This PDF file contains the front matter associated with SPIE Proceedings Volume 12483, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Tensegrity structures have been harnessed in the design of many reconfigurable and deployable systems due to their high strength to weight ratio, stiffness tunability and multistability programmability. In this paper, we present a design methodology of an origami-inspired multistable tensegrity structure that can achieve up to three stable configurations in one unit cell. This class-3 tensegrity structure can achieve equilibrium states at the fully deployed and flat folded states, and the transition between its stable states is controlled with a one directional displacement, a feature not observed in previous tensegrity elements. To design this system the required input are the three heights at which a stable configuration is desired. At each height the total strain energy of the system of strings is evaluated to select the unstretched length and stiffness values of each string that satisfy the conditions of stability. Analytically it was found that achieving a stable configuration at each height is affected by the number of strings that are in tension at this point, and the deformation path, stiffness and unstretched length of each string.

This paper presents an experimental investigation on the origami patterned cylinder made of Tachi-Miura Polyhedron (TMP) unit cell. The unit cell shows strain-softening behavior under compression load. To analyze the effect of nonlinear behavior on the elastic wave propagation in TMP cylinder, fabrication of metallic origami cylinder and impact test were conducted. The thin metallic structure was fabricated using the vacuum bag method. The pressure was applied evenly to the aluminum facets, which have compliant hinges that behave like torsional springs. The first unit cell of the cylinder structure was connected to the dynamic shaker and the pulse load was applied. To measure the dynamic behavior of unit cells during elastic wave propagation, the stereo pattern recognition (SPR) camera system was employed. The experimental result shows that the compressive wave, induced by impact load, was attenuated due to the nonlinear characteristics of the TMP unit cell. Furthermore, the tensile wave, which emerged later, arrived first on the last unit cell. It means that the tensile wave overtook the compressive wave. The speed of the elastic wave is affected by the stiffness of the structure. Based on the strain-softening behavior of the TMP unit cell, the compressive wave is slower than the tensile wave. It induced the attenuation of compressive impact and overtaking of tensile elastic wave. We can expect that this nonlinear characteristic of the origami-based structure can be applied to the shock mitigation structure.

Automotive and defense industries have been calling for the lightweight materials and structures with excellent energy absorption property under extreme operating conditions. Toward this end, random foams, and architected materials with different building blocks (beam, plate, and shell) have been investigated. However, most of the studied metamaterials exhibit anisotropic mechanical behavior upon different loading conditions. In practice, engineering materials are mostly expected to display isotropic mechanical properties at the macroscopic level. Random foams have been reported the first-generation man-made porous isotropic metamaterials, but they are characterized by the stochastic, uncontrollable topologies and material distributions which make them inferior candidates by contrast to architected metamaterials. In this work, we conducted systematically numerical experiment on a novel design of hybrid SC-BCC foam structure, which exhibits nearly isotropic mechanical behavior with nearly linear scaling relationship between relative stiffness and relative density. Remarkably, the proposed hybrid foam shows significantly improved stiffness, yield strength, and energy absorption compared to SC-foam. The stiffness and strength of hybrid foam are increased by 237% and 177% compared to SC-foam. The energy absorption of hybrid foam is increased by 96.5% and 28.1% compared to SC-foam and BCC-foam, respectively. The findings in our work offer new insights to design isotropic architected materials with enhanced mechanical performance that can find applications ranging from structural components of defense systems to protection systems in vehicles.

2-D lattice structures have gained considerable attention over the past few decades due to their high strengthto- weight ratio. Enormous studies have been conducted on various shapes of the 2D lattice structures. Different shapes of the 2-D lattices exhibit different Poisson's ratio values. The Poisson's ratio ranges from negative to positive values for conventional lattice structures such as honeycomb and auxetic honeycomb lattice structures. However, there exist such lattice structures that exhibit Zero Poisson's Ratio (ZPR). In this article, we propose a novel hourglass structure (HG) that exhibits Zero Poisson's Ratio (ZPR HG), studied dispersion behaviour, and compared with negative (Aux HG) and positive (Hcb HG) Poisson's Ratios. The emergence of the band structure in the HG-ZPR has been studied analytically and compared with the conventional hourglass structures that exhibit positive/ negative Poisson's ratio. The dependency of the band structure on Poisson's ratio has been investigated. A significant variation in the band structure has been observed as the microstructure of the hourglass structure varies. This study intends to provide the necessary physical insights showing the dependency of the band structure on Poisson's ratio.

Bridge pier is the key components for transferring loads between the bridge and foundation. Its status significantly impacts on the safety of the entire bridge. While the sudden external force (e.g. vehicle collision, explosion, earthquake etc.) could cause catastrophic properties loss and casualties. Therefore, many anti-collision implementations are used in the bridge pier. The rigid protections and soft buffer structures, which are the conventional anti-collision methods. The former cannot lower the damage to vehicle and passengers, and the latter is capable of withstanding the minor or moderate vehicle collision only. In order to overcome the shortcomings of the conventional anti-collision method, tensegrity as a prestressed tensioned structure is proposed to be integrated with the bridge pier as a shielding component. The integrated tensegrity can absorb impact energy of the vehicle-pier-collision through large deformation or localized damage to protect the core pier. Therefore, this paper proposed a detailed anti-collision design with integration of tensegrity for the bridge pier. Additionally, the assessments of its statics and dynamics are given. Furthermore, the anti-collision effect has been illustrated, numerically. The process of the vehicle-pier-collision in three different velocities were simulated by ANSYS/LS-DYNA; the energy absorption is analyzed. The relationship between deformation state and absorbed energy was also obtained. Therefore, the feasibility of the proposed design has been fully explained. It provides an option for the anti-collision design in the bridge pier.

The positioning of resonators of locally resonant mechanical metastructure with finite resonators is presented to increase the bandgap. Based on the modal analysis solution of mechanical metastructure with finite resonators, the bandgap change according to aperiodic positioning of finite resonators under the fixed mass ratio of main structure to resonators is observed. By utilizing the responses of the main structure with single resonator having various positions, resonator positions for effective vibration attenuation are selected. Mountain frequencies overlapping between resonators is considered from the main structure responses with single resonator, positions for the enlarged bandgap width are obtained. By increasing the number of resonators and positions, mass distribution effect is added in bandgap formation according to resonators’ position of resonators. Using these results, effective resonator positions and mass distribution for each mode of mechanical metastructure with finite resonators under limited mass ratio of main structure to resonators are proposed.

Metamaterials with locally resonant unit cells based on piezoelectric shunting have led to a new way of realizing elastic/acoustic wave manipulation with online tuning capability. One limitation of uniform locally resonant metamaterials with identical unit cells is their relatively narrow bandgap. Recently, the concept of graded metamaterials with non-uniform local resonators has emerged as a promising approach for improvement. In this research, we explore an adaptive piezoelectric metamaterial-based metamaterial design with spatially varying piezoelectric shunt circuits integrated with negative capacitance. Through systematic parametric analysis, a new design is identified to take advantage of the graded resonant shunt to enhance wave manipulation performance and enlarge the bandgap. Case investigations are presented to demonstrate the feasibility.

Low-frequency bandgaps are generally achieved by using locally resonant metamaterials at much higher wavelengths than the lattice constant. However, it remains a challenge to control wave propagation and vibration in these structures due to the limited number of conventional options available as periodic unit cell arrangements. This work investigates the band structure of flexural waves in a metamaterial sandwich beam with an hourglass lattice core using the transfer matrix method. The double dome-shaped hourglass unit cell is modelled with different non-dimensional geometric ratios. A sandwiched metamaterial beam model is then established using a periodic finite hourglass array, considered under the flexural wave propagation. The complete hourglass sandwiched system is further studied to obtain the bandgaps corresponding to the microstructure of the hourglass which is varied in the frequency domain. Subsequently, parametric analysis is performed using some specific non-dimensional geometric parameters that are found to be sensitive towards tailoring the mechanical properties of such unit cells. This study builds a foundation for modelling lightweight hourglass lattice sandwich beams with complex dome shape structures and presents guidelines for designing sandwich beams to control wave propagation.

In this presentation, I will introduce our recent advances on controlling acoustic wave propagation via spinning media. We will start from a review of the theoretical framework for the scattering problem by a rotation object. Then we will introduce a generalized scattering cancellation theory (SCT) to cloak spinning objects from static observers. In another example, we will study the torque and force a spinning cylindrical column of fluid experiences in evanescent acoustic fields, and show that the resulting discontinuity can scatter sound in unusual ways, e.g., a negative radiation force.

This research experimentally investigates the integration of mechano-intelligence into mechanical metastructures for self-adaptive wave control. We created a phononic metastructure prototype utilizing periodic buckled beam modules that has highly adjustable wave propagation characteristics via length reconfiguration using a linear displacement actuator. By utilizing the physical reservoir computing framework, we show that the proposed metastructure can recognize and self-adapt to different inputs by making decisions on appropriate actuations to reconfigure itself to achieve an intelligent wave blocking task. Overall, this research provided a promising approach for constructing and integrating functional mechano-intelligence in structures harnessing physical computing and learning, and created a new direction for the next generation of adaptive structures and material systems.

Active mechanical metamaterials have shown a glimpse of their capacity to create the foundation for intelligent matter. This study presents the concept of mechanical metamaterial electronics (meta-mechanotronics) to design intelligent matter with information processing capability. This advanced functionality is achieved by fusing the mechanical metamaterials, digital electronics and nano energy harvesting technologies. Electronic mechanical metamaterials explored under the meta-mechanotronics paradigm rely merely on their constituent components to perform self-powered mechanical-electrical-logic operations. A proof-of-concept digital unit cell is presented as the 2-bit building block for electronic mechanical metamaterials. The digital unit cell is rationally designed as a monostable origami-inspired metamaterial with twist buckling behavior and specific multi-motion properties to synthesize discrete mechanical configurations and realize digital logic gates. Experimental studies are performed to evaluate the digital computing performance of the designed mechanical metamaterial logic gate.

A tunable metasurface consisting of an array of piezoelectric unit cells is demonstrated to anomalously refract incident elastic wavefronts along a target direction. Each surface bonded transducer (PZT) is shunted with an individually calibrated synthetic inductor to form a local resonator, which is then tuned to modify the local dispersive characteristics of each unit cell and implement discrete phase shifts. The analog synthetic inductances are integrated with digital potentiometers to realize online tunability, allowing the metasurface to be recalibrated to accommodate different incident wave frequencies or target angles of refraction without requiring any physical alteration of the host structure. A microcontroller unit (MCU) then reads the stored empirical data and designates the appropriate settings for each digital potentiometer in order to realize the targeted waveguiding behavior for a specified incident wave frequency.

Embedding SMA layers in a composite structure is a promising technology to improve mechanical features, but this achievement must not come at the cost of structural integrity. The research carried out within this paper was focused on assessing the delamination behavior of hybrid composite structures, specifically, ones composed of layers of a Cu-based shape memory alloy (SMA) and a glass-fiber reinforced polymer (GFRP). Different patterns of holes cut into SMA layers of a composite material have the potential to produce topologies that can be applied for improved damping in lightweight structures. To make an initial assessment of the effects of different hole patterns on the structural integrity of the composite, the authors have designed an experimental setup intended for the application of Mode II (shear) loading to the composite samples up to the point of failure.

The efficacy of using piezoelectric actuators to initiate the dynamic deployment of bistable composite tape springs is evaluated in this paper. Ultra-thin composite booms such as tape springs and their cross-sectional variants have seen increased popularity in spacecraft structures due to enabling the precise deployment of flexible solar arrays, sails, reflectors, and antennas. They can elastically transition between the deployed “extended” position and the stowed “coiled” position while retaining superior stiffness, thermal properties, mass efficiency, and compactness when compared to thin-shelled metal booms and rigid articulated columns. Bistability in the coiled and extended states allows the boom to exhibit more controllable self-deployment and become reconfigurable, which could allow spacecraft to relocate, redeploy, and adapt to changing environmental conditions or mission objectives. Deployment systems commonly include motors and mechanical restraints that significantly contribute to mechanical complexity and spacecraft weight. Since bistable booms do not rely on elastic instability of packaging to initiate motion, a non-intrusive and lightweight actuation mechanism is needed to trigger deployment. This paper experimentally demonstrates how a Macro Fiber Composite (MFC) actuator can statically and dynamically excite a stowed composite tape spring to initiate unrolling into its extended state.

This paper introduces an ultrasonic piezoelectric transducer consisted of a concave shaped piezoelectric film and a support with an air cavity for vibration. The high flexibility and sensitivity of the transducer are guaranteed by utilization of Polyvinylidene fluoride (PVDF), and these are important in designing transducers of good acoustic performance. Ultrasound pressure results of the transducer are measured from frequency sweep inputs. From the results, we observe that the concave case generates several resonant peaks within a specific frequency range. Additionally, the sound pressure change of the transducers with different radii of curvature is investigated. The experimental results demonstrate that radius of curvature contributes to the sound pressure magnitude significantly.

In this paper, we present a novel structural identification method using semi-active inputs generated by piezoelectric transducers. Structural identification using input and output information provides an accurate structural model. Conventional identification uses a maximum-length sequence, whose signal shape is similar to a square wave, as input. To generate inputs suitable for identification, several devices are required. These devices consume a lot of energy. If inputs are generated by a small number and simple design devices with low consumption, structural identification will be more practical. Piezoelectric semi-active control has been used in the research field of vibration control. This control generates a semi-active input whose signal shape is similar to a square wave. The semi-active input is generated by a simple circuit. The generation of the semi-active input consumes little energy. Therefore, the semi-active input has the potential to be used as an identification input instead of the maximum-length sequence. The property of the semi-active input is related to the generation strategy. This paper proposes a novel strategy to generate a semi-active input suitable for identification. Due to the unique mechanism of semi-active input generation, the novel strategy sometimes has the problem of generating semi-active inputs that are not suitable for identification. This paper discusses the reason and the solution to this problem. The feasibility of semi-active identification is presented through the numerical simulation and validation experiment. The identification result of the proposed method was close to the exact model. The proposed method achieved a 99% reduction in energy consumption.

This paper presents a fundamental non-contact valve design developed by integrating a ring-stack piezoelectric actuator into a converging nozzle design to impart harmonic flow. The paper also outlines the governing equations as well as limiting factors that constrain the design and operating performance. The converging nozzle design achieves choked flow at the valve exit when the nozzle is fully open. Valve actuation centers around piezoelectric ring stacks: the piezoelectric stack is fixed within the valve on one end to the base plate and has a conical nozzle tip attached to the opposite end of the stack. When the stack fully displaces to its maximum length, the nozzle tip is in the closed position where minimal flow passes through the valve exit. The flow area between the nozzle tip and casing wall achieves maximum mass flow rate when the piezoelectric stack is at minimum length. The change in flow cross-sectional area due to the piezoelectric stack displacement generates a change in mass flow rate through the valve. Due to the small-scale displacement of piezoelectric stacks, different angles of the nozzle cone and casing are required to achieve a greater desired mass flow rate. This model is adjustable to accommodate various piezoelectric stack sizes and displacements or to alter the exit mass flow rate to best suit a particular application.

This paper proposes a geometrical method to determine ambiguity that arises in metamaterials that displays discontinuity in refractive index in the frequency spectrum. Three cases of such metamaterial designs presented in literatures are investigated using the proposed method. First, numerical simulations of the three metamaterial designs are performed to extract the device parameters across the frequency spectrum and the results are compared with the reported results. Then, we investigate the refractive index discontinuity geometrically using a numerical simulation of a prism consists of the metamaterial unit cell excited by an electromagnetic plane wave. The prism simulation will allow us to confirm the refractive index discontinuity by observing the electromagnetic wave propagation at the output of the prism across the frequency spectrum of interest and determine whether the refractive index become negative at the discontinuity. Finally, the phase of an incident electromagnetic wave across the metamaterial are observed at the frequencies where the refractive index crosses over into the negative region at the discontinuities to investigate the physical behavior of the wave within and outside the boundary of the metamaterial.

For a given use case of a collaborative assembly station, a gripper is needed that can handle workpieces with varying geometries. Existing electric robotic grippers are heavy and expensive, while pneumatic alternatives are noisy, inefficient and need stiff tubes and additional valves. A gripper driven by shape memory alloys (SMA) is by design silent and lightweight, purely electric, can be controlled in an energy efficient way and is predestined for collaborative applications due to the soft actuator behavior. The challenges of the development of such a system are given by the requirements for the use case at hand. They are jaw opening stroke and high forces combined with a short cycle time. In this paper the design process of a normally closed parallel gripper prototype driven by SMA wires featuring 14 N maximum gripping force and 30 mm opening stroke is discussed. Thin NiTi wires with a diameter of 76 μm are used to ensure a fast cooling. With this measure a cycle time of 1 second and below can be reached. A two-stage telescopic mechanism having overall 96 wires in parallel drives the gripper jaws by means of a lever mechanics. The power consumption is around 48 W and the gripper is designed to work with the electrical industry low voltage standard of 24 V and 2 A.

State-of-the-art research shows that an increase in relative grain size in Cu-Al-Mn SMA leads to improved damping and SME performance. Building on that knowledge, the authors of this paper seek to understand if it is possible to exploit these improvements within a Cu-Al-Mn alloy, specifically, in the form of thin sheets. A series of thermomechanical treatments were applied to as-cast ingots of a Cu-Al-Mn shape memory alloy with the goal of obtaining thin sheets characterized by a high value of relative grain size. Additionally, samples of Cu-Al-Mn sheets were subjected to tensile cycling for the purpose of SMA “training”. Through optical microscopy, the authors of this paper investigated the effects of the applied treatments on the alloy structure. Furthermore, the phase transformation and damping behavior were studied using dynamic mechanical analysis (DMA). Methodology and preliminary results are presented in this paper.

In this study, we developed a lane detection and motion-blur compensation system for curved tunnel inspection by combining elements from art discipline (silk printing), and a camera, aiming to improve the accuracy of the self-positioning method in tunnel. We proposed an accurate and convenient printing method that is based on silkscreen printing using retroreflective paint and developed a method for creating barcode markers that can be printed on the surface of concrete. Here, we propose an extension of the aforementioned study where different curvature angles are considered, revealing that the reading of the marker is significantly affected by the lighting and shooting conditions. The results of this recognition experiment show that the method of using such a retroreflective marker to identify the position of the surface of curved structures may be used not only for vehicle tunnels, but also for human and animal tunnels, and for narrower and more curved tubular objects.

Small-scale magnetoactive soft robots (MSRs) with multimodal locomotion and wireless actuation capabilities have emerged in recent years for various highly sensitive and precise biomedical tasks such as targeted drug delivery and minimally invasive therapies. MSRs comprise magnetoactive elastomers consisting of micron-sized hard magnetic particles, such as neodymium-iron-boron (NdFeB), suspended or arranged into an elastomeric matrix. These robots generally exhibit large deformation under an applied magnetics stimulus, which is considered favorable for the aforementioned applications. Only limited efforts, however, have been reported on characterization of such robots. This is likely due to their nonlinear dynamics, especially under large deformations and hysteretic stress-strain characteristics, which strongly depend on the magnitude and frequency of the external magnetic stimuli. This study experimentally investigated and analyzed the real-time nonlinear and hysteretic responses of a MSR fabricated in the form of a cantilever beam made of a magnetoactive elastomer. An experiment was designed to characterize dynamic responses of the MSR under different magnetic stimuli at relatively higher frequencies to evaluate the rate-dependent hysteresis effect. A hardware-in-the-loop technique in conjunction with a PID controller was implemented, which permitted the generation of a precise and uniform magnetic field. The MSR was subjected to uniform magnetic loading perpendicular to the robot’s length leading to large amplitudes and rates of harmonic movements of the MSR. The experiments were performed under different intensities, ranging from 2 to 30 mT, at frequencies up to 3 Hz. The measured data were analyzed to obtain response time-histories and frequency response characteristics of the MSR, apart from the motion snapshots.

Intelligent textiles are predicted to see a surprising development in the future. The consequence of this revived interest has been the growth of automobile industry and the improvement of innovative methods for the incorporation of electrical and thermal features into textiles materials. In the present work, the development of a smart stretchable heating device integrated into a car-seat headrest has been identified as a target application. The need for smart conductive materials is becoming increasingly apparent, but they still represent a great challenge for the heating textile area, particularly in additive manufacturing. Polymer-based composites reinforced with copper and carbon powders, attractive as advanced coatings, seems to be good solutions to this issue. Such composites are now acquainted as ideal materials for electronic device engineering and fabrication, thanks to their excellent electrical and thermal conductivities while maintaining suitable mechanical compliance. For easier process and integration, an extrusion 3D printer is employed to achieve thin films coated on the surface of the textile substrate. The developed heater device consists of two principal copper electrodes (so-called power bus), and one heating resistor made of carbon composites designed in different configurations. Finite element models (FEM) are developed to predict the heating behavior of the tested fabric substrates under different pattern suggestions. Experimental measurements via a thermal camera are in consistent with the numerical solutions. It is pointed out that the design optimization based on an adequate tuning of the pattern’s parameters allows to solve inevitable matters in terms of temperature regularity and overheating effect.

Application of laser cutting operations on thin sheets of Cu-Al-Mn shape memory alloys can be used for shaping, or for producing different types of holes and hole patterns within the SMA sheets. In this paper, the authors evaluate the effects of laser cutting under different process parameters on the phase and chemical composition in Cu-Al-Mn sheet samples. The effects are observed using optical and scanning electron microscopy (OM and SEM), energy-dispersive x-ray spectroscopy (EDS), and differential scanning calorimetry (DSC).

Microwave vacuum drying (MVD) as a novel and advanced drying technology is wildly applied in the agri-food, pharmaceutical, and electronics industry, etc. However, achieving in-situ analyses of the realtime moisture content (MC) of products during MVD is still a huge challenge. This research aims to build an intelligent dehydration system by integrating a Terahertz time-domain spectroscopy (THz- TDS) into an MVD system to achieve in-situ monitoring of real-time moisture content (MC) in agrifood products. During dehydration, the THz-TDS continuality captured the spectra from a polyethene (PE) air hose containing the exhaust water vapor from the glass desiccator. Chemometric analysis of Gaussian process regression was applied to correlate the real-time MC loss of products with the corresponding numerical integration of THz absorption coefficients of vapor. The real-time MC content was accurately calculated based on the prediction. The result shows that the THz-TDS is able to sense the dynamic vapor changes within the MVD system by penetrating the PE air hose, and the established intelligent dehydration system combined with chemometric analyses achieved a satisfied MC loss and MC prediction, with R2 of 0.95 and 0.98, and RMSE of 0.002 and 0.031, respectively. The THz-TDS technique shows great potential to be integrated into an MVD system to achieve in-situ real-time MC evaluation, optimize dehydration condition, and predict the dehydration endpoint. The established intelligent dehydration system also provides a novel sensing strategy using THz-TDS to monitor the gas exchange within a closed system by penetrating a PE air hose in the system, and further widen the application of THz-TDS in the agri-food industry.

We have developed a wireless sensor node (WSN) powered by a piezoelectric vibration energy harvester that enables transmission of three-axis acceleration waveform data. Unlike a conventional WSN, which sends a single point representing the root mean square acceleration value, the proposed WSN allows the frequency, vibrational modes, and displacement of the target structure to be obtained. Therefore, this waveform-sending scenario is highly suitable for structural health monitoring applications. We used a power gating technique to reduce the standby energy consumption significantly and thus realize the waveform-sending concept. The overall dimensions and mass of the WSN are 3×3×3 cm³ and 26 g, respectively. The overall dimensions of the harvester are 5.6×2×2.1 cm3. The WSN measures the threeaxis acceleration of the structure’s vibration for 1.2 s at a sampling rate of 3,200 samples every 5 min, transmits the data, and then goes into standby mode. Because of the power gating technique, the energy consumption per cycle is as low as 108 mJ. We evaluated the WSN under both harmonic and random vibration conditions. For harmonic vibrations, the acceleration magnitude applied using a shaker was 1 m/s² at the harvester’s resonance. For random vibrations, a power spectral density (PSD) of 0.1 (m/s²)²/Hz and a frequency range of 10–100 Hz were set. The WSN operated successfully using only energy generated by the harvester and the transmitted waveforms matched the waveforms measured by a high-precision acceleration pick-up. Here, we report the WSN design methodology and the detailed charging characteristics of the energy storage capacitor.

A self-powered SECE (synchronized electric charge extraction)-based energy sensor is developed and applied to measuring shaft torque. The design is based on the setup of two-point magnetic plucking allowing the torque-induced phase angles between two pairs of magnets. The result shows the realization of broadband energy harvesting due to inducing mixed resonant modes of vibration from frequency up-conversion and enhancement by SECE. In addition, torque sensing is achieved by measuring the variation of modal amplitude of voltage response against the phase shift angles. For the case of torque sensing operated at the second resonant mode, the phase angle against the voltage is multi-valued. A solution for the unique sensing is to develop a CNN (convolution neural network) classifier capable of distinguishing various voltage waveforms from different phase angles. The prediction agrees reasonably with experiment.

Recently, vibrational energy harvesting has been considered a promising alternative to batteries for powering microsystems for large wireless sensor network applications. However, ambient vibrations are below 100 Hz, while most machines and equipment operate relatively at high frequencies (more than 70 Hz). Herein, we propose a theoretical study to harvest energy from high frequencies using a frequency-down bistable piezoelectric energy harvester mechanism. We investigate the energy harvesting benefit in the down-conversion of a high-frequency signal to a low-frequency signal utilizing magnetic coupling. A high-frequency driving beam triggers a low-frequency generating beam. We use a spring-mass-damper equivalent model to understand the operation mechanism of the proposed piezoelectric vibration energy harvester. Based on the theoretical model, the static and dynamic effect of magnetic nonlinearity on the performance of the proposed piezoelectric vibration energy harvester is numerically analyzed. The targeted applications are the down-conversion and the filtering of high frequencies and mass sensing, particularly the harvester’s behavior for mass sensing applications.

The ceaseless quest to realize novel classes of functional materials has provided new road maps to material autonomy. Autonomous materials and structures offer advanced functionalities such as sensing, actuation, selfhealing, communication, and computing to create a sense–decide–respond loop. They have numerous applications in robotics, human-machine interfacing, micro/nano-electromechanical systems, and flexible electronics. During the past decades, tremendous effort has been made to push the development of autonomous materials and structures. This paper presents an overview of the recent progresses, challenges and futures trends in autonomous materials and structures. In the area of material autonomy, active multifunctional metamaterials appear to open enormous field of study. Their scalability is an important feature to create building blocks for multiscale autonomous structures. Thus, this review paper provides an insight into their developments and future trends. The foreseeable challenges are further discussed.

Vibration-based piezoelectric energy harvester (VPEH) has received significant interests in the last couple of decades. In recent years, more emphasis has been given to the understanding and modeling the effect of nonlinearities introduced by mechanical and electrical aspects of the system, while the nonlinearity induced by the piezoelectric material is usually ignored. However, it has been experimentally found that this material nonlinearity can have a significant effect on the system behavior even at low to moderate excitation level. This paper is motivated to consider this piezoelectric nonlinearity in the system model, and study how the nonlinearity affects the power characteristics of the system, most importantly, the power limit and electromechanical coupling. Through a harmonic balance analysis, an approximated model is developed from a nonlinear model proposed in the literature, and allows for deriving closed-form expressions of important power characteristics. The approximated model elucidates the effect of piezoelectric material nonlinearity, which is represented by a nonlinear damping term and a nonlinear stiffness term. It is revealed that the addition of piezoelectric material nonlinearity results in interesting power behaviors that are largely different from that of a VPEH without piezoelectric nonlinearity. For instance, the power limit is reduced by the nonlinear damping induced by the piezoelectric nonlinearity. In addition, the critical electrical coupling, also known as the minimum electromechanical coupling for the system to possible reach the power limit, increases with the base excitation. A strongly coupled VPEH with piezoelectric nonlinearity under low excitation could become weakly coupled under large excitation.

Energy from mechanical vibrations is prevalent in the ambient, which can be effectively harvested using triboelectric generators. However, the efficiency of the harvesters is limited by the narrow bandwidth. Herein, we propose combining Vibro-impact and magnetic nonlinearity for Polydimethylsiloxane-based triboelectric energy harvesters to extend the operation bandwidth and enhance the efficiency of the traditional triboelectric harvesters. Our harvester design consists of a cantilever beam with a tip magnet facing another fixed magnet at the same polarity, inducing a nonlinear magnetic repulsive force. The lower surface of the tip magnet acts as an upper electrode of a triboelectric harvester, while the lower electrode with attached Polydimethylsiloxane (PDMS) insulator. Under the effect of base excitation, the system can vibrate in monostable or bistable oscillations by varying the distance between the two magnets, causing an impact on the triboelectric electrodes, and an alternative electrical signal is generated at a wide range of frequencies. The harvester’s static and dynamic behaviors are investigated theoretically and experimentally validated at different separation distances between the two magnets. We achieved higher bandwidth by combining Vibro-impact with magnetic nonlinearity, and triboelectric energy harvesters show promising applications for future wireless sensor networks at wider operation frequency bandwidth.

The efficiency of the energy harvesters can be improved by increasing the harvester bandwidth. Towards this, we presented a Two-Degree of Freedom (2-DOF) Vibro-impact Triboelectric Energy Harvester by combining multi-modality and piecewise linearity of two close resonant frequencies. The harvester structure consists of a primary cantilever beam attached to a secondary cantilever beam through a tip mass. The secondary beam is attached in the opposite direction to the primary beam. The bottom surface of the secondary beam acts as an upper electrode of a triboelectric generator. A lower electrode with bonded Polydimethylsiloxane (PDMS) insulator is attached at some gap separation distance underneath the upper electrode to create an impact structure. When the system vibrates, an impact between the triboelectric layers generates an alternating electrical signal. A 2-DOF system with lumped parameter theoretical model was developed to extract the governing equations. The structure’s dynamic behavior at different excitation levels, separation distance, and surface charge density were investigated theoretically. As a result, we achieved a wider bandwidth for the designed energy harvester. The proposed harvester demonstrated an increase in the maximum output voltage by more than 300 percent, and 250 percent increase in the bandwidth, by changing the excitation level from 0.1g to 0.7g. The result of this study can pave the way for an efficient energy harvester that can scavenge ambient vibrations over a wide range of excitation frequencies.

Increasing the bandwidth of the vibration energy harvesters is one of the research emphases to maximize the energy harvested from the ambient. Here we design a Two-Degree of Freedom Vibro-impact Triboelectric energy harvester with a double-impact configuration, which combines multi-modality and piecewise linearity to improve the harvesting bandwidth of triboelectric energy harvesters. The harvester structure consists of primary and secondary cantilever beams with two integrated energy harvesters. The two beams are designed to operate at close natural frequencies, and under the effect of the impact, triboelectricity is generated, and the bandwidths of the resonators are combined to create a wide bandwidth. The double impact system is investigated numerically to examine the structure’s dynamic behavior at different excitation levels, separation distance, and surface charge density to extract an optimal parameter for achieving a wide combined bandwidth. The system demonstrates the capability of connecting multi-modality and piecewise linearity to significantly broaden the triboelectric energy harvester’s bandwidth.

In this paper, we design and experimentally validate a new auxetic nonlinear piezoelectric energy harvester for broad working bandwidth and high power output, which combines a clamped-clamped beam with multiple rotating square unit cells. On one hand, the key structural parameter of the square rotating unit cell is adjusted to obtain desired broad working bandwidth. On the other hand, the number of the unit cells is increased to improve the power output of the energy harvester with minor influence on the working bandwidth. Therefore, based on the parameter adjustment and unit cell number increment, the proposed energy harvester can obtain both broad working bandwidth and high power output, which can solve the trade-off between these two aspects in previous auxetic nonlinear energy harvesters. Finite element analysis is performed to analyse the characteristics of the energy harvester. The lumped parameter model is utilized to predict the performance of the energy harvester, which matches well with the experimental results. In the experimental validation, under 0.3g base acceleration, the working bandwidth and power output of the auxetic nonlinear energy harvester are increased by 14% and 268%, respectively, compared with the conventional nonlinear energy harvester.

Traffic signal support structures are slender, highly flexible, and lightly damped. Therefore, they are particularly susceptible to wind-induced vibrations, which result in repeated load stresses and fatigue failures. A tuned energy harvesting inerter damper (TEHID)is proposed to reduce wind-induced vibrations of traffic signal support structures and convert the wasted vibration energy into electricity. The TEHID creates a large inertia mass by converting the low-frequency vibration motion of the light head to a high-speed rotation thereby eliminating the need for a large physical mass and accommodation space required by the conventional tuned mass damper (TMD). This paper focuses on the nonlinear dynamics modeling of the wind-induced vibration control and energy harvesting system for traffic signal support structures. The traffic signal structure is modeled as an L-shaped beam with multi-segments and the TEHID is simplified as a three-element device consisting of a spring, a damper, and an inerter. The nonlinear equations and the boundary conditions governing the motion of the integrated vibration control and energy harvesting system are derived from the energy method and presented herein. Modal analysis is conducted and the derived natural frequencies and mode shapes are compared with the finite element simulation results to validate the analytical model.

The purpose of this study is to discuss the possibility of the concept of physical reservoir computing (PRC) in the field of structural health monitoring (SHM). PRC is a physical realization of a class of recurrent neural networks called reservoir computing (RC). This consists of an input layer, mutually connected network of neurons with strong nonlinearity with fixed coupling weights (referred to as reservoir), and an output layer with learnable weights. The key idea of PRC is to replace the reservoir part in RC by a specific physical entity, which has opened new possibilities of smart structures by providing a way to embed some sort of intelligence in structures. In this study, we propose to apply this framework to SHM by regarding the target structure itself as the physical reservoir. Unlike the conventional problem setting in PRC, our purpose is to detect the change occurred in the physical reservoir due to structural failure. In this paper, we propose one possible methodology to achieve this, in which the output layer is trained to learn some nonlinear function so that the increase of the error may indicate the change of the reservoir due to failure. A simple toy problem using a network of interconnected nonlinear oscillators are presented to examine the validity of the proposed method.

The purpose of this research is to measure the free-decay dynamics of a magnetorheological (MR) sandwich beam when influenced by a semi-active magnetic field and comparing the resulting damping performance to those of baseline fields. The research effort involved an experiment where the beam freely decayed while in a magnetic field that influences the MR sandwich beam, altering its damping performance. In addition to baseline cases of no magnetic field or a constant field, the electromagnet also had a field that would shut off after a set time and a field that would switch between a high and low field strength at a certain frequency. These results were also recreated numerically, which required an experimental modal analysis to gather certain material property data. The experimental findings showed little variation in the damping performance regardless of the magnetic field used, while the numerical analysis indicate that the magnetic fields would quicken damping, but only slightly. The results suggest that improvements to the sandwich beam structure may yield the greatest improvement in MR-fluid-based damping performance.

The article presents a novel MISO (multi-input-single-output) diagnostic system suitable for spatial condition monitoring of bearing/gearbox instruments with multi-location defects. The sensor array consists of three piezoelectric patches: one is attached to the surface of the bearing house and the other two connected in parallel are mounted on the wall of the planetary gear. These two sets of patches are electrically connected in series for sensing the fault signals whose sources of anomalies come from either the bearing or the gear. They offer an advantage of allowing a single voltage output from multiple inputs. In addition, two inductances are connected to the sensor array to form LC resonant circuits for filtering the irrelevant noise at high frequency. A convolutional neural network (CNN) classifier is trained by 12x150 FFT spectrums. The result from the testing data with 12x10 FFT spectrums shows that the average accuracy is achieved to be as high as 92:5%, confirming the soundness of the proposed model.

An essentially nonlinear digitally programmable shunt circuit is explored in this work for the practical realization of nonlinear energy sink (NES) behavior in piezoelectric structures. The NES allows for energy transfer from the host structure to the nonlinear attachment in an irreversible fashion as well established. The main advantage of a NES is its ability to absorb vibrations over a broad frequency bandwidth since it has no preferential resonance, i.e., it is not tuned to any specific linear resonance frequency. In this work, a synthetic impedance circuit is employed for the emulation of a nonlinear inductor connected in parallel to a resistor, providing digital analogous of essential stiffness nonlinearity and damping, respectively, while piezoelectric capacitance acts as the mass analogue. Model simulations are conducted first to identify the suitable parameters of the synthetic impedance circuit in order to guide the experiments. The performance of the piezoelectric NES is then validated experimentally for a geometrically linear piezoelectric cantilever shunted to a programmable essentially nonlinear inductance circuit. Unlike the analog circuit explored in the literature using nonlinear capacitance (hence requiring negative capacitance in the circuit to make it essentially nonlinear), this work is inductive type (does not require negative capacitance) and is entirely programmable with digital control.

High-rate time series forecasting has applications in the domain of high-rate structural health monitoring and control. Hypersonic vehicles and space infrastructure are examples of structural systems that would benefit from time series forecasting on temporal data, including oscillations of control surfaces or structural response to an impact. This paper reports on the development of a software-hardware methodology for the deterministic and low-latency time series forecasting of structural vibrations. The proposed methodology is a software-hardware co-design of a fast Fourier transform (FFT) approach to time series forecasting. The FFT-based technique is implemented in a variable-length sequence configuration. The data is first de-trended, after which the time series data is translated to the frequency domain, and frequency, amplitude, and phase measurements are acquired. Next, a subset of frequency components is collected, translated back to the time domain, recombined, and the data's trend is recovered. Finally, the recombined signals are propagated into the future to the chosen forecasting horizon. The developed methodology achieves fully deterministic timing by being implemented on a Field Programmable Gate Array (FPGA). The developed methodology is experimentally validated on a Kintex-7 70T FPGA using structural vibration data obtained from a test structure with varying levels of nonstationarities. Results demonstrate that the system is capable of forecasting time series data 1 millisecond into the future. Four data acquisition sampling rates from 128 to 25600 S/s are investigated and compared. Results show that for the current hardware (Kintex-7 70T), only data sampled at 512 S/s is viable for real-time time series forecasting with a total system latency of 39.05 μs in restoring signal. In totality, this research showed that for the considered FFT-based time series algorithm the fine-tuning of hyperparameters for a specific sampling rate means that the usefulness of the algorithm is limited to a signal that does not shift considerably from the frequency information of the original signal. FPGA resource utilization, timing constraints of various aspects of the methodology, and the algorithm accuracy and limitations concerning different data are discussed.

Membrane technology is one of the most reliable and efficient separation processes for water treatment. However, one of the main limiting factors in the membrane filtration process is fouling, which is the deposition or adsorption of contaminants on the membrane surface or inside the membrane pores. In this paper, induced-vibrations is proposed as a cleaning-aid by preventing and reducing membrane fouling. The response of the membrane to periodic displacement at its boundaries is found mathematically and experiments are performed using a tabletop shaker to verify the model. Humic Acid (HA), a common water foulant in filtration systems, are distributed on the surface and their motion is observed at various forcing frequencies. Here we aim to utilize induced vibrations to excite the membrane’s resonances and take advantage of the spatial non-uniformity of the resulting mode shapes. In these modes, there will be regions of the membrane which vibrate out-of-phase with one another, potentially reducing the deposition of particles on the membrane surface (fouling) further by creating instability in the fluid near the membrane surface. Because the amplitude of vibration varies across the membrane surface, the deposition of foulants will also occur unevenly. These uneven patterns of fouling may be able to be removed from the membrane more easily during subsequent cleaning.

This paper studies the use of a new Tuned Mass Multi-Sliding Friction Damper (TMMSFD) to increase the damping capacity of seismic isolators installed on a two-story base-isolated building to limit their lateral deformations. The proposed TMMSFD consists of a set of several masses that are laterally attached to the superstructure floor through linear springs. These masses are placed on top of each other one by one and are allowed to slide with respect to each other during the earthquake. The bottom mass that carries the weight of upper masses is in contact with the superstructure floor. The damping of system is supplied by the friction generated along the sliding friction surfaces. The TMMSFD has a low cost of installation, operation, and maintenance compared to common TMDs that use viscous fluid dampers for energy dissipation. The mechanical model of TMMSFD is installed on the numerical model of a two-story base-isolated building equipped with elastomeric rubber bearings in order to evaluate its performance in limiting the displacement of base floor. These models are created by the OpenSEESPy package which is a Python 3 interpreter of OpenSEES. A parametric study is performed to obtain the optimum design parameters of the TMMSFD including its total mass, frequency, and static friction coefficients of the siding surfaces for energy dissipation. The results of time-history analysis of numerical model show that the TMMSFD is capable of limiting the displacement of base floor with a little amount of friction implying its potential as a cost-effective tool for seismic protection.

The SALUTE project aims at evaluating performance of electroacoustic metasurface, employing a surface array of controlled electroacoustic actuators, for smart acoustic lining under grazing turbulent flow to be used in UHBR Technologies Engines. Theoretical and numerical investigations have been carried out for designing innovative concepts for complex aero-acoustic characterization in an engine mock-up. A specific focus was placed in the realization of prototypes for evaluating the metacomposite liner performances in 3D liners close to real engine implementation, its process complexity and robustness. This project provides new tools for designing smart acoustic liners; while acoustical experimental tests demonstrate efficiency and robustness of such technology for controlling UHBR noise emission. This paper presents the concept development from theory to technological realization and characterization by produced numerical tools. The experimental results obtained with the liners in acoustic flow duct facilities (FDF) have been realized in the PHARE facilities of Ecole Centrale de Lyon. Different configurations of liners have been tested using similar flow conditions as in target engine: 1 passive liner used as reference and a 3D active liner based on an array of electroacoustic absorbers. The final tests campaign comprises acoustics and aerodynamics measurements to characterize the aeroacoustics flow conditions, the membrane behavior, the achieved synthetic acoustic impedance and the resulting insertion loss.

This paper, originally published on 28 April 2023, was withdrawn on 2 October 2023 per author request.

This contribution focuses on innovative acoustic liner concepts for reducing noise transmission through acoustic waveguides. The technology employed to implement such innovative boundary treatments are electro-active acoustic absorbers making use of loudspeakers (as actuators) and microphones (as sensors). Its most ambitious application is in the nacelle of the new generation of Ultra-High-By-Pass-Ratio (UHBPR) turbofans. In particular, this work targets higher modal-order sound fields (such as the ones in the UHBPR in the frequencies of interest). A nonlocal boundary operator is presented to show the potentialities of programmable metasurfaces in overcoming the performances of classical liner technologies.

In this paper, the design, manufacturing and testing of a morphing winglet concept, developed in the framework of the Clean Sky 2 REG IADP AIRGREEN 2 Project is presented. Such an adaptive device is being developed by CIRA and manufactured by TECNAM to enhance wing aerodynamic efficiency in off-design conditions and reduce maneuver loads. The concept is based on two individual (asynchronous) morphing surfaces consisting of two “finger-like” mechanisms driving the same number of moveable surfaces (the upper and lower tabs), controlled by dedicated electromechanical actuators.

In the present work, an overview is provided on the activities performed by CIRA, DLR and Univ of Bristol to develop and test a morphing system aimed at altering the twist of a blade to enhance the performance of the main rotor. The activities were performed within the research Project of “Shape Adaptive Blades for Rotorcraft Efficiency” (SABRE, H2020, 2017-2021), a Consortium constituted by six Partners (Univ. of Bristol – leader, Univs. of Munich, Delft and Swansea and the research centers of DLR and CIRA). Moving from the original features of the blade and the requirements of the reference rotorcraft, a layout of the architecture was sketched. A refined numerical model was then implemented to accurately predict the functionality of the concept and verify its safety compliance with the test facilities it was conceived for. Laboratory tests were thus performed on a dedicated prototype. Finally, on this basis, two other demonstrators were built and finally tested in the just mentioned wind tunnel and whirl tower plants.

In this paper an overview is given on some relevant activities performed by CIRA within the field of noise and vibration, guidance, monitoring and control. Conventional microphones, piezoelectric materials and fiber optics are the sensing strategies used for the proposed applications. High level of integrability, wide operational frequency range are just some features that make them particularly suited for noise and vibration, structural monitoring and sensing, micro actuation and harvesting. The first study regards an active headrest system developed for aircraft cabin seats based on the filtered- X LMS algorithm. Experiments carried out on a mock-up of active headrest are described along with noise attenuation results in a representative acoustic field. After that, a structural monitoring application is presented via strain gauges, piezoceramic sensors, and fiber optics. A series of drop tests are executed on a representative model of a flexible fuel tank, that is dropped from a certain height on an instrumented steel plate and equipped with such deformation sensors. Finally, guided elastic waves generated by piezoelectric transducers are investigated for de-icing purposes. The development of such a specific technology has required the assessment of a dedicated approach that is addressed in this paper, along with its level of maturation and possible future developments.

The bandgap generated in piezoelectric metamaterials with resonant shunt circuits unveils a great potential for vibration control. This paper presents a piezoelectric metamaterial with the capability of broadband vibration attenuation by adaptive bandgap tuning. Unlike the widely used synthetic impedance circuit, a self-tuning resonant shunt circuit by integrating a microcontroller-driven digital potentiometer into the synthetic inductor circuit is developed to achieve the bandgap adjustment of the piezoelectric metamaterial. Specifically, the excitation frequency is detected by the microcontroller, and the synthetic inductance in the resonant shunt circuit is adjusted in real-time based on a given criterion. An experimental study is conducted to demonstrate the dynamic behavior and vibration suppression performance of the developed piezoelectric metamaterial. The results confirm that the self-tuning resonant shunt circuit can rapidly respond to frequency-varying vibration sources and endow the piezoelectric metamaterial with an extremely wide vibration attenuation region.

Acoustic energy transfer (AET) is considered to be a promising technology without electromagnetic interference and safety issue compared to other wireless power transfer methods, especially for biomedical applications. In this paper, an AET system using piezoelectric transducers is modelled by equivalent circuit representation and finite element method, which in general give consistent results. A parametric study is then conducted to understand the influence of the sizes of barrier and piezoelectric transducers as well as the load resistance on the performance of the AET system. It is found that the area of the barrier has negligible impact on the performance, but the thickness of the barrier does, and the thinner barrier is favorable. In addition, it is found that a transfer efficiency of over 90% can be achieved if the transducers are optimized with thickness of 1.8-2.0 mm and the diameter of 24 to 26 mm. As the load resistance increases from 5 Ω to 400 Ω, the maximum efficiency of about 90% is achieved with a medium load resistance. These findings provide useful guidelines for AET system design.

This study proposes a multifunctional, thin membrane gel based on a formulation of PDMS and boron. The proposed gel offers a dynamic passive stimuli-responsive sound absorption at low frequencies, which can be transformed to active noise cancellation with the use of a secondary sound source. The passive behaviour of the proposed material is the result of a dynamic phase transition in the material’s polymeric network, activated by the interaction with the travelling sound pressure wave. The presence and extent of the phase transition in the material was investigated via Fourier transform infrared spectroscopy and oscillatory rheological measurements, where it was found that the amount of boron in the gel has a crucial role on the occurrence of the phase transition and consequently on its acoustic performance. The passive scenario results revealed a high and dynamic absorption of approximately 80% at the absorption coefficient peaks, which dynamically shifted to lower frequencies while sound amplitudes were increased. The active noise cancellation was successfully demonstrated at the lower frequencies range, as the occurrence of the phase transition was actively controlled via the sound pressure wave introduced. The aforementioned phase transition was intensified, with energy consumed in this process, resulting in a dynamic noise cancellation. These results demonstrated that the proposed gel membrane material can be used to develop active/passive deep subwavelength absorbers with unique properties, which can dynamically tune their performance in response to external stimuli, and that can be further controlled/activated with the use of mechanical transducers.

In this study, we develop a method to analyze traveling waves generated by two bending modes of a two-dimensional piezoelectric actuator. This actuator has a composite structure constructed by a stainless-steel plate and piezoelectric PZT sheets. A developed analytical model analyzed the characteristics and efficiency of the traveling waves generated by the superposition of different bending modes. Using the multi-integer frequency, two-mode (MIF-TM) driving method, a steady traveling wave can be generated using two driving frequencies with an integer multiple relationships and near two bending modes. The optimization of the driving parameters is conducted by developing a cost function using the Hilbert transform, in which the driving voltages and the phase difference between the two driving frequencies are used. Finally, this analysis method is verified by using the finite element method.

The purpose of this study is to develop a novel concept of smart structural systems that can recognize their own structural integrity by an embodied high density sensor network. Over the past two decades, sensor networks for automatic inspection application have been intensively investigated, and it has now become reasonable to deploy over 1000 sensor nodes in a single structural system. It would be certain, however, that the current approaches that require rich electronics and wireless communication at each sensor node will reach its limit due to huge amount of data overwhelming the network capacity and centralized computing resources. In this study, we propose a new approach to make a breakthrough in both communication and computation for such high density sensor networks of the next generation. In our approach, a number of sensor nodes with simple functions are embedded in the structure, each of which reacts to the elastic waves propagating through the structure by applying a force to the structure after a simple nonlinear transformation. This allows the whole nodes to be mutually coupled through the medium of elastic waves, forming a neural network that incorporates the dynamic characteristics of the structure as the coupling weights. In this paper, we present a possible realization of our concept with basic formulations, and present numerical simulations to examine how the proposed network behaves under a single frequency input. It is presented that the network exhibits a bifurcation in its asymptotic behavior from modulated response to steady-state depending on the structural conditions.

Actuators regulate motion in manufacturing and industrial automation by applying an excitation force or torque. Conventional actuators do have their advantages; however, they have multiple components (prone to wear and tear), are expensive during maintenance, bulky, and suffer from backlashes. Therefore, smart-material-based actuators have been increasingly proposed to overcome such shortcomings. Shape memory alloy (SMA) is generally considered for such applications due to its high power-to-weight ratio, noise-free, energy-efficient operation, and facilitating miniaturization. The current research exploits the advantages of the pennate musculature with the properties of SMA to develop a bipennate SMA-based rotary actuator. Pennate muscle fibers are aligned obliquely to the muscle line of action, enabling fiber force to be coupled to macro-level muscle force, resulting in increased force output. The study presents an ergonomic-design-integration-framework of an SMA-driven rotary actuator. The lightweight gearless actuator has drivability without backlash, compatible with a rhombus-based-compliant power transmission system. An analytical model of the bipennate SMA-based rotary actuator has been developed and experimentally validated. The new actuator delivers at least twice the actuation torque (2.1 N-m) compared to the SMA-based rotary actuators reported in the literature. The actuator also delivers a high associated angular displacement ranging from 60°-70°. The actuator design parameters have been optimized by implementing a constrained gradient descent algorithm such that the output torque, stroke, and efficiency of the actuator system can be tailored as per the requirement and application. The actuator has varied applications, from healthcare devices to next-generation space robots.

Piezoelectric rotary motors have become the standard motor for rotational motorization. However, due to its complex structure and operational mechanism, its cost is considerably high. To reduce the complexity and cost of piezoelectric rotary motors, we developed a new type of motor driven by traveling waves. It is constructed of a rectangular stainlesssteel plate and four piezoelectric actuators. To generate a rotational traveling wave on a rectangular plate, two higherorder bending modes are stimulated to generate rotational traveling waves propagating in a diamond-shaped trajectory. The dimension of the stainless-steel plate and four piezoelectric PZT plates attached to its surface. The boundary conditions are chosen to be simply supported in the x-direction and free-edge in the y-direction, and an analytical model is derived for analyzing its vibration profile. To stimulate the rotational traveling waves, the Φ34 and Φ43 bending modes are chosen. The dimension of the stainless-steel plate was designed, and the resonant frequencies are close to each other at 2.733kHz and 2.781kHz. Using this design, both bending modes are simultaneously excited with a single driving frequency at 2.757kHz. The combined Φ34 and Φ43 bending modes became a steady rotary traveling wave, and it can be used to drive a rotary starter. It is also found that the vibration performance could be optimized by modulating the phase difference and voltage ratio between the Φ34 and Φ43 bending modes. Finally, the driving method of this piezoelectric rotary motor is experimentally verified and compared with the analytical model.

The aim of this study is to develop a self-propelled, two-dimensional rotary piezoelectric plate actuator driven by a superposition of bending modes. It is achieved by generating two opposite-direction traveling waves on a thin rectangular plate. The structure design of this rotational actuator was simple and a cost-effective. The structure was composed of a 50mm*41mm*0.5mm stainless steel plate and two 50mm*20mm*0.2mm piezoelectric PZTs sheets attached to its surface. The boundary conditions were simply supported in the x-direction and free ends in the y-direction. To generate traveling waves in opposite directions in the x and y directions, mode 12, mode 21, and mode 22 bending modes were chosen using a multi-integer frequency, two-mode driving method (MIF-TM). An analytical solution was derived to optimize the driving efficiency. The Hilbert transform is also applied to identify the optimal driving parameters. It is demonstrated that traveling waves in opposite directions can be generated. Mathematical modeling and experimental studies are both detailed in this paper.

The ability of a piezoelectric actuator in energy conversion is rapidly expanding in several applications. Some of these applications for which an ultrasound piezoelectric actuator can be used are surface cleaning, metal cutting and welding, and biomedical applications such as needleless drug delivery. A new application of piezoelectric actuators is the Avionic Deicing System. The working frequency of actuator is between 100 kHz and 150 kHz, depending on temperature and ice thickness, and output power levels at several hundreds of Watts. The power supply of piezoelectric actuators has to provide an output voltage of up to 200 VAC at the resonance frequency with low consumption. This article discusses and analyzes a low-consumption electromechanical deicing solution based on piezoelectric actuators, its operating principle, and its driving power supply development supported by experimentations on the setup representative of a part of the Nacelle.

With smaller, cheaper, and more energy-efficient electrical components, energy harvesting systems have been a more attractive source of energy supply for wireless sensors, transducers, and other devices. One great example of mostly unused energy is the vibration of industrial machines. Along with the rise of predictive maintenance, more wireless sensors have been used to monitor those machines. Where the vibration energy present in those machines can be used to extend the sensor’s life constrained by the battery. This work presents two fabrication approaches to design these devices using the piezoelectric principle: MEMS fabrication and micro-machined devices. MEMS are widely investigated for harvesting purposes for their capability of building complex microscale structures (< 0.1 cm³). However, it can be difficult to designing MEMS energy harvesting systems for the low frequency range (40 Hz to 200 Hz), which is the operating range for standard industrial machines. The adapted micro-machined harvesters from off-the-shelf piezoelectric components mostly used in macro-scale applications (> 10 cm³), can be an alternative in this situation. Numerical models were developed to simulate the dynamic behavior of the piezoelectric device and used as input for design optimization. The models were improved using a differential evolution algorithm optimizing in terms of the Normalized Power Density (NPD) and Mechanical stress. In order to validate these models, prototypes were built ns tested, with the results compared considering the NPD and frequency bandwidth. The optimization process raised key design aspects of meso-scale low-frequency piezoelectric devices, including stress limits of thin-film piezoelectric and fabrication complexity, Overall, these aspects suggest that there is an advantage of micro-machined designs over MEMS devices for these applications.

The interest in modeling and prototyping the so-called Vibration Energy Harvesters (VEHs) has increased significantly in the last decades, given the growing demand for energy sources that can capture energy from the vibration of a machine, for example, to power small sensors and vibration monitoring devices. In this work, the design and optimization of a commercial Electromagnetic Vibration Energy Harvester (EMVEH) are presented. Such a device contains in its interior a resonant-type electromagnetic transducer, the latter composed basically by a seismic mass, a mechanical spring and a multi-turn coil. The complete set weighs about 90 g and occupies a total volume of approximately 50.97 cm³, being able to generate up 45mW at its resonance frequency of 60 Hz, with a bandwidth of 2.5 Hz. Furthermore, the linear generator presented in this paper reaches a maximum Normalized Power Density (NPD) of 1.8018mW/(cm³g²) at an acceleration amplitude of 0.7 g (∼ 6.67m/s²). To proceed with electromechanical modeling and further optimization, a numerical model was developed via commercial software COMSOL Multiphysics, from which it was possible to optimize its geometry in order to maximize its NPD and power output. A Surrogate optimization algorithm was then implemented in MATLAB, in which both volume and mechanical stress were considered as project constraints.

Since the significant growth of interest in soft robotics, artificial muscles and biomimetics, soft, capacitive dielectric elastomer sensors (DES) have been in the focus of development. However, when including a sensor into any device, tool or, for example, a machine element, there are several factors which have to be considered, e.g., the ease of embedding the sensor, the maintenance of the functionality of the machine element, as well as the quality of the embedded sensors and their reproducibility. In this work, we will focus on the quality of the sensor and present a procedure for manufacturing multi-layer capacitive strain sensors. In order to assess the influence of different manufacturing processes on the quality of capacitive DES, a variety of thin multi-layer sensors were fabricated. Furthermore, using an LCR meter, the equivalent electrical capacitances (C) at the two sensor contacts were measured. It is shown that C varies depending on the quality of the electrodes. By testing multi-layer DES (ML-DES) with an electrode diameter of d_electrode = 3 mm, with three and four electrode layers, a maximum capacitance of C₀ = 6.7 pF and C₀ = 10.5 pF was achieved for the undeformed sensor, respectively. The obtained capacitance values show that following the presented recommendations for creation the electrodes enables to improve the reproducibility and quality of the manufactured ML-DES. The fabricated sensor is soft and deformable due to the compliance of the elastomeric film used. Such a capacitive ML-DES can be used, for example, as a soft strain sensor implemented into the elastic element of a jaw coupling.