This PDF file contains the front matter associated with SPIE Proceedings Volume 11588, including the Title Page, Copyright information, and Table of Contents.

All around us our world is undergoing rapid transformative change, from energy to mobility to manufacturing. To meet volatile needs, there is a growing demand for integrative thinking. Integrative thinking is systematically integrating disparate disciplines to effectively tackle complex engineering problems. For decades, the field of Smart Materials and Structures has fostered an integrative mindset – it is in our DNA. Yet, while our field has made great strides in research, successful transition and adoption of technology in the field still tends to be a challenge. Highlighting several integrative smart systems from the past to the future, this talk is designed to provoke a conversation within the community with the hopes to inspire the advocacy of our integrative thinking beyond our field to empower solutions to the most pressing problems of today.

This talk will cover select examples and highlights from our recent and ongoing efforts on the dynamics of piezoelectric structures and systems, ranging from nonlinear energy harvesting and bio-inspired aquatic locomotion to elastic wave guiding and vibration attenuation via programmable metamaterials, and most recently wireless power and data transfer, as well as biomechanical applications. First, we will discuss the use of piezoelectric materials in conjunction with various nonlinear structures for frequency bandwidth enhancement in vibration energy harvesting. Inherent piezoelectric nonlinearities and their interaction with designed geometric nonlinearities will also be briefly addressed. Examples will be given on piezoelectric-based aeroelastic and hydroelastic energy harvesting in fluid-structure interaction problems. Elastic and acoustic wave energy harvesting by leveraging phononic crystal concepts will be discussed next with examples. Fiber-based flexible piezoelectric structures and their use in bio-inspired actuation and underwater locomotion will be summarized with brief examples. Our recent efforts on the use of an elastic waveguide with piezoelectric elements and an array of synthetic impedance circuits to enable digitally programmable piezoelectric metamaterials will be presented, with implications spanning from vibration attenuation to reciprocity breaking. An overview of our studies on wireless acoustic power transfer and ultrasonic data transmission using piezoelectric transducers will be followed by our ongoing collaborative efforts to enhance the accessible region of human brain by guiding leaky waves from the skull excited by piezoelectric transducers.

Through-wall acoustic energy transfer (TWAET) using piezoelectric devices is a technology proposed for wirelessly charging sensors in enclosed shells or vessels typically found in automobiles, space stations, and nuclear reactors. This mode of energy transfer has received significant attention in recent years as they outperform the traditional electromagnetic based through-wall wireless power transfer techniques which suffer due to Faraday shielding. Although useful, the existing framework is not suited to charge an enclosed sensor network. To address this shortcoming, we present, for the first time, acoustic holograms for selective TWAET and the details of the design, experiments, and potential applications.

This work introduces and investigates a metallic acoustic holographic lens to create an arbitrary acoustic pressure pattern in a target plane, using sound reflection phenomenon. The lens performs as a spatial sound modulator by introducing a relative phase shift to the reflected wavefront. The phase-shifting lens is designed using an iterative angular spectrum algorithm, and 3D-printed from powdered aluminum through direct metal laser melting. Then its capabilities to construct diffraction-limited complex pressure patterns and create multifocal areas are tested under water, numerically and experimentally. The proposed holographic lens design can drive immense improvements in applications involving medical ultrasound, ultrasonic energy transfer, and particle manipulation.

Large efforts are currently being spent in Europe for the maturation of innovative technologies enabling the application of morphing systems on next-generation civil transport aircraft. Running along with the CleanSky2 platform, the AirGreen2 project aims to evolve the proofs of concept addressed during the CleanSky program into true-scale demonstrators for a more comprehensive validation of morphing architectures both on the ground and in flight. In this challenging framework, research activities have been carried out to design a novel multi-modal camber morphing flap for the enhancement of the aerodynamic performances of a new-generation regional aircraft. Referring to CFD analyses, very relevant benefits in terms of CLmax increase and stall angle delay were proved to be achievable by properly morphing the camber of the flap; the extra-lift produced by flap cambering resulted more than adequate to allow for takeoff and landing at a single flap deployment angle, in turn much lower than those required by a standard flap in both settings. As a side positive effect, a dramatic simplification of the flap deployment system was shown to be practicable, together with the adoption of fairing-less (no-drag) solutions with flap tracks fully embedded into the wing. In addition, wing aerodynamic efficiency in cruise was demonstrated to be enhanced by locally morphing the tip of the flap still exposed to the aerodynamic flow in flap-retracted configuration. The design and validation of the smart architecture enabling the different morphing modes required for low speed (take-off / landing) and high speed (cruise) conditions, consisted of a complex process involving both wind tunnel and ground tests. To increase the relevance of the wind tunnel test campaign, a large scale-factor (1:3) was selected for the test-article, in combination with the realization of the very same Mach numbers expected in flight. Standing the un-scalability of the flap architecture conceived for ground tests and flight operations, a very challenging design was faced for the test article, in order to define a totally new morphable system (Fig.1), assuring the same functionalities of the true-scale device. The path followed to accomplish this task has been outlined in this work, with emphasis on adopted design philosophy, implemented methodologies, and technological solutions.

A modeling, experimental prototyping, and computational design exploration study of a morphing wing enabled by a tensegrity mechanism and actuated by shape memory alloy (SMA) wires is presented in this work. The studied wing design circumvents conventional control surfaces such as hinged flaps and ailerons through the implementation of a smooth wing shape that twists to modulate its flight characteristics. The continuous and smooth wing surface lessens aerodynamic drag to enhance aerodynamic efficiency. Computational fluid dynamic analyses confirmed superior lift-to-drag ratio of the twisting wing when compared to a conventional wing with a control surface. The morphing capability of the wing is enabled through an integrated lightweight tensegrity mechanism, which provides twisting motion through elongation/contraction of the SMA wires. Befitting for the actuation of the tensegrity mechanism due to their rod form, SMA wire actuators are incorporated to reconfigure the wing shape through thermally driven material actuation. The combination of a lightweight and compact tensegrity mechanism and SMA wire actuators eliminates the need for bulky components such as hydraulic and electric actuators to enhance the flight performance. A finite element model that integrates the wing, tensegrity mechanism, and SMA wire actuators is created to assess the stresses, maximum attainable twist angle, and structural mass of the wing. A design of experiment study is performed to evaluate the influence of the topological and geometrical design parameters on performance responses such as twist angle and mass. The most favorable design demonstrates a maximum twist angle of 15.85° and a mass of 2.02 kg without exceeding the material stress limits. The SMA-enabled torsional morphing capability is also demonstrated experimentally through a tensegrity twisting wing prototype equipped with commercially available SMA wire actuators.

Unmanned aerial systems (UAS) with embedded machine learning applications are applied in various fields for autonomous aerial refueling (AAR), concept of parent-child UAV system, drone swarm, teaming of manned aircraft and UAV, package delivery, etc. The fundamental challenge of an air-to-air docking phase is securing between a leader and a follower aerial vehicles with effective target detection strategy. This paper proposes an autonomous docking system for unmanned aerial vehicle (UAV) system that detects, tracks, and docks to a drogue. The proposed system is operated on an onboard machine learning computer platform. This paper presents not only the design of a probe-and-drogue type of docking system based on bi-stable mechanism, but also the development of an onboard machine learning system for a simple and a robust mid-air docking. ARM-based computer, Jetson Xavier NX module, is used as a companion computer to perform a real-time detection and an autonomous control for the aerial vehicle. To employ an effective drogue detection, a deep learning convolutional neural network (CNN) based real-time object detection algorithm, YOLOv4 tiny, is applied. Furthermore, a point-cloud based tracking algorithm with a RGB-D camera system is developed to track the drogue movement in the air. Before conducting an outfield docking test, a performance of the proposed docking system is validated.

A new branch of research in energy harvesting is flexoelectricity of solids. The flexoelectric effect is an electromechanical conversion mechanism that occurs in all dielectric materials. This can lead to new applications especially due to the larger number of possible materials. Therefore, investigation of properties of dielectric materials and specific conversion conditions are of great importance. Of importance is also finding out the significance of flexoelectric in relation to the piezoelectric energy conversion and possible other conversion mechanisms. This paper seeks to verify the flexoelectric effect in solid piezoelectric materials and to discover the usability for energy harvesting purposes. It follows earlier studies in this area only proving the flexoelectricity in non-piezoelectric materials. In our investigations, PolyVinylidene DiFluoride (PVDF) polymer films were used in a plate capacitor configuration. A measurement setup was built to enable the evaluation of polymer films under different temperature levels. Thereby, the pure flexoelectric behavior above the Curie temperature could be separated from the combined piezoelectric and flexoelectric effect at room temperature. In this way, an impression of the contribution of the flexoelectric effect in the energy conversion should be gained. As main parameters we used the change of electrical voltage and drift current in a differential measurement setup by means of a Lock-In Amplifier. The strain gradients in the material were generated by needles of steel with a vertical oscillation of the polymer film in relation to the needle tip. The results clearly show the presence of the flexoelectric effect and in this way also its contribution for energy conversion. The relative voltage and current drift response of the samples offer a great contribution of flexoelectric energy conversion under inhomogeneous mechanical loads.

We investigate piezoelectric energy harvesting on a locally resonant metamaterial beam for concurrent power generation and bandgap formation. The mechanical resonators have piezoelectric elements which are connected to electrical loads to quantify their electrical output in the locally resonant bandgap neighborhood. Electromechanical model simulations are followed by detailed experiments on a beam setup with 9 resonators. The locally resonant bandgap is measured and a resistor sweep is performed for each resonator to capture the optimal power conditions. Experimental efforts also include the DC combination of the separate harvester power outputs through full wave rectification of each output voltage.

One challenge in modelling a galloping piezoelectric energy harvester (GPEH) is the representation of the highly nonlinear aerodynamic force. The existing work in the literature employed various polynomial functions to fit the aerodynamic coefficient curve for simplicity, though their approximation capabilities are limited. In this paper, we propose to use the deep-learning technique to capture the aerodynamic force behaviour of a bluff body. Replacing the widely adopted third-order polynomial function by a welltrained artificial neural network (ANN) for aerodynamic force representation in modelling a GPEH, the feasibility of the proposed approach is preliminarily validated. To further improve the modelling accuracy, the electromechanical structure of the GPEH is then modelled using the finite element method. The trained ANN is integrated with the established finite element model to predict and update the aerodynamic fore applied on the bluff body in the real-time simulation. The aeroelastic motion and the electrical output of the galloping piezoelectric energy harvester are successfully predicted. Finally, based on a collection of experimental data, a welltrained artificial neural network (ANN) is proved to behave with a much better curve fitting performance than a third-order polynomial function. General procedures for using the deep learning technique to help model a general GPEH with complex geometric shapes are proposed.

Recent advances in the development of ultra-low power electric devices have drawn attention to the study of wind power generation flags based on piezoelectric elements. However, the piezoelectric film wind power generation method has been a challenge to improve power generation density and durability. Therefore, a new piezoelectric cylindrical shell wind power generation flag had been proposed by the authors as a flexible and durable power generation structure that utilizes vortex excitation vibrations. Preliminary experiments showed that it was expected to generate more than 10 times power than the conventional planar-shaped wind power generation flag. It is also shown through theoretical considerations that in order to construct a cylindrical generator flag using piezoelectric film that increased power generation in the low wind speed region, it was necessary to excite the vibration mode of circumferential wavenumber n=2 in order to utilize Kalman vortex excitation in this wind region. Moreover, in order to make the conventional structure, which generates power at high wind speeds, resonate at lower wind speeds, the radius of the cylinder must be large when the thickness was fixed and the thickness must be thin when the radius was fixed. However, the effect of variation of size on power generation characteristics has not been verified experimentally. In this report, wind energy harvesting experiments were performed with a number of flexible cylindrical shell type piezoelectric harvester flags, which has different dimensions and also thickness/radius ratios, and the structural design method to construct superior energy harvesting shell type generator, which will be able to generate large power at low wind speed, was discussed.

Based on the equivalent impedance analysis, a method is proposed to realize a coupled-field simulation study of piezoelectric energy harvesters of rectified interface circuits through an equivalent linear circuit. The method opens up opportunities for finite element packages to analyze, design, and optimize energy harvesters at a system level, either adding the capability of simulating rectified circuit interfaces, or reducing a nonlinear circuit interface simulation into a faster and more stable linear simulation that can be solved more conveniently. The nonlinear rectified circuit is replaced with an equivalent external linear circuit of two passive electrical elements in series. The types and values of the passive elements are explicitly determined for the standard AC-DC (SEH) and synchronized switch harvesting on inductor (SSHI) circuit interfaces. For validation, this equivalent linear circuit is applied to a bimorph beam harvester in ANSYS, and a system-level analytical approach is introduced which integrates two established analytical approaches. The agreement between the ANSYS results and those of the integrated analytical approach validates this equivalent linear circuit method and the integrated analytical approach.

The invisibility behavior of initiation and growing a delamination in an aerospace structure makes it one of the most dangerous and catastrophic damages. In this paper, the non-destructive testing (NDT) and structural health monitoring (SHM) techniques were used to visualize and quantify three different sizes of simulated delaminations inserted in a crossply CFRP plate. An experiment of using RollerFORM and OmniScan equipment was conducted to verify and visualize three simulated delaminations. The guided waves-based developed imaging methods with a sufficient network of piezoelectric wafer active sensors was performed to quantify the shape and size of simulated delaminations. The groupvelocity directivity plots were determined based on the mechanical properties of the interested specimen to estimate the group velocity values of incident and scattered waves. A simple method was developed to estimate the group velocity values of incident and scattered waves at each point of interested area based on the group-velocity directivity plots of propagating Lamb modes and the coordinates of transmitter and receiver transducers. The results demonstrate the capability of the developed imaging method for quantifying the size and shape of interested delaminations. The interaction of guided waves with delaminations were visualized experimentally using scanning laser Doppler vibrometer (SLDV). The effect of the delamination severity on the trapped waves generated over the delamination region was studied experimentally. It was found that delamination size can affect trapped waves. The large delamination has strong trapped waves compared with the small delamination which has weak trapped waves. The wavenumber analysis was conducted for the experimental wavefield data to study the effect of delamination severity on wavenumber components and to identify the delaminations. The result showed that new wavenumber components can affected by the delamination severity. The significant new wavenumber components due to strong trapped waves can be observed for the large delamination case.

A study has been conducted to evaluate the mechanical performance of various continuous fibers based on 3D printer technology. However, not only mechanical performance but also electromagnetic performance must be considered in aerospace industry. In this study, electromagnetic performance evaluation using a scanning free-space measurement (SFM) system was performed on 3D printed carbon fiber reinforced plastic (CFRP) and glass fiber reinforced plastic (GFRP) specimens in X-band (8.2 ~ 12.4 GHz). It was possible to measure and analyze the electromagnetic performance of composite specimens made by a 3D printer.

This research for the first time investigates the deployment dynamics of fluidic origami tubular structures, driven by internal pressurization using working liquid or air. Utilizing fluidics is attractive given that it is readily available in many engineering systems and is easy to realize and control, and embedding it in tubular origami is an effective innovation to create various advanced functionalities, which are not achievable in traditional origami even with adaptive materials. Despite fluidic origami’s potential as a promising inflatable deployable structure, the dynamics of its deployment have not been explored. This research advances the state of the art with intriguing new findings that have not been observed in previous studies and cannot be derived with traditional quasi-static analysis. In this investigation, the origami tube is constructed using the Miura origami pattern with the ends of the tube sealed and fluidic pressure applied in the chamber. We develop a structural dynamic model based on the bar-and-hinge approach, where the panel flexibility and inertia effects are captured. We restrict movement on one end of the tube in the axial direction and release the other end to move freely. We derive discretized non-dimensionalized equations of motion and apply equivalent nodal forces on the facets to emulate the effect of internal fluidic pressure. Through quasi-static analyses, the tube’s deployed configuration is shown as a function of the fluidic field pressure. It is illustrated that given the same pressure level, the structure will deploy to a lesser length/volume as the crease folding stiffness increases, and that the effect of the variation in panel deformation stiffness is not as significant. We then perform analysis of the tubular structure’s dynamic deployment process, by assuming a space-invariant pressure field first applied as a step function in time. The results reveal that the internal pressure level can effectively influence the structure’s transient response during deployment and its final configuration. Increasing the pressure level may increase the tube oscillation frequency, and may also cause the system behavior to change from overdamped to underdamped. These results indicate that adjusting the fluidic field pressure would vary the system effective stiffness and damping ratio properties, and thus would affect the tube’s transient dynamic response during deployment. Additionally, the multistability landscape of the fluidic tubular origami will further enrich the deployment dynamics. Under certain values of the fluidic pressure, the tubular structure exhibits significant global bending motion, and settles at a distorted stable equilibrium configuration with large transverse deformation. By applying the fluidic pressure as a ramp function in time, we show that through controlling the pressurization rate, the tube will possess different transient behaviors and settle at different stable configurations. Overall, this investigation enables a deeper understanding of the physics behind the dynamics of tubular origami deployment utilizing internal pressure and pave the way for potential applications of fluidic origami-based structures, such as space boom, morphing surfaces, soft robotics, and many others.

We present the theoretical and experimental investigation of a piezoelectric metamaterial-based acoustic black hole leveraging programmable shunt circuits. A versatile experimental platform is developed comprising a piezoelectric bimorph beam with 30 unit cells, each with a pair of piezoelectric patches with individually programmable shunt impedance. By varying the impedance applied to each unit cell, the local dispersion properties of the beam can be precisely controlled. In this work, we explore a programmable implementation of an acoustic black hole, in which wave packets are slowed down and compressed in space using a smooth gradient in shunt impedance.

We investigate a metamaterial beam with piezoelectric elements shunted to synthetic impedance circuits to demonstrate elastic wave trapping. We numerically and experimentally demonstrate the so-called rainbow trapping phenomenon, in which elastic waves of different wavelengths are trapped in different regions of the metamaterial beam. Guided by numerical simulations, experiments are performed on a beam with 30 piezoelectric elements with synthetic impedance circuits that have gradually varying inductance. Grading profiles are varied through the digital interface to understand its effect on the wave trapping behavior and conclusions are drawn.

In this work, the nonlinear behavior of the piezoelectric actuators are investigated from the experimental analysis of a piezoelectric-beam. A sequential experimental procedure is followed to study the elastic domain and the electromechanical coupling. Though this was done before, this time emphasis is also placed on other factors that may influence the experimental results. Experimental investigations are conducted to check (i) whether the way in which the fixed boundary condition is implemented induces any nonlinear behavior in the structure’s response, (ii) whether the air drag plays a role in the observed nonlinear effect and (iii) whether the dip in the input force and voltage levels, around the resonance, lead to the observed displaying the nonlinear effect. The results of these additional studies, along with the findings from the sequential experimental procedure, suggest a linear elastic behavior and a nonlinear electromechanical coupling in the piezoelectric actuators.

The traditional [0/90]T laminate has two stable equilibrium shapes, and it is possible to go from one shape to the other by means of an external force. In the past, researchers have attempted to obtain the snap-through between the two equilibrium states using smart actuators like shape memory alloy (SMA) wires and macro-fiber composite (MFC) patches. The integration of these actuators adds several complications. Moreover these smart actuators are generally attached to the surface of the laminate hence influencing the structural performance substantially. Recently, non contact magnetic actuation was experimentally demonstrated to be a viable method of reversible snap-through. A non-contact actuation using magnetic fields provides an elegant means of achieving reversible snapping without affecting the bistability characteristics of the laminate. In this work, a numerical model has been developed to aid the design of non-contact systems comprising of a ferromagnetic material actuated by a solenoid. The developed model uses a Rayleigh-Ritz based potential minimization to capture the magnetic snap-through of a hybrid [Fe/0/90/Fe]_T laminate. The model accurately captures the bistability of the multi-sectioned hybrid layup and can be used for the design of coils to provide the necessary actuation currents.

Piezoelectric materials are versatile. They were made into various successful engineering products, such as sensors, actuators, and generators. However, almost all of the previous designs were found only capable of one specific function among those three. From a more fundamental physical point of view, a piezoelectric element, as a transducer, provides a bidirectional channel for energy conversion between mechanical and electrical domains. It makes no bias to any of those functions. This paper analyzes the obstacle against developing multi-functional piezoelectric devices, clears that barrier, and further proposes a switched-mode interface circuit towards an unprecedented multi-functional piezoelectric design. It was developed based on a buck-boost switched-mode circuit. By properly controlling the switch actions, this interface circuit can realize all functions of dynamics sensing, energy harvesting (generation), and vibration excitation (actuation) in a time-sharing manner. The dynamics sensing function is realized according to the time ratio between piezoelectric capacitor discharging (through an inductor) and the inductor’s freewheeling. The discharging period is set to be as short as possible to avoid much interference to the stored charge of the piezoelectric capacitor, which is related to the dynamic displacement. The energy harvesting function is carried out by discharging the piezoelectric capacitor through an inductor (more drastically than that in sensing mode). The extracted energy in the inductor then freewheels into a storage capacitor. For the vibration excitation function, the control logic reverses. It first pumps energy from the storage capacitor to the inductor, then freewheels the energy to the piezoelectric capacitor. The actual control scheme is more complicated because the piezoelectric voltage is an ac output. The multi-functional design should comprehensively consider the discharging and freewheeling requirements under positive and negative polarities. Under these working principles, a prototyped multi-functional piezoelectric interface circuit is implemented and tested. The three functions are successfully demonstrated. By making a comprehensive collaboration between piezoelectric transducers and power electronics, this design starts a new chapter for the applications of piezoelectric materials toward multi-functional engineering designs.

Ultrasound acoustic energy transfer (UAET) is a transformative contactless energy transfer (CET) technology that outperforms conventional electromagnetic based CET techniques to recharge and communicate with low-power implanted medical devices which eliminates the need for invasive surgery. The limited modeling and proof-of-concept experiments on AET were performed in the linear range with several assumptions by neglecting the nonlinear wave propagation and the electroelastic nonlinearities of transmitter and receiver that become significant at higher source strengths and influence energy transfer characteristics. We present a series of experiments and experimentally-validated multiphysics models that we considered to address the knowledge gaps in UAET.

Flow in microchannels differs substantially from the flow in the macroscopic scale. Despite numerous works on two-phase flow and oscillatory single-phase flow in microchannels, oscillatory two-phase flow has not been thoroughly investigated. One of the situations where this type of flow occurs is in the ultrasonic drying device recently pioneered by Oak Ridge National Laboratory. An ultrasonic oscillatory piezoelectric transducer with microchannels is designed to dry the fabric by atomization and draining the water through the microchannel outlet. In this work, computational fluid dynamics is utilized to investigate the air-water two-phase flow driven by the ultrasonic vibrating microchannel. Our results indicate the importance of microchannel geometry and vibration conditions on drying efficiency.

In order to meet new manufacturing requirements, the implementation of smart materials in highly integrated mechatronic components, such as precision positioning systems in machine tools, is an alternative to bulky conventional electromechanical actuators. Magnetic shape memory alloy (MSM) actuators constitute an interesting alternative to both electromechanical and piezoelectric actuators. By harvesting the rotational energy of the tool body, it is possible to use MSM actuators together with permanent magnets to produce linear motions in the micrometer range. With the proposed approach, a higher level of integration is possible by eliminating the electronic control, thus reducing size and complexity of the system. This work presents a methodology for dimensioning MSM actuators excited by permanent magnets for producing linear motions in the micrometer range by exploiting the relative rotational motion of machine tool assemblies. The methodology consists in the simulation of the magnetic behavior of the actuator in order to predict the expected output stroke as a function of the magnet configuration. A novel concept for a fine boring tool with active cutting edge based on MSM actuation for finishing contoured cylinder bores in combustion engines illustrates the proposed methodology. Finally, a prototype was tested and the displacement at static and dynamic conditions in order to predict the corresponding contours at the cutting edge.

The continuous directed energy deposition (DED) method has been utilized to process various kinds of slender structures with different materials due to its uninterrupted characteristics. The characteristics of the specimen fabricated by this continuous DED method may not be the same as that in the conventional DED method due to different temperature histories. In this study, the characteristics of NiTi shape memory alloy on phase constituent and microstructure are investigated. Results indicate that the specimen fabricated with higher laser power shows more Ti2Ni precipitation, increased defects (e.g., voids, inclusion, etc.), and larger grain size. The microstructure at different regions presents diverse morphologies, which change from columnar dendrite to equiaxed grain to columnar dendrite due to different cooling rates. The preliminary study in this paper is expected to lay the foundation for the fabrication of NiTi slender structures with the continuous DED method.

Traditional textile structures made of multifunctional materials leverage unique material behaviors through a hierarchical manufacturing process to develop tailored solutions applicable to robotic, transportation, and medical device industries. For example, knitted and woven textiles made of shape memory materials can provide high force and distributed motions for programmable surfaces, soft robotic grippers, and active compression garments. Additionally, 3D spacer fabrics with superelastic materials can provide constant force profiles, enhanced damping frequency ranges, and large energy dissipations for prosthetic attachments, helmet technology, and impact resistance fortifications. Usually, researchers manufacture multifunctional textiles with monofilament and yarns but recently, over-twisted coiled structures have demonstrated improved actuation contractions, force generations, and strain recovery. This research presents the creation of NiTi microfilament over-coiled yarns within textile structures, demonstrating their dual potential as high force linear actuators from the shape memory effect, and compact energy absorbers from superelasticity. To highlight the actuation potential of NiTi over-twisted coiled yarn textiles, the coiled yarns were integrated in parallel within a woven textile. The over-twisted coiled weave was experimentally investigated for actuation contractions, and generated forces. For energy absorption, the NiTi over-twisted coiled yarns were structured within a 3D spacer textile structure, and experimentally investigated quasi-statically for strain recovery and energy absorption through hysteresis, as well as dynamically for mapping damping performance dependent behavior. This work expands the profile of NiTi based multifunctional textiles to offer improved and tailored solutions for actuating and energy absorbing technologies.

Multifunctional capabilities of Shape Memory Alloys (SMAs) and, more specifically, their inherent characteristic of producing and recovering transformation strain under thermal stimulus, render them ideal for actuator appli- cations. In fact, SMA actuators are widely used in various fields including but not limited to robotics, medical, civil, and aerospace engineering. Moreover, they are also able to be formed in a wide range of shapes that includes, but is not limited to, wires, ribbons, bars, torque tubes and various spring types. This fact combined with their high-energy density, the noise-less, spark-free, and debris-less operation and their compactness renders them ideal for aerospace morphing structures where weight, volume, energy consumption, and other operational specifications have to be strictly met. In this study, two SMA actuator forms, one linear, i.e., wires of circular cross-section, and one torsional, i.e., torque tubes, are compared in terms of weight/volume, stroke capabilities, developed stresses, cooling requirements, power consumption and overall operation under predefined conditions. The actuators are intended for use in parts of an articulated shape adaptive mechanism envisioned for altering locally the outer mold line of a civil supersonic aircraft. The morphing system is placed on the lower part of the fuselage in order to alter the aerodynamic profile and reduce the sonic boom created during supersonic flight over inhabited areas. The specifications for the design of the actuators are provided and finite element analysis is used to verify the overall response of the SMAs.

In this research, the morphing wing geometries are studied parametrically to identify the aerodynamic characteristics at various flight conditions. The morphing wing presented considers a NACA 0012 airfoil with a rigid portion at the leading edge and a continuously conforming trailing edge flap. Following the authors' previous study, an elliptical curve was used as the morphing model for the spanwise trailing edge deflection. Control deflection for the trailing edge, hinge location, Reynolds number, and angle of attack were parameterized to investigate trends. This research was conducted numerically through Computational Fluid Dynamics (CFD) simulations. The CFD simulations are performed using the three- dimensional (3D) Reynolds-Average Navier-Stokes (RANS) equations with the k – ω Shear Stress Transport (SST) turbulence model. The results showed that a higher Reynolds number leads to better aerodynamic performance while the control deflection and hinge location needs to be optimized for a given flight condition. The results also indicated that the morphing wing shape optimization should start from lower values of control deflection and hinge location as an initial design approach. The study demonstrates that morphing wings can achieve significant aerodynamic performance gains through active actuation of hinge point location and control deflection to suit the flight regimes encountered through a mission profile.

Studies regarding concurrent wind-flow and base-motion energy harvesting have drawn increasing attention in recent years. However, for conventional wind energy harvesters under such dual excitations, the base-excited inertial vibration and flow-induced aeroelastic vibration supplement with each other only within a narrow range of frequency near the resonance. Within this range, aeroelastic vibration frequency is locked into the base vibration frequency where the two sources are concurrently contributing to power generation; while the concurrent feature is lost outside this range. Internal resonance in multimodal systems has been utilized in recent years for efficiency improvement in pure base vibration energy harvesters. The merit comes from the fact that energy can be pumped from other modes to the power generation bandwidth, broadening the bandwidth toward both lower and higher frequency regions. In this paper, a broadband galloping-based aeroelastic energy harvester with internal resonance is proposed for the purpose of efficiency enhancement in concurrent wind and base vibration energy harvesting. Two-to-one internal resonance is aroused by arranging two sets of magnets symmetrically at the beam connection. Numerical solutions are calculated for the fully coupled aero-electro-mechanical model. A significantly widened lock-in bandwidth with multiple power peaks is achieved for effective concurrent wind and vibration energy harvesting.

Non-resonant harvesters such as piezoelectric cantilever beams that extract energy from turbulence-induced vibration are often nonviable alternatives to their resonant counterparts. In the quest for enhanced viability, such fluidic harvesters can be positioned side-by-side and incorporate the aerodynamic coupling between them to improve power output. In this paper, we derive the power budget and electromechanical efficiency of two side-by- side beams subjected to an impact load in quiescent flow and grid-generated turbulence. We also introduce the aerodynamic coupling-to-input ratio and aerodynamic coupling effectiveness as ways to measure the influence of the aerodynamic coupling on the energy conversion process. The theoretical derivations are used to evaluate the aforementioned terms for two cases: (i) one beam subjected to a ringdown test in quiescent flow and (ii) both beams exposed to grid-generated turbulence. The influence of gap-to-width ratio, mean flow velocity and distance from the grid on each term has also been considered in this analysis. Our results show that while the aerodynamic coupling-to-input ratio exponentially decays with respect to the gap-to-width ratio for the ringdown test case, it remains relatively constant and non-zero with increasing gap-to-width ratio for the turbulence cases considered.

As the demand for microsatellites increases, deployable structures have been used to increase mission performances of microsatellites. Tape spring based deployable structures are lightweight and they can be constructed to have high packaging efficiency; they are suitable for microsatellites. This paper presents a meter-class deployable structure for microsatellite using tape spring. This structure is stowed in a volume of 1U CubeSat and after deployment it has an area of 1m2 with natural frequencies over 10 Hz. Modal analysis was performed to check the stiffness requirement after deployment. Deployment tests were performed to validate the deployment reliability, and the deployment accuracy.

This paper presents the concept design, preliminary experimental validation, and performance evaluation of a novel bio-inspired bi-stable piezoelectric energy harvester for self-powered fish telemetry tags. The self-powered fish tag is designed to externally deploy on fish (dorsal fin) to track and monitor fish habitats, population, and underwater environment, meanwhile, harvests energy from fish motion and surrounding fluid flow for a sustainable power supply. Inspired by the rapid shape transition of the Venus flytrap, a bi-stable piezoelectric energy harvester is developed to generate electricity from broadband excitation of fish maneuvering and fluid. A bluff body is integrated to the free end of the bistable piezoelectric energy harvester to enhance the structure-fluid interaction for the large-amplitude snap-through vibrations and higher voltage output. Controlled laboratory experiments are conducted in a water tank on the bio-inspired bi-stable piezoelectric energy harvester using a servo motor system to simulate fish swing motion at various conditions to evaluate the power generation performance. The preliminary underwater experimental results demonstrated that the proposed bio-inspired bi-stable piezoelectric effectively converters fish swing motions into electricity. The average power output of 1.5 mW was achieved at the swing angle of 30° and frequency of 1.6 Hz.

This paper proposes a vision-based collision avoidance system for unmanned aerial vehicles (UAVs). A method to detect and avoid approaching objects is necessary for UAVs since they are inherently vulnerable to external impacts. To resolve common issues with motion detection on a moving platform, computer vision algorithms such as optical flow and homography transform are utilized. The robustness of these algorithms is improved by employing characteristics of differential images. The proposed method is implemented in a camera-equipped onboard computer and then mounted onto a UAV as a collision avoidance system. It performs evasive maneuvers to avoid various objects thrown in its flight path, demonstrating its functionality and robustness.

Cable vibration and monitoring the cable maintenance are inevitable parts of cable bridges. To integrate both problems, the electromagnetic (EM) devices are proposed to self-power damper and studied in various ways. The conventional EM devices have a lack of damping performance that additional damping is needed to mitigate the cable vibration. Therefore, the regenerative hybrid electrodynamic damper (RHED) is developed to increase the damping performance which can mitigate the cable vibration properly while electrical energy is generated. In this study, experiments for mechanical damping of RHED and vibration induced electrical energy are conducted to investigate the RHED configuration. The applied damper has various characteristics that can be used in civil engineering such as high induced voltage and variation of damping force. The damping force is varying according to external resistance and condition of excitation. The characteristics of RHED are considered to produce the energy harvesting circuit. This study increases the harvesting energy and charges the rechargeable battery through the proposed circuit. Besides, the proposed harvesting circuit perform more than 70% efficiency in certain excitation. As the result, energy harvesting and damping mechanism can be utilized simultaneously by grasping the relationship between the RHED and a circuit.

Energy harvesting from oscillating structures receives a lot of research attention as these applications appear promising for the continuous energy supply of low power devices. Recent studies indicate increased power production of piezoelectric energy harvester configurations undergoing severe nonlinear vibrations, but the obvious drawback is the increased complexity of the coupled electromechanical dynamic response of the harvester. The current study focuses on the development of a robust and accurate numerical tool capable of modelling and design of such systems. This model is used to simulate the electromechanical response of composite strip structures equipped with piezoelectric devices subjected to nonlinear oscillations under compressive loading and near buckling instability conditions. The study is combined with experimental verification studies on a fabricated harvester prototype aiming to validate the numerical tool and to corroborate the electrical voltage generation on the piezoelectric devices. Additionally, a preliminary experimental study is performed to quantify the available electrical energy that is produced from the oscillating structure. Three different harvesting circuits are studied and their energy conversion performance is investigated. Measured results validate the developed numerical tool. Moreover, the increased electrical voltage and charge generation during the geometrically nonlinear oscillations as the prebuckling load increases, increasing also the available electrical power on the circuits, is illustrated numerically and experimentally.

The article presents the development of a self-powered rectified electromagnetic energy harvester (EMEH) under low frequency excitations. To overcome the drawback of low output voltage across the small optimal load, it is proposed to use the transistor-based rectifier biased by the self-powered SECE-based piezoelectric energy harvester (PEH). In addition, the buck-boost converter controlled by the self-powered SSHI-based PEH is im- plemented for the maximum power point tracking. A semi-analytic model is developed for predicting the peak power and the optimal load used for designing the buck-boost converter. The prediction is then validated by experiment showing 1.5 mW optimal output power. Further, it is found that the 0.22 low rectified voltage is increased up to 2.5 V by the proposed SSHI-based voltage boosting technique. It offers advantages of zero quiescent power dissipation and the ease of tuning the input impedance of the buck-boost converter by varying the SSHI load impedance.

Topological metamaterial has become a research hotspot recently, owing to the unique features, including wave localization and topological protection. In this paper, we are motivated to introduce the topological metamaterial into vibration energy harvesting. The proposed topological metamaterial vibration energy harvester (topological meta-VEH) consists of two topologically different sub-metamaterials and a piezoelectric transducer mounted at the conjunction of these two sub-metamaterials. First, the governing equations of this electromechanical system are derived. Then, the band structure and dispersion relation of this topological meta-VEH is obtained by applying the Bloch theory. To obtain the transmittance response, the finitely long model of the proposed topological meta-VEH is formulated, the corresponding analytical solutions are obtained as well. From the theoretical analysis, it is found that the topological interface mode takes place at the first Brag band gap and it has the capability of concentrating elastic wave energy at the interface so that the piezoelectric transducer at the conjunction can generate large output power. Analytical results indicate that the topological meta-VEH is a novel and outstanding method to achieve high-efficiency energy harvesting.

Structural control of civil infrastructure in response to large external loads, such as earthquake or wind, is still not widely employed due to several key issues, such as latency in the system and challenges with information exchange. To promote information flow, wireless sensor networks have emerged as a potential solution that is also a low-cost alternative to the traditional wired sensing and actuation infrastructure. However, these systems also introduce additional challenges such as latency in the wireless communication channel and computational inundation at individual sensing nodes. Inspiration can be drawn from the real-time sensing and actuation capabilities of the biological central nervous system to overcome some of these challenges experienced by wireless sensor nodes. A novel bio-inspired wireless sensor node was developed that is capable of real-time time-frequency decomposition of a sensor signal, thus drawing inspiration from the frequency selectivity of certain neurons. Similar to the functionality of neurons, the node uses asynchronous sampling based on the content of the perceived signal, resulting in large power savings and compressed data communication. In this study, the bio-inspired wireless sensor node is utilized for a feedback control application in order to overcome the challenges currently seen in wireless control. The sensor node is able to transmit frequency- specific data in real-time to a controller node which constructs a control force using minimal computational resources. This study validates that performance of the bio-inspired wireless feedback control architecture on a one-story partial- scale shear structure that is seismically excited and controlled via active mass actuators.

Although heart disease is still the major cause of death in the world, cardiovascular mortality rate has decreased over the past years, which is mainly related to invention of different types of circulatory assist devices. Therefore, focus of recent studies lies at developing the cardiovascular assist technologies to further decrease mortality rate. Currently, impeller-driven and centrifugal pumping technologies are the state of art for artificial heart applications. These types of pumps are able to lengthen lives, however their operation produces blood damage(hemolysis) which makes them not suitable for long-term applications. A natural solution to the need to artificially pump blood over long time frames while accruing less blood damage can be found in peristaltic pumps. The peristaltic pump design discussed herein mimics the heart’s natural operation by using magnetoactive elastomers that respond to the presence of external electromagnetic fields. Utilization of a magnetorheological (MR) elastomer rather than rotating rollers could constitute a materials-based solution for solving the mechanical issue of hemolysis by avoiding impellers. Additionally, the mechanism produces desirable pulsatile flow. In this work, a magnetically driven peristalsis pumping mechanism is proposed and simulated using fully coupled finite element simulations in COMSOL Multiphysics. The primary goal of this work is to develop high(er) fidelity simulation of the working peristaltic pump in order to determine how design factors and the pumping mechanism affects hemolysis. Power law damage metrics, beyond basic flow shear stresses, were used to compare the hemolysis index in the proposed model with the results from previous works. Results show that blood damage at higher magnetic fields strength was larger than weaker applied magnetic field. Regardless of the magnetic field strength, average blood damage was higher approaching the outlet versus the inlet. In addition, this study shows the efficacy of the device geometry and means of operation which can be intermediate optima pointing toward possible optimization of peristaltic pump to increase the efficacy of the pump.

In this study, we explore the postbuckling instability of piezoelectric-integrated cylinders under axial displacement for energy harvest applications. Experiments are conducted using 3D printed cylinders with piezoelectric transducers bonded on their outer and inner surfaces. The local and global postbuckling responses of the cylinders are triggered based on their design and geometry. Numerical simulations are carried out to study the effect of varying cylinder geometries on the harvested energy. A comparative study is performed between the numerical and experimental results. Furthermore, a corrugated design is proposed to tailor the postbuckling response of the cylinders from local buckling to global buckling. The results shows that the new corrugated designs for the cylinders improves the energy harvesting efficiency.

The nonlinear beam-slider structure, which consists of a nonlinear cantilever beam and a free movable slider, can always obtain the high-energy orbit to achieve passive self-adaption in a wide bandwidth. The efficiency improvement of this structure has been demonstrated in energy harvesting application. In this work, the nonlinear beam-slider structure is applied as a vibration neutralizer. The behavior of the 2-degree-of-freedom (2-DOF) vibration system is investigated experimentally. The trajectory of the slider, time history response of the nonlinear beam and the linear primary structure are recorded simultaneously. The results show that the nonlinear neutralizer with appropriate parameters has broader bandwidth than the linear one. However, there are multiple solutions corresponding to different vibration states of the nonlinear neutralizer in the suppression frequency range. The vibration of linear primary structure can be suppressed only when the nonlinear neutralizer obtains the certain energy orbit at the given frequency range. The free movable slider can assist the nonlinear beam to obtain the high-energy orbit in multi-solution range (28 Hz-31 Hz). In the frequency range of 28 Hz-31 Hz, the nonlinear neutralizer on the high-energy orbit enhances the vibration suppression performance.

This paper proposes a concept of a deployable tubular structure with the Yoshimura pattern based upon a novel folding approach. The developed folding approach is based on the reconfiguration of the Yoshimura tubular structure into the intermediate configurations. All the possible candidates of the intermediate configurations are derived with respect to the design parameters. The structural behavior during the reconfiguration process is analyzed to figure out the driving force for the deployment and the stability of the structure. The deployment of the Yoshimura tubular structure is demonstrated through the prototype with active hinges made with shape memory plastic.

This work aims at solving these issues, through developing a tribo-induced color tuner which can be integrated into the vastly-distributed commercial solid-state lighting (SSL) system. Through this approach, the sensing is achieved by the tribo-induced time-variant color without the need of pre-amplification, which can be wirelessly transmitted with no additional energy consumption, and the signal can be sent by everywhere-existed lamps and processed by everyone-owned smartphone cameras or closed circuit televisions (CCTVs). The accurate self-powered wireless sensing of the rotation speed was performed, with the accuracy evaluateddemonstrated. The smart lighting and an underwater photographing system were demonstrated by the developed color-tunable SSL system with the best photographing quality achieved.

Programmable surfaces and structures are mechanisms that transition between two or more geometric configurations. Programmable surfaces capable of altering their topology with a change in operational conditions have the potential to enable a wide range of applications in a variety of domains like haptics, wearables, human-computer interactions, fluidsurface interactions, and shape morphing structures. Prior research on programmable surfaces has developed various techniques to realize shape change applications. 4D printing includes multi-material printing of mechanisms that transform from any 1D or a 2D shape into a 3D shape using simple energy inputs like heat, water, or light. Additionally, origami composite structures with selective actuation of shape memory polymers also afford complex shape changes. We present a novel approach to designing programmable surfaces by incorporating shape memory alloys (SMA) and textile manufacturing processes to form variable topology programmable surfaces from knitted active textiles. Thermally responsive shape memory alloys (SMAs) leverage solid-state phase transformations and the shape memory effect to return the material to a predetermined state upon heating. The shape memory effect enables creation of multi-stiffness SMA configurations that can be utilized to develop structures with tunable surface topographies. Active knitted textiles act as programmable surfaces by transforming from an inactive 2D flat surface in the cold, flexible martensite state into active 3D surfaces when heated above the austenite finish transformation temperature.