect heat via the mean of a heat transfer fluid. This component is one among a myriad of the Concentrated Solar Power (CSP) devices. Parabolic troughs reach high temperatures around 400 ºC. improving the Parabolic Solar Trough's receiver with an IR selective coating will increase the heat transfer absorbed by the heat transfer fluid and reduce the radiative heat loss. Thus, optimizing the receiver will ameliorate the efficiency of the electrical production for a CSP. The parabolic solar receiver existing in industry currently are made of stainless steel with no specific coating for IR solar rays spectrum selection. Therefore, the heat transferred through the absorber is limited to certain light spectrum. Furthermore, numerous receivers proposed are made from materials that contaminates their optical properties when oxidized such as aluminum [1]. The heat transfer and optical analysis of the PTC are essential to optimize and understand its performance under high temperatures and reduce the heat loss. In this paper, our focus is on presenting a super-lattice IR selective coating to minimize the radiative heat loss. Making use of the power of metamaterials to confection optical properties that are inexistent in nature, the coating will serve to maximize the tube's reflectance above 70% in the IR. Not only does the selective coating enhance the optical properties of the receiver, but also it ensures performance stability for high temperatures.

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Mechanical metamaterials are becoming an emerging frontier in scientific research and engineering innovation due to its unique properties, arising from innovative geometrical designs rather than constituent materials. Reconfigurable metamaterials can change their shapes and structures dramatically under external forces or environmental stimuli. It offers an enhanced flexibility in performance by coupling dynamically changing structural configuration and tunable properties, which has found broad potential applications in 3D meso-structures assembly and programmable machines. Despite extensive studies on harnessing origami, the ancient paper folding art, for design of mechanical metamaterials, the study on utilizing its close cousin, kirigami (“kiri” means cut), for programmable reconfigurable mechanical metamaterials and machines remains largely unexplored. In this dissertation, I explore harnessing the uniqueness of cuts in kirigami for achieving extraordinary mechanical properties and multifunctionalities in krigami-based metamaterials, as well as its potential applications in programmable machines and soft robotics. I first exploit the design of hierarchical cuts for achieving high strength, high stretchability, and tunable mechanical properties in hierarchical rotation-based kirigami mechanical metamaterials. Hierarchical line cuts are introduced to a thin sheet composed of non-stretchable materials (copy paper), less stretchable materials (acrylics), and highly stretchable materials (silicone rubber, PDMS), to explore the role of constituent material properties. The cut unit in the shape of solid rectangles with the square shape as a special case was demonstrated for achieving the extreme stretchability via rigid rotation of cut units. It shows that a higher hierarchical level contributes to a higher expandability and lower stiffness to constituent material. However, when such kirigami structure is applied onto less-stretchable materials (e.g. acrylics), its stretchability is almost eliminated regardless of the hierarchical level, because severe stress concentration at rotation hinges leads to the structure failure at the very beginning stage of pattern transformation. To address this challenge, I propose a hinge design which can significantly reduce the stress concentration at cut tips and enable high stretchability for rotation-based kirigmai structure, even on acrylic thin sheet. I also study the tunable photonic behavior of proposed hierarchical kirigami metamaterial by simple strain-induced structural reconfiguration. I then explore the programmability of kiri-kirgami structures by introducing notches to the simplest kirigami structure patterned with parallel line cuts for breaking its deformation symmetry. Engraving the flat-cut kirigami structure enables programmable control of its out-of-plane tilting orientation, thus generating a variety of inhomogeneous structural configurations on demand. I find that compared to the its counterpart without engraving notches, the introduced notches have a negligible effect on both the stress-strain curve over the large strain range and the extreme stretchability, however, they reduce the critical buckling force largely. Furthermore, I demonstrate the adaptive kiri-kirigami structure through local actuation with its tilting directions to be programmed and switched in response to the change of environmental temperature. Lastly, I demonstrate the potential promising outcome of kiri-kirigami structures as adaptive building envelope in energy efficient buildings, especially in electric saving for lighting and cooling load saving through numerical simulation. In addition to kirigami based soft metamaterials, I also investigate the utilization of soft materials and soft structures for robotics functions. First, I explore the design of soft doming actuator upon pneumatic actuation and its implications in design of multifunctional soft machines. I propose a novel bilayer actuator, which is composed of patterned embedded pneumatic channel on top for radial expansion and a solid elastomeric layer on bottom for strain-limiting. I show that both the cavity volume and bending angle at the rim of the actuated dome can be controlled by tuning the height gradient of the pneumatic channel along the radial direction. I demonstrate its potential multifunctional applications in swimming, adhesion, and gripping. I further explore harnessing doming-based bilayer doming actuator for developing soft climbing robot. I characterize and optimize the maximum shear adhesion force of the proposed soft adhesion actuator for strong and rapid reversible adhesion on multiple types of smooth and semi-smooth surfaces. Based on the switchable adhesion actuator, I design and fabricate a novel load-carrying amphibious climbing soft robot (ACSR) by combining with a soft bending actuator. I demonstrate that it can operate on a wide range of foreign horizontal and vertical surfaces, including dry, wet, slippery, smooth, and semi-smooth ones on ground, as well as under water with certain load-carrying capability. I show that the vertical climbing speed can reach about 286 mm/min (1.6 body length/min) while carrying over 200g object (over 5 times the weight of ACSR itself) during climbing on ground and under water. / Mechanical Engineering

Yes / This paper presents empirical results of an innovative beam scanning leaky-wave antenna (LWA) which enables scanning over a wide angle from -35o to +34.5o between 57 GHz and 62 GHz, with broadside radiation centered at 60 GHz. The proposed LWA design is based on composite right/left-handed transmission-line (CRLH-TL) concept. The single layer antenna structure includes a matrix of 3×9 square slots that is printed on top of the dielectric substrate; and printed on the bottom ground-plane are Π and Tshaped slots that enhance the impedance bandwidth and radiation properties of the antenna. The proposed antenna structure exhibits metamaterial property. The slot matrix provides beam scanning as a function of frequency. Physical and electrical size of the antenna is 18.7×6×1.6 mm3 and 3.43􀣅􀫙×1.1􀣅􀫙×0.29􀣅􀫙, respectively; where 􀣅􀫙 is free space wavelength at 55 GHz. The antenna has a measured impedance bandwidth of 10 GHz (55 GHz to 65 GHz) or fractional bandwidth of 16.7%. Its optimum gain and efficiency are 7.8 dBi and 84.2% at 62 GHz. / Partially supported by innovation programme under grant agreement H2020-MSCA-ITN-2016 SECRET- 722424 and the financial support from the UK Engineering and Physical Sciences Research Council (EPSRC) under grant EP/E022936/1.

After being theorized by Veselago in 1967, recent developments in metamaterials over the last two decades have allowed scientists and researchers to physically demonstrate that artificial composite media can be engineered to exhibit exotic material properties, such as negative refractive index, by exploiting features in arrays of sub-wavelength unit inclusions. These unconventional electromagnetic properties are realized through the coupling of the microscopic unit inclusions, which govern the macroscopic properties of the structure. After demonstrating that a periodic array of capacitively-loaded loop (CLL) inclusions paired with continuous wire results in negative refraction, this study performs numerical simulations to characterize random metamaterial structures. These structures consist of CLLs that are randomized in both position and orientation. In addition, this thesis introduces an innovative antenna enhancing structure consisting of capacitively-loaded loop (CLL) metamaterial elements loaded radially around a standard dipole antenna at an electrically small distance. As a result of this innovative arrangement, the dipole antenna is easily transformed into a directive mechanically scanned antenna with high realized gain. The desired directivity and gain can be tuned based on the number of radial CLL fins placed around the dipole. Interactions between the antenna and metamaterial elements result in significant enhancement of the maximum radiated field amplitude and front-to-back ratio. This innovative CLL-loaded dipole antenna is compared to the conventional Yagi-Uda antenna. The structures presented in this thesis are modeled using full-wave simulation, and one antenna structure is experimentally verified as a proof-of-concept. / Master of Science

Focused ultrasound (FUS) is an emerging technology, and it plays an essential role in clinical and contactless acoustic energy transfer applications. These applications have critical criteria for the acoustic pressure level, the creation of complex pressure patterns, spatial management of the complicated acoustic field, and the degree of nonlinear waveform distortion at the focal areas, which have not been met to date. This dissertation focuses on introducing experimentally validated novel numerical approaches, optimization algorithms, and experimental techniques to fill existing knowledge gaps and enhance the functionality of holographic acoustic lenses (HALs) with an emphasis on applications related to biomedical-focused ultrasound and ultrasonic energy transfer. This dissertation also aims to investigate the dynamics of nonlinear acoustic beam shaping in engineered HALs. First, We will introduce 3D-printed metallic acoustic holographic mirrors for precise spatial manipulation of reflected ultrasonic waves. Optimization algorithms and experimental validations are presented for applications like contactless acoustic energy transfer. Furthermore, a portion of the present work focuses on designing holographic lenses in strongly heterogeneous media for ultrasound focusing and skull aberration compensation in transcranial-focused ultrasound. To this end, we collaborated with the Biomedical Engineering and Mechanics Department as well as Fralin Biomedical Research Institute to implement acoustic lenses in transcranial neuromodulation, targeting to improve the quality of life for patients with brain disease by minimizing the treatment time and optimizing the ultrasonic energy into the region of interest. We will also delve into the nonlinear regime for High-Intensity Focused Ultrasound (HIFU) applications, this study is structured under three objectives: (1) establishing nonlinear acoustic-elastodynamics models to represent the dynamics of holographic lenses under low- to high-intensity acoustic fields; (2) validating and leveraging the resulting models for high-fidelity lens designs used in generating specified nonlinear ultrasonic fields of complex spatial distribution; (3) exploiting new physical phenomena in acoustic holography. The performed research in this dissertation yields experimentally proven mathematical frameworks for extending the functionality of holographic lenses, especially in transcranial-focused ultrasound and nonlinear wavefront shaping, advancing knowledge in the burgeoning field of the inverse issue of nonlinear acoustics, which has remained underdeveloped for many years. / Doctor of Philosophy / Ultrasonic waves are sound waves that have frequencies higher than the upper audible limit of human hearing. The versatility and non-invasive nature of ultrasonic waves make them a valuable tool in numerous scientific, medical, and industrial applications. In healthcare, ultrasonic waves are employed in diagnostic imaging techniques, such as ultrasound scans, to create images of internal body structures. Ultrasonic waves are also used for non-destructive testing (NDT) of materials, detecting flaws or cracks within structures without causing any damage. Furthermore, this technology finds applications in the field of material science for the manipulation of particles and in biomedical research for drug delivery systems. Focused ultrasound sound is an emerging non-invasive therapeutic modality that uses focused ultrasound waves to target tissue within the body without damaging the surrounding tissue. This technology allows for precise delivery of ultrasound energy to a specific region, where it can induce various desired therapeutic effects depending on the targeting location and parameters. Therapeutic focused ultrasound has the advantage of being non-invasive, reducing the risks and recovery time associated with traditional surgery. It can be precisely controlled and monitored in real-time with imaging techniques such as ultrasound or MRI, ensuring the targeted treatment of pathological tissues while sparing healthy ones. Applications of therapeutic are broad and include tumor ablation, facilitation of drug delivery across the blood-brain barrier, relief of chronic pain, and treatment of essential tremor and other neurological disorders. The domain of therapeutic focused ultrasound is continually advancing, driven by research that seeks to extend its applications. Recent developments in acoustic engineering and 3D printing have led to the creation of acoustic holograms, or holographic acoustic lenses, which allow for more refined control over the spatial structure of the acoustic field. These technological advancements hold the promise of enhancing FUS by improving the accuracy of acoustic field localization and providing a more cost-effective solution compared to conventional systems like phased array transducers. However, the accuracy and applicability of existing models and techniques are constrained by assumptions, including the uniformity of the propagation medium and the linearity of the acoustic field, which limits the functionality and restricts the potential applications of acoustic holograms. In this dissertation, we present novel numerical techniques, algorithms, and proof-of-concept experiments to fill those knowledge gaps and expand the functionality of acoustic holograms in crucial applications.

Mechanical metamaterials are novel materials that display unique properties from their underlying microstructure topology rather than the constituent material they are made from. Their effective properties displayed at macroscale depend on the design of their microstructural topology. In this work, two classes of mechanical metamaterials are studied within the 2D-space. The first class is made of trusses, referred to as truss-based mechanical metamaterials. These materials are studied through their application to a beam component, where finite element analysis is performed to determine how truss-based microstructures affect the displacement behavior of the beam. This analysis is further subsidized with the development of a graphical user interface, where users can design a beam made of truss-based microstructures to see how their design affects the beam's behavior. The second class of mechanical metamaterial investigated is made of self-assembled structures, called spinodoids. Their smooth topology makes them less prone to high stress concentrations present in truss-based mechanical metamaterials. A large database of spinodoids is generated in this study. Through data-driven modeling the geometry of the spinodoids is coupled with their Young's modulus value to approach inverse design under uncertainty. To see mechanical metamaterials applied to industry they need to be better understood and thoroughly characterized. Furthermore, more tools that specifically help push the ease in the design of these metamaterials are needed. This work aims to improve the understanding of mechanical metamaterials and develop efficient computational design strategies catered solely for them. / Master of Science / Mechanical metamaterials are hierarchical materials involving periodically or aperiodically repeating unit cell arrangements in the microscale. The design of the unit cells allows these materials to display unique properties that are not usually found in traditionally manufactured materials. This will enable their use in a multitude of potential engineering applications. The presented study seeks to explore two classes of mechanical metamaterials within the 2D-space, including truss-based architectures and spinodoids. Truss-based mechanical metamaterials are made of trusses arranged in a lattice-like framework, where spinodoids are unit cells that contain smooth structures resulting from mimicking the two phases that coexist in a phase separation process called spinodal decomposition. In this research, computational design strategies are applied to efficiently model and further understand these sub-classes of mechanical metamaterials.

4D printing is a rapidly emerging field in which 3D printed stimuli-responsive materials produce morphing and multifunctional structures, with time being the fourth dimension. This approach enables the 3D printing of pre-programmed responsive sheets, which transition into complex curved shapes upon exposure to external stimuli, resulting in a substantial reduction in material consumption and printing time (70 - 90 %). Commonly used materials for 4D printing are polymer composites, such as hydrogels, polydimethylsiloxane (PDMS), liquid crystal elastomers (LCEs), and shape memory polymers (SMPs). However, the low elastic modulus (E) that these materials exhibit during shape change (E range of 10-4 – 10 MPa) limits their scalability, actuation stress, and load bearing. Moreover, these materials exhibit low ultimate stresses, leading to correspondingly low toughness (K) values in the range of 0.08 to 5 MJ m-3. Consequently, this results in structures with low damage tolerance. Therefore, an existing challenge for the field of 4D printing is to develop materials that can maintain their large and predictable morphing mechanism for complex shape transformation, while improving the E and K for high performance applications. Furthermore, many existing approaches rely on passive structures that necessitate the control of global conditions of the surrounding environment (e.g., hot plates, ovens, external magnets, water baths) to provide the stimulus for actuation. In this work, we tackle these challenges by introducing novel materials, ink formulations, and innovative printing techniques for multi-material Direct Ink Writing (DIW). We aim to create electrically controllable 4D printed structures that exhibit exceptional stiffness and toughness, all while preserving a large and predictable morphing mechanism for intricate shape transformations. First, we introduce multiscale heterogeneous polymer composites as a novel category of stiff, electrically controllable thermally responsive 4D printed materials. These composites consist of an epoxy matrix with an adjustable cross-link density and a plurality of isotropic and anisotropic nanoscale and microscale fillers. Leveraging this platform, we generate a set of 37 inks covering a broad range of negative and positive linear coefficients of thermal expansion. This set of inks exhibits an elastic modulus range that is four orders of magnitude greater than that of existing 4D printed materials and offers tunable electrical conductivities for simultaneous Joule heating actuation and self-sensing capabilities. Utilizing electrically controllable bilayers as building blocks, we design and print a flat geometry that changes shape into a 3D self-standing lifting robot, displaying record actuation stress and specific force when compared to other 3D printed actuators. We integrate this lifting robot with a closed-loop control system, achieving autoregulated actuation exhibiting a 4.8 % overshoot and 0.8 % undershoot, while effectively rejecting disturbances of up to 170 times the robot's weight. Furthermore, we employ our ink palette to create and 3D print planar lattice structures that transform into various self-supporting complex 3D surfaces. Ultimately, we achieve a 4D printed electrically controlled crawling robotic lattice structure, highlighting its capacity to transport loads up to 144 times its own weight. Finally, we introduced a printable PDMS adhesive that serves as synthetic fascia to hold our epoxy-based synthetic muscle together, enhancing the K of our 4D printed structures, all while maintaining high stiffness, large, predictable, and addressable actuation mechanism. Through the integration of these soft adhesive materials with high-stiffness thermally responsive epoxies via DIW, we achieved an improvement of about two orders of magnitude in the K of the resulting synthetic muscle composite, all while maintaining high stiffness and morphing mechanism. Utilizing this fabrication method, we printed an electrically controllable bilayer exhibiting damage detection and tolerance, enduring up to 7 fractures while continuing to function effectively. Furthermore, we integrated the synthetic muscle composite into our lifting robot design, setting yet again new records in specific force and actuation stress when compared to other 3D printed actuators. Notably, even after failure, the actuator maintained its operational integrity and high performance. Ultimately, we present a 4D printed lattice structure featuring the incorporation the synthetic muscle composite, showcasing a sensitive electrically responsive surface with fracture detection capabilities. To emphasize this, we subjected one of these 4D printed lattices to extreme conditions, driving a car over it. Notably, the lattice structure detected fractures and exhibited high resilience, enduring external compressive damage equivalent to 331,060 times its own weight. / 2026-05-23T00:00:00Z