This PDF file contains the front matter associated with SPIE Proceedings Volume 12043 including the Title Page, Copyright information, and Table of Contents.

Thermomechanical couplings are responsible for the smart behavior of Shape Memory Polymers (SMPs). Additionally to the shape memory effect, the strong and fast glass transition in this kind of material is directly related to radical changes in the storage modulus and loss factor of the material. When integrated into composite structures, these materials can be used to change in real time the global stiffness and structural damping. This type of strategy opens new ways for vibration control which are currently investigated at FEMTO-ST institute. Several applications of this concept are described, corresponding to various scales and frequency ranges. For each of them, the design strategy based on finite element analysis is shown, taking advantage of thermomechanical couplings to describe the various behaviors of the composite. Then, the prototypes are manufactured and tested. Various complexity levels in the thermal fields are obtained through regulation, from homogeneous to gradient or even heterogeneous so that many structural behaviors can be obtained and changed in real time. Illustrations are shown on sandwich panels, phononic crystals and acoustic black holes. Open challenges are finally discussed.

This paper presents experimental and numerical investigations on the origami-patterned tube which is acknowledged as a promising energy-absorption device. Its buckling mode leads to high performances in terms of specific energy absorption (SEA) and crush force efficiency (CFE). The polygonal tube is prefolded by following an origami pattern, which is designed to act as geometric imperfection and mode inducer. First, a series of quasi-static crushing tests are performed on origami tubes with different materials and geometrical features. Specimens in SUS316L and AlSi10Mg are produced through Additive Manufacturing (AM). It allows to conveniently produce few samples with a complex shape. Finite Element Analysis (FEA) and Direct Image Correlation (DIC) are employed for a better insight into the complex crushing behaviour. The Aluminum tube shows a brittle behaviour while SUS316L tubes have extremely promising performance until local crack happens. Limits stemming from the employment of AM are explored and a new geometry is designed to avoid cracking. Second, a numerical design exploration study is carried out to assess the sensitivity of origami pattern features over the energy-absorption performance. ANSYS Autodyn is utilized as FE solver and DesignXplorer for correlation and optimization. The benefits of new patterns are investigated through geometrical optimization, and an improved geometry is proposed. The pattern stiffness is tuned to account for the external boundary conditions, resulting in a more uniform crushing behaviour. A similar force trend is maintained with a SEA increment of 51.7% due to a drastic weight reduction in areas with lower influence on post-buckling stiffness.

We present in this work a new semi-passive nonlinear absorber that aims to attenuate the vibrations of an elastic structure under external excitation. The design of the absorber consists of connecting a nonlinear shunt circuit to the host structure via a piezoelectric patch. The shunt circuit is composed of an R-L circuit connected in series with a quadratic nonlinear voltage source, intentionally added to the circuit. The main feature of this absorber is the replacement of the mechanical resonance by an antiresonance with an amplitude independent of the excitation level, and thus, a saturation phenomenon. This feature is a consequence of the two-to-one internal resonance generated by a specific tuning of the electrical resonance frequency. We show in this work the theoretical modeling of the absorber and experimental analysis on a cantilever beam structure in which the saturation phenomenon is detected, leading to a high attenuation level.

Methods and technologies to control the vibrations and noise on profiles excited dynamically by a fluid flow like vanes, rotor blades, or plane wings are tremendously needed. The following manuscript relies on a preliminary research proposing a vibration and noise control system integrated into the lower and upper profile of an outer guide vane prototype, consisting of five flush-mounted piezoelectric cells. To control the piezoelectric transducers, an impedance control circuit has been designed to dissociate current and voltage, and control directly their complex impedance as a frequency-dependent function. Then, the negative capacitance control principle is used to synthesize the controller as it avoids complex identification methods of the structure. Only by determining the optimal negative capacitance, it is possible to control the vibration level and acoustic transmission of the profile on a bandwidth around the main vibration mode of each cell. Hence, an average reduction level of −6dB is achieved on the vibration and acoustic transmission level for a large bandwidth around 3500Hz and 4500Hz, confirming the performance of negative capacitance control with the advantage of not needing the usual complex identification process of the structure model.

Laminated rubber bearing pad (LRBP) is widely used in small to medium-span highway bridges. They are directly placed between piers and girders to allow the bridge span to have horizontal movement and to transfer the gravity loads from decks to piers. Although LRBPs are not designed for seismic loads, their application can partially isolate the superstructure from the substructure keeping the piers intact during earthquake events. However, recent investigations indicate that large relative displacement between superstructure and substructure caused by sliding between girders and LRBPs can cause expansion joint or bridge span failure. As such, suitable restrainers should be implemented to control the potential large displacement. Among all types of restrainers, passive energy devices such as viscous dampers have shown a remarkable capacity in dissipating the earthquakes energy. This study aims at investigating the effectiveness of VD-LRBPs system, viscous dampers in conjunction with LRBPs, in controlling the large displacement between decks and piers. Accordingly, a 3D Nonlinear Time History Analysis (NTHA) was conducted on a case study RC bridge model under several earthquakes. OpenSees, an open sources finite element software, was used for the analysis. The relative displacements between decks and piers as well as the force in the piers, were recorded for two cases: 1- with only LRBPs and 2- with viscous dampers and LRBPs (VD-LRBP system). The results indicate that adding viscous dampers can reduce the relative displacement up to 60 percent. Also, it can reduce the potential residual displacement post-earthquakes to near zero.

In this work we investigate the transient dynamics of time modulated 2D spring-mass lattices. We show that a suitable temporal modulation of the stiffness parameters can be employed to functionally steer waves in the 2D space. This is accomplished by tailoring the group velocity profile associated with the unit lattice. We firstly derive the necessary modulation conditions to establish an adiabatic variation of the propagation direction for a wave packet, which allows for a reflection-free waveguiding. Then, we show a number of numerical examples to illustrate the limitations of such a strategy and how the performances are affected by non-adiabatic temporal modulations.

We propose a systematic way to achieve superfast edge-to-edge transformations in modulated mechanical lattices. According to the bulk-edge correspondence principle, the occurrence of localized edge states in dynamical systems is inherently linked with the topological characteristics of the band structure. Such states can be either localized at the left or the right boundary of the structure depending on a relevant modulation parameter which, in the case at hand, is the phase of the modulation. When the phase, or phason, is varied in an adiabatic fashion, there is the opportunity to trigger a modal transformation that drives the energy transfer between the boundaries of the lattice. We show that there is a limiting speed for this transformation to successfully occur and, given a number of damping and anti-damping elements placed along the lattice, we demonstrate that edge-to-edge transitions can be achieved with faster (non-adiabatic) propagation rates. This work opens new opportunities in the context of controllable waveguides and investigates the energy transfer capabilities of such a specific family of non-Hermitian structures.

Metamaterials have gained considerable attention in the past few decades due to their exceptional properties, such as negative mass, negative stiffness, and negative Poisson’s ratio. Much research has been conducted to understand how the band structure varies with unit cell designs for single and sandwich beam configurations. A few researchers have studied the variation in band structure in the graded metastructure considering single beam configuration. In this article, a new graded meta-sandwich beam has been studied that is constructed by repeating the unit cell, which consists of different combinations of translational and rotational springs. The band structure has been obtained by using the transfer matrix method along with Bloch-Floquet’s theorem. It has been noticed that a significant shifting and widening of the bandgaps has been noticed in the proposed graded meta-sandwich beam. Moreover, different configurations of metasandwich beams have also been studied. This study intends to provide the necessary physical insights to design a graded meta-sandwich beam for vibration attenuation applications.

Metamaterials have properties that are not usually found in conventional materials. Its unique periodic arrangement allows vibration suppression more successfully than most naturally occurring materials. In a Metamaterial beam, resonators with various designs can be attached in different configurations to obtain the bandgap according to the application requirement like vibration attenuation and waveguiding for aerospace, acoustics, or seismic isolators. This article proposes a cantilever beam with several spring-mass resonators periodically attached to it. The beam has been modelled as an Euler Bernoulli beam and is subjected to base excitation. The assumed modes method is employed to calculate the corresponding dynamic response of the structure in terms of its mode shapes. The transmissibility ratio is obtained as a function of the base excitation frequency. It is found that the transmissibility ratio is not only dependent on the excitation frequency but also the shape of the beam cross-section. Variation in the bandgap has been studied for different excitation frequencies and beam cross-sections, i.e., circular, triangular, rectangular and I-section, keeping the cross-sectional area and the mass of the beam constant. It has been observed that out of the four shapes, the I-section, rectangular and triangular or circular shapes are suitable for high, low, and intermediate frequency vibration attenuation, respectively. This study provides a basic framework to develop the metamaterial structures in an optimized manner.

This study reports numerical modeling of phononic-based crystals with the hourglass lattice periodically arranged in 2D space. The investigated resonant elements include dome shape metastructure as well as their various combinations, in particular, hourglass configurations. The mechanical wave band structure and transmission characteristics of such systems have been computed using finite element simulations performed in Comsol multiphysics. The general concept of a locally resonant phononic crystal is proposed. The concept utilizes elastic wave resonances to form constructive or destructive interference, which creates ranges of frequencies at which waves are either allowed to propagate (pass bands) or block in one (stop bands) or any direction (complete band gaps). The bandgap depends on the configuration of the periodic structure, the material of scattering unit, and that of a host matrix, which has been explored in this study. The unit cell consists of hourglass-shaped resonators repeated in two orthonormal directions, making it a 2D phononic meta material. The existence of a separate attenuation mechanism associated with the hourglass resonant elements that increase performance in the lower frequency regime has been identified. The results show formation of broadband gaps positioned significantly below the first Bragg frequency. The most optimal configuration is the crystal for low-frequency broadband attenuation, where each scattering unit is composed of multiple hourglass-based resonators. This system forms numerous gaps in the lower frequency regime, below Bragg bands, while maintaining a reduced crystal size viable for vibration isolation technology. The finding opens alternative perspectives for the construction of vibration mitigation in the low-frequency range, usually inaccessible by traditional means, including conventional phononic crystals.

Ultrasonic waves can be used to transfer power and data to low power electronic devices placed in inaccessible locations such as the human body, deep in the ocean, or in metallic enclosures. The upstream communication from the device can be transmitted using a minimal power by modulating the impedance of a piezoelectric transducer to switch between absorbing incident ultrasonic waves and completely reflecting it. The absorbed ultrasonic power in this configuration is supplied to an energy harvesting circuit for powering the device. Piezoelectric transducers are commonly optimized either for power applications only (narrow bandwidth and high sensitivity) or data applications only (broadband and low sensitivity). This work explores piezoelectric transducer design for simultaneous power and data transfer using acoustic and electrical impedance matching. A broadband transducer is designed to receive uninterrupted ultrasonic power at 1.3 MHz while transmitting upstream data at a different frequency band with a bandwidth of 300 kHz. The factors affecting power/signal reflection due to impedance mismatch are analyzed analytically, and an approach for simultaneous acoustic and electrical impedance matching is introduced to maximize the bandwidth and sensitivity. Several air-backed underwater transducers with different matching layers are fabricated, and their electrical and acoustic reflection as well as their electrical impedance are experimentally measured and compared to analytical predictions. A circuit for maximizing the bandwidth and sensitivity of the transducer for data transfer is then tested experimentally. Another circuit for achieving uninterrupted simultaneous power and data transfer using a single transducer is also implemented and tested.

Additive manufacturing of poly(vinylidene fluoride) (PVDF) as a piezoelectric material gained wide research interests over the past decade. Promoting the most polar β phase of PVDF during or after the printing process is the key focus to enhance its piezoelectricity. In this paper, a novel additive manufacturing technique termed precipitation printing is developed to produce high-β phase PVDF with the advantages of achieving geometry complexity and fabrication scalability, which is based on the different solubility of PVDF in two mutually miscible solvents. Through dispensing the PVDF/N,N-dimethylformamide (DMF) solution into a water bath, PVDF is continuously precipitated to form a solid structure while DMF diffuses into water. The β phase fraction of printed PVDF is improved to 64.2%. By further hot pressing of precipitation printed PVDF to reduce internal porosity, the piezoelectric d31 and d31 coefficients are measured to be 1.95 pC/N and -6.42 pC/N, respectively. Precipitation printing is also demonstrated to fabricate piezoelectric PVDF energy harvesters, such as a stretching mode strip energy harvester and a heel insole energy harvester. Therefore, precipitation printing provides a new additive manufacturing technique for producing high-β phase PVDF with strong piezoelectric effect, which can be potentially used to produce sensors, energy harvesters and actuators.

There is a clear need to power electronic components wirelessly. Various applications cannot be powered by wired or electromagnetic means. Acoustic energy transfer (AET) is an effective method in powering devices sealed or shielded by walls, and such applications are termed though-wall AET systems. These systems are constructed of a transmitter and a receiver that are bonded on opposite sides of the wall. Through-wall AET systems are typically modeled as three-layer systems. This method does not account for the additional layers created by the bonding agents that connect the transducers to the wall. Additionally, modeling of such systems assumes motion solely in the thickness direction. This assumption implies that the system undergoes “piston-like” deformation. This work addresses the need to computationally investigate through-wall AET systems and address the consequences of the aforementioned assumptions.

Low-frequency applications of piezoelectric shunt circuits for vibration and noise attenuation triggered the research on implementing synthetic impedance circuits in smart structures a few decades ago. Most of the existing efforts have been limited to standard scenarios of emulating linear circuit components such as inductances by means of their synthetic circuit counterparts to avoid the use of large coils when targeting relatively low frequencies. Other examples have included the emulation of negative capacitance circuits in various applications, most recently for bandgap enhancement in locally resonant piezoelectric metamaterials and metastructures. In this work, we explore synthetic impedance circuitry emulating nonlinear relationship to use in conjunction with piezoelectric structures, particularly for vibration absorption. The focus is placed on nonlinear inductance development to realize Duffing-like behavior in the synthetic impedance circuit when combined with piezoelectric capacitance and dissipative (resistive) elements. Time-domain numerical simulations, approximate analytical modeling, and series of experiments are performed for comparison. Results are demonstrated on a piezoelectric cantilever shunted to such nonlinear circuits with different nonlinear parameters and excited under mechanical base motion.

Owing to their shape morphing capabilities and biomimetic nature, tensegrity structures offer a lightweight, adaptable, alternative to classical truss structures. Tensegrities comprise a collection of axially loaded compressive members (bars or struts) stabilized by a network of tension members (strings or cables), resulting in flexible structures which can be pre-stressed and actively controlled to change their shape. In this research, we study the morphing capabilities of the cylindrical triplex tensegrity by actively changing the length of the structure’s internal cable network. A geometric approach is used to characterize the full range of statically equilibrated shapes of a cylindrical triplex tensegrity structure. Then, trajectories are designed from a subset of equilibrated shapes and implemented in open-loop on an experimental triplex structure.

Asymmetric carbon fiber reinforced composites have shown immense potentials in adaptive structure applications such as morphing airfoils,1–4 and energy harvesters.5 Due to the unidirectional prepregs used for their fabrication and strongly nonlinear behaviors, these composite laminates can show significantly different load-displacement responses along with different loading directions. Moreover, asymmetric composites can exhibit bistability, offering a pathway to easily switch between different mechanical responses. This paper presents two switchable structure concepts based on asymmetric composites. The first concept exploits two distinct responses in the [0°/90° ] laminates in two perpendicular in-plane directions. Via a simple snap-through, such structure can switch between stiff and compliant. Preliminary experiments show that it can achieve close to 70:1 stiffness ratio between these two configurations. The second concept is a Kresling origami structure fabricated in a novel way using asymmetric fiber composites and 3D-printed flexible TPU material. Due to the asymmetric layup in their triangular composite facets, the Kresling structure can switch from a “foldable” configuration to a “locked” configuration. Axial compression and tension response for foldable and locked configurations are experimentally investigated. These two case studies suggest that there are still many untapped potentials in the asymmetric fiber composites for advanced and multi-functional structural applications.

Adaptive load-bearing structures are expected to be an important part of future construction projects. Based on lightweight construction, engineering structures could be developed and implemented in an even more resource-efficient and multifaceted way by means of adaptive systems. Design, planning, and implementation of adaptive structures is multifaceted and combines different fields (civil engineering, mechanical engineering, computer science, electrical engineering, materials science, etc.), so that interdisciplinary collaboration between different disciplines will be essential. The goals of this collaboration would be to find answers to the civil engineering problems (and the related ecological and social issues) of our time. Adaptive structural systems offer a fundamental and important approach to addressing present problems such as climate change, resource scarcity, pollution, and constant population growth. The demand for sustainability, efficiency, and recyclability is an important consideration for our future built environment. There is a clear shift in the construction industry where sustainability, above all, is the driving factor of many decisions in the design process. Future investigations of dynamic influences and the development of new design concepts should provide the answer of how and where exactly forces act inside systems and how these systems can be turned into adaptive structures. In this paper I will give a basic overview about adaptive load-bearing structures. In the first part I will present some basic information and a short literature review. After this, I will show some results of my investigations of a two-spring system and stiffness adaption through variable springs.

The widely used Brinson model allows through experimental data to describe the behaviour of shape-memory-alloys (SMAs) in different condition of stress and operating temperature. The chief advantage of this one-dimensional constitutive behaviour model is in accounting for the existence of two forms of martensite within the alloy, twinned and detwinned. An internal variable approach that represents the martensitic fraction is introduced by the model and divided into the stress induced components and temperature induced component. And providing a uni-axial temperature-stress diagram clearly separating the regions of the three stable phases: austenite (A), twinned martensite (MT), and detwinned martensite (MD). The complete knowledge of the Brinson model allows to estimate the SMA behaviour in different conditions and to improve it according to specific tasks. In order to apply the model it is necessary to experimentally estimate the SMA material parameters These parameters include the Young’s moduli of each phase and critical transformation stresses, phase transformation temperatures as a function of stress level and thermal expansion coefficients of both austenite and martensite, as well as recoverable strain, both initial and after the alloy has been trained. While the Brinson model has been developed and validated for NiTi based alloys, the increasing interest aimed at Cu-based SMAs, mainly for their competitive price and relatively high performance, requires a validation of its extension to these materials. The paper focuses on a specific alloy of interest, Cu-16Al-10Mn (%at.), but results can be extended to different chemical compositions. The paper explores the opportunity to use experimental methods based on monotonic loading and unloading of the Cu-Al-Mn specimens, as well as thermal cycling under both zero and non-zero stress levels to estimate the parameters mentioned above. Furthermore, its goal was to ascertain whether any specificity intrinsic to the Cu-based alloy would require changes to the parameter estimation method or introduction of new parameters to the model to fully describe its behaviour.

Origami robots are becoming very popular due to their excellent morphing abilities and ease of manufacturing. The use of Shape Memory Materials (SMM) for actuation in such structures have not only been proven to make them robust and adaptable to different conditions but also to provide special capabilities. Particularly, Shape Memory Alloy (SMA) actuators has been used for the self-folding/deployment of smart structures. This study presents a FEA-based thermomechanical model which couples a torsional SMA actuator with a rigid host structure using Shape Memory Polymer (SMP). A specific technique is used for the solution convergence of a complex nonlinear model. After folding the structure to an initial rotation, the influence of SMP stiffness on a Shape Memory Effect (SME) activated rotational motion is investigated. Additionally, the influence of SMP on the global rotational stiffness of such inherently soft structures is studied. The model serves as a starting point for a FEA-based design approach of SMM-equipped singular origami structures and can be topologically optimized for specific applications.

The flexoelectric effect of solids is an electromechanical conversion mechanism that occurs in all dielectric materials, often together with other effects such as the piezoelectric. Currently, piezoelectric, electrodynamic and electrostatic conversion mechanisms are mostly used in actuators, some of them use dielectrics. The converse flexoelectric effect, has not yet been widely explored as an additional effect in these dielectric materials. A broad understanding of this effect could lead to new applications with a wider range of materials. In this paper, we attempt to determine the contribution of the converse flexoelectric effect in a lead zirconate titanate (PZT) piezoelectric soft ceramic. For this purpose, strongly varying electric fields were applied to capacitive electrode arrangements. The electrodes were deposited on one side of PZT-wafers (PIC151). Sinusoidal as well as pulsed voltage signals were applied to the electrodes. Doing so, the samples showed displacements in all three spatial directions. To separate the converse flexoelectric effect from the piezoelectric, displacements were measured at different temperatures between 20°C and 350°C i.e. even above the Curie temperature (T_c). The resulting deflection follows the electrical input signal at all temperatures. Because piezoelectric effects can be excluded above the Tc, another effect must be responsible for the displacement. The significant displacement of 30 to 40% in comparison to room temperature is attributed to the flexoelectric effect.

2-D lattice structures have gained significant attention in the last few decades. Extensive analytical and experimental studies have been conducted to determine the elastic properties of the lattice structures. Further, the variation in the elastic properties of the passive lattice structures by changing various dimensional parameters and geometry have also been studied. However, once manufactured, it is impossible to vary the elastic properties of these lattice structures. A few studies have been conducted to understand the modulation of the elastic properties in symmetric hybrid lattice structures. This article proposes a geometrically asymmetric hybrid lattice structure having piezoelectric material on the opposite faces (top and bottom) of the consecutive inclined cell walls, respectively. The closed-form expressions have been derived by considering a bottom-up approach neglecting the axial deformation of the cell walls. Young’s modulus has emerged to be a function of externally applied voltage, warranting control of the elastic properties of the structure even after manufacturing. In contrast, Poisson’s ratio is independent of externally applied voltage. The transition from negative to positive values for Young’s modulus has also been observed at specific cell angle values and externally applied voltage to stress ratio. This study intends to provide the basic framework for voltage-dependent elastic properties in asymmetric lattice structures for potential use in various futuristic multi-functional structural systems and devices across different length scales.

Wave energy has the largest reserves and widest distribution among blue energy sources. However, the conversion and utilization of ocean wave energy are challenging. In this work, we developed a contactseparation mode triboelectric nanogenerator (TENG) with a simple structure for harvesting wave energy and powering marine sensors and transmitters and performed detailed electrical characterization under controlled laboratory conditions. A prototype power management circuit (PMC) was implemented to improve the output performance of the TENG. The output from the PMC could charge up a storage capacitor for powering sensors and electronics. Eventually, the TENG was integrated within a water-proof enclosure and tested using a custom-built wave simulator to evaluate the device performance in a more representative scenario. The device sustainably powered up an array of 27 LEDs and was able to charge up a capacitor up to 1.8 V for driving an acoustic transmitter. The results demonstrate that TENG technology shows great promise in harvesting low-frequency ocean wave energy.

The power harvested by non-tunable fluidic energy harvesters such as piezoelectric cantilever beams in turbulent flow is significantly smaller than that of tunable harvesters whose natural frequency can be tuned to match the dominant flow frequency. Incorporating a tandem of beams allows the power output per beam to be improved in such cases due to the additional contribution of aerodynamic coupling. In this paper, we explore the effect of beam configuration and length, gap-to-width ratio, mean flow velocity and distance from the grid on the aerodynamic coupling-to-input ratio and electromechanical efficiency for two side-by-side beams subjected to turbulence generated by a fractal I, fractal square and a fractal cross grid patterns. We introduced the aerodynamic coupling-to-input ratio in an earlier paper as a means to measure the influence of the aerodynamic coupling on the energy conversion process. Our results show that the electromechanical efficiency and coupling-to-input ratio are larger for a shorter, stiffer beam tandem than longer, more flexible beams irrespective of the fractal grid used to generate the turbulence. Furthermore, we have found the aerodynamic coupling force to be a much larger percentage of the force applied to the beams for the fractal turbulence grid cases, especially the fractal I pattern, compared to a conventional rectangular grid.

In recent years, there have been increasing interests in energy harvesting from concurrent wind flow and base vibration, based on a recent realization that the two types of excitations are inseparable in many practical circumstances like bridges, ships, aircrafts, offshore infrastructures, etc. There are several ways to achieve wind-induced oscillations, i.e., aero-elasticities, such as galloping, vortex-induced-vibration (VIV), flutter, etc. However, the basic principles for these aero-elasticities are different. Since the principles of these aeroelastic instabilities are different, the performance and dynamic characteristics of different types of aeroelastic energy harvesters will also be different when subjected to combined wind and base vibration loadings. This work presents a comprehensive comparison study to evaluate and compare the performance of different types of aeroelastic energy harvesters with 2:1 internal resonance in concurrent wind and base vibration energy harvesting. We consider three types of 2DOF energy harvesters based on galloping, VIV and flutter aeroelasticity. All three harvesters are subjected to concurrent wind flow and base vibration. It is shown that the two-to-one internal resonance is effective for all three types of harvesters under concurrent loadings, capable to simultaneously widen the synchronization bandwidth and enhance the voltage level. In particular, with the galloping energy harvester, a 153% increase in voltage level and 6.8 times increase in the bandwidth width are achieved around the 1st resonance region.

Galloping-based piezoelectric energy harvesters (GPEH) connected with various interface circuits are usually analyzed by treating their advanced structures and circuits separately, and a general model is missing to gain insights at a system level. To tackle this issue, this paper proposes a unified framework that enables an integrated view of the physics of linear GPEHs in multiple domains at the system level. In addition, it elucidates the similarities and differences among power behaviors of GPEHs connected with various interface circuits. It is based on two major elements: an equivalent circuit representing the entire system, and an equivalent impedance representing the interface circuit. Firstly, the electromechanical system is linearized and modeled in the electrical domain by an equivalent self-excited circuit with a negative resistive element representing the external aerodynamic excitation, and a general load impedance representing the interface circuit. Then, a closed-form, analytical expression of the harvested power is obtained based on the Kirchhoff’s Voltage Law, from which the optimal load, maximum power, power limit, and critical electromechanical coupling (minimum coupling to reach the power limit) are determined. In this unified analysis, the exact type of energy harvesting interface circuit is not assumed. After that, the power characteristics of a GPEH connected with five representative interface circuits are analytically derived and discussed separately, by using the particular equivalent impedance of the interface circuit of interest. It is shown that they are subjected to the same power limit. However, the critical electromechanical coupling depends on the type of circuit.

This paper studies the use of an energy-regenerative tuned mass damper (ER-TMD) to (a) passively control the displacement of superstructure of a two-degree-of-freedom base-isolated building model equipped with elastomeric rubber bearings and (b) simultaneously generate electric energy that can be used to power conventional sensors installed on the building to monitor its response during an earthquake. The proposed passive ER-TMD is composed of two parts: mechanical and electrical. The mechanical part consists of a moving mass (i.e., TMD mass) attached to the base floor through a linear spring-damper system, and the electrical part consists of two large permanent magnets, a rectangular aircore copper coil, and a harvesting circuit designed to maximize the electric power outputted from the proposed ER-TMD. The total damping coefficient of ER-TMD, obtained by adding up the damping effects of the mechanical and electrical parts, is variable and depends on the amplitude of vibration during the earthquake. A parametric study is carried out to find the optimum damping coefficient of proposed ER-TMD. The numerical results show that the proposed ER-TMD can limit the displacement of superstructure to a safe level while it is capable of generating an average electric power about 0.5W which is large enough to power a conventional accelerometer when the building is subjected to an earthquake with the intensity similar to that of maximum considered earthquake (MCE) as defined by ASCE 7–10.

A finite element method to simulate energy harvesters, recently introduced by the authors, is applied to investigate the transient charging behavior of a strongly coupled bimorph piezoelectric vibration-based energy harvester for a harmonic and a shock-like triangular pulse excitation. The system simulation method is extended to allow for charging a capacitor and the standard and the synchronized switch harvesting on inductor (SSHI) circuits are considered. The simulation results show that the standard circuit is more efficient for the harmonic excitation, while the SSHI circuit is more efficient for the shock-like triangular excitation. The influence of different capacitors is discussed.

The article presents a novel idea for the fault diagnostics of the timing belt based on developing a piezoelectric energy sensor attached to the synchronized electric charge extraction (SECE) interface. The device is composed of a piezoelectric cantilever beam with a tip magnet impulsively excited by another small magnet attached on the surface of a moving timing belt. As a result, energy is harvested by frequency up-conversion mechanism operated under magnetic plucking. It is observed that the extent to which power harvested from the failing belt is higher than that from the healthy belt, giving rise to the basis for condition monitoring of the timing belt by detecting the output power. In addition, the analysis shows that the power sensitivity to the magnetic distance can be enhanced to 145% by the SECE interface circuit in comparison with the standard (STD) interface circuit. The consequence of it is that the SECE case exhibits a more accurate decision boundary determined by the logistic regression to classify the healthy and flawed states, as confirmed by the experiment.

Inerter is a new and effective way to provide an equivalent mass effect to enhance the vibration suppression efficiency while reduce the overall mass of vibration dampers. This study investigates the performance of a novel inerter-enhanced nonlinear energy sink for simultaneous vibration suppression and energy harvesting. The effects of the position of the inerter and other key parameters, including the inertance, secondary-to-primary mass ratio, electromechanical coupling strength, etc., on the performance of the proposed configurations are examined by numerical analysis. The intended configurations are shown to be effective for both broadband vibration control and energy harvesting.

Negative capacitance can lead to advantages in piezoelectric based passive vibration suppression system using inductive shunting. However, the optimal amplifier (op-amp) as the key component in the negative capacitance circuit consumes power, leading to additional power requirements to operate the system. In this research, we explore the development of a self-powered circuitry that integrates together inductive shunting for vibration suppression, piezoelectric energy harvesting, and negative capacitance. With careful analysis of the power consumption of negative capacitance, the output power of energy harvesting system, and the vibration suppression performance, we can identify a circuitry design that can take advantage of negative capacitance to enhance vibration suppression performance where the net power of the system remains to be positive. Our results are validated through experimental investigations.

This study proposes a super-elastic memory alloy re-centering damper device and investigates its performance in improving the response of steel frame structures subjected to multi-level seismic hazard. The proposed super-elastic memory alloy re-centering damper (SMARD) counts on high-performance shape memory alloy (SMA) bars for recentering capability and employs friction springs to augment its deformation capacity. An analytical model of sixstory steel special moment frame buildings with installed SMARDs is developed to determine the dynamic response of the building. Then, nonlinear response time history analyses are conducted to assess the behavior of controlled and uncontrolled buildings under 44 ground motion records. Results show that SMARDs can enormously mitigate the dynamic response of steel frame structures at different seismic hazard levels and, at the same time, enhance their postearthquake functionality.

Braced frames and roof trusses may interfere with functional spaces in multi-story, portal-framed structures. This research explores the application of a deployable mechanism as part of the structure to enhance the performance of multi-story buildings. The work presented herein involves simulation of a 3D, scaled-down, aluminum-framed, deployable truss roof-braced frame system. The authors propose this new structural system for prototype structures, incorporating actuator-controlled mechanisms for significant shape changes leading to a topology change. The resulting deployable structural system is sleeker, utilizing less space, material, and energy than traditional structural forms to resist lateral and gravity loads.

The goal of this paper is to explore the dynamics, namely, the damping, of a sandwich beam filled with magnetorheological (MR) fluid subject to different time-varying magnetic fields. The experimental portion of this research has a shaker generate vibrations in the beam before shutting off, measuring the beam’s deflection decaying. The numerical analysis is similarly conducted with an initial displacement. In either case, the decay is measured by fitting an envelope to the displacement and measuring the time it takes for the deflection to reach 5% of its initial value. These results indicate that certain transient fields have marginally less damping while also conserving electromagnet power output.

In this paper the suitability of active shape memory alloy hybrid composite (SMAHC) technology to realize an adaptive airfoil trailing edge is evaluated. The demonstrator component investigated highlights the potential of such concept as an extreme lightweight variant of a morphing trailing edge. The main challenges for successful implementation according to today´s typical requirements were identified. The investigation includes analysis and model based modification of an successfully flight tested concept for adaptive vortex generators,1 as well as the design and implementation of a demonstrator of a morphing trailing edge, and its experimental investigation in the laboratory.

To reduce installation space as well as weight, the use of shape memory alloys (SMA) is advantageous in the field of actuator technology. A big challenge using SMAs in for actuation is their high energy consumption due to Joule heating. To overcome this, an actuator system based on the agonist-antagonist principle, using SMA wire actuators was developed. Main advantage is the possibility of an energy-free holding of the position without the use of special locking components. A prototype made of CFRP and SMA wires was developed and built. The structure consists of a CFRP laminate on which SMA wires are anchored on the upper and lower side. This work also contents a simulation approach of the actuating structure in ABAQUS® using a simplified phenomenological model.

Heat-driven shape memory polymers (SMPs) can revert to a memorized geometry once they reach the phase-transformation temperature. This work merges the fused filament three-dimensional (3D) printing and nScrypt microdispensing to create morphing and flexible electronics that could result in innovations in antennas and sensors for biomedical and aerospace applications. Polyurethane and polylactide will first be printed simultaneously on a 3D printer to form SMPs. The thermomechanical properties of the printed SMPs will then be characterized for different TPU/PLA ratios. By nScrypt printing silver electrodes on the SMPs, a morphing antenna will eventually be prototyped and characterized.

In the global aerospace industry, the demand for small satellites to verify space science technology at low cost is recently increasing. However, the payload volume is limited due to the small size of the satellite, and it affects the payload size and mission performance. To overcome this limitation, the utilization of deployable structures in space structures is gaining attention. In this study, we propose an 8U CubeSat structure concept that can be separated into upper 4U and lower 4U in orbit. A flat-retractable truss structure, which has a compact storage volume and high stiffness compared to other deployable structures, is used for separation between upper and lower units. To confirm the feasibility of the proposed structural concept, a CubeSat structure prototype is manufactured. Imaginary optical payload is assumed to be mounted and the optical performance of this concept is theoretically analyzed. In addition, a membrane shield concept in the form of an origami-based Bellows patterned cylinder is designed to prevent the light disturbance and thermal deformation of the deployable structure. Finally, the unit-separable 8U CubeSat structure integrated with the shield structure was presented.

We demonstrate our striking vision towards developing a new generation of multifunctional concrete materials with unprecedented mechanical properties. The proposed “metamaterial concrete” is based on the integration of snapping metamaterial and concrete design concepts. We show how integrating the concrete mixture with auxetic polymer structures with snap-through buckling behavior results in creating a concrete material system with new functionalities. The developed proof-of-concept prototypes are experimentally tested to verify the efficient of the proposed concept. The results are in a reasonable agreement with the numerical simulations. We discuss the potential of the metamaterial concrete systems in revolutionizing the concrete construction via supplementing the inherent weaknesses of concrete in fatigue applications. The composite constituency of the metamaterial concrete shows levels of compressibility, while maintaining a high level of stiffness. The compressibility of this material reveals the future for a ductile concrete with significantly high flexural capacity and ability to absorb vibration without incurring any flaws.

Natural evolution has been a major source of inspiration for scientists for decades. Here, we aim to harness the power of natural evolution for automated design and discovery of novel forms of metastructures. In the proposed process, evolution takes place by randomly creating an initial population of metamaterial entities that will pass on their genetic material to their offspring through variation, reproduction and selection. The metamaterial configurations with desired response emerge during this evolutionary process. We deploy this process to design metamaterial artefacts assessed during evolution with respect to minimum Poisson’s ratio. The experimental properties of the evolved metamaterial systems are in an acceptable agreement with the theoretical values. With the growing interesting in metamaterials for various engineering applications, artificial evolution of metamaterials could open up new avenues towards more efficient and creative design of these systems.

Recently, acoustic/elastic metasurfaces have gained increasing research interests due to their ability to control waves with compact and lightweight structures. A metasurface is a thin layer in the host medium composed of an array of subwavelength-scaled patterns, which introduces an abrupt phase shift in the wave propagation path and tailors wavefront based on generalized Snell’s law. The existing metasurfaces mainly depend on the linear dynamic behavior of the structures, while their nonlinear features have not been studied extensively. A couple recent attempts have shown means of introducing nonlinearity in acoustic metasurface designs, resulting in nonlinear effects such as second-harmonic generation (SHG). However, these studies mainly focus on generating and maximizing the higher-order harmonics, while the phase modulation and wavefront tailoring capability are less explored. Our study advances the state of the art and proposes a novel acoustic metasurface design with locally resonant nonlinear elements in the form of curved beams. We explore the nonlinear phenomenon, specifically SHG, of the proposed system using both analytical and numerical frameworks. Our results show that the proposed nonlinear metasurface can achieve SHG in the transmitted acoustic wavefield, and simultaneously demultiplex for different frequency components (i.e., split the second-harmonic component from the fundamental frequency component) by steering them into different directions. This study presents new theoretical and numerical platforms to explore the amplitude-dependent behavior of acoustic metasurfaces, expands their wavefront tailoring capabilities and functionalities, and develops new potentials towards efficient technologies to manipulate acoustic waves.

We present numerical and experimental investigations on the dynamics of a piezoelectric metamaterial waveguide with unit cell shunt impedance that can be varied in both space and time in a fully programmable manner. A piezoelectric bimorph with 30 separately bonded pairs of piezoelectric patches (i.e. 30 unit cells) is connected to a fully programmable gate array (FPGA)-based synthetic impedance system with 32 individually addressable shunt circuits. Spatial impedance profiles are programmed and stored in memory on the FPGA, allowing the system to switch between impedances at very high frequencies, resulting in nearly smooth time-modulation at low modulation frequencies. The switching rate between the stored impedances is determined by a digital trigger and external pulse train, allowing the modulation frequency to be smoothly varied. Four separate triggers enable different modulation frequencies to be set across the waveguide, such that multifrequency modulation schemes can also be explored. In this way, the developed experimental platform is capable of smooth, multi-directional spatiotemporal modulation of circuit parameters. Experimental results are presented for various inductive spatiotemporal modulation schemes, investigating the effect of modulation amplitude and directional behavior of the waveguide (e.g. for non-reciprocal propagation). Scanning laser Doppler vibrometer (SLDV) measurements provide full-field characterization of the waveguide. Numerical and experimental results demonstrate non-reciprocal behavior in the modulated waveguide.

With advances in new technologies, researchers are attempting to develop the next generation of adaptive structures with intelligence directly embedded within their mechanical domain, the so-called mechano-intelligence. These attempts will enable mechanical systems to perform intelligent tasks, such as sensing the environment, changing geometries, making decisions, and executing computation in an even more proactive and autonomous manner, as compared to traditional mechatronic systems. However, there is no systematic foundation in constructing and integrating different aspects of mechano-intelligence. To advance the state of art, this research proposes to enhance the mechano-intelligence in adaptive structures through a machine learning framework called Physical Reservoir Computing (PRC). We show that a tunable modular metastructure can learn from its own wave dynamics and adaptively tune its own band structure via PRC. In other words, the metastructure can sense different input waves, make decisions and output appropriate control commands to alter its own wave characteristics without digital signal processors and controllers, i.e., achieve autonomous and integrated mechano-intelligence. Overall, this research provides a novel method to achieve intelligent and adaptive vibration/wave control based on the concepts of physical computing and learning and forms the basis for multi-faceted functional-relevant mechano-intelligence to be embedded in future adaptive structures and material systems.

Nonlinear metamaterials present wideband and multimode vibration attenuation features leveraged by mechanisms such as internal resonances, bifurcations, and chaos. Nonlinearities can be provided to a metamaterial through periodic modulation of nonlinear constitutive material laws, by inducing periodic geometry asymmetries, or by including nonlinear local forces. This paper investigates the effects of nonlinear electrical attachments on the vibration attenuation performance of a onedimensional piezoelectric metamaterial. We investigate the effects of negative capacitance circuits on the restoring function of the nonlinear piezoelectric unit cell, whose linear term (controlled by the negative capacitance) can be rendered either positive or negative, paving the way towards the realization of monostable or bistable electromechanical attachments. We show that a piezoelectric metamaterial with nonlinear attachments attains enhanced broadband capabilities brought by the negative capacitance circuits. Numerical time- and frequency-domain analyses elucidate the effects of the nonlinear electrical attachments on the vibration attenuation of an one-dimensional electroelastic metastructure, revealing multimode attenuation features and attenuation bands substantially wider than the ones provided by a linear electroelastic counterpart.

Acoustic metamaterials are composite materials exhibiting effective properties and acoustic behavior not found in traditional materials. Through periodic subwavelength resonant inclusions, acoustic metamaterials enable steering, cloaking, lensing, and frequency band control of acoustic waves. A common drawback of acoustic metamaterials is that the properties are limited to narrow frequency bands. Investigation of practical active and adaptable acoustic metamaterials is valuable in achieving wider operation frequency bands. In this work, we explore different geometric configurations for a cutaway plate metamaterial unit cell with the purpose of vibration suppression. Resonators cut directly in a thin uniform plate function as local resonators. We examine the wavenumber band structure seeking wide and low frequency band gaps in the vicinity of the resonant frequencies of the local resonators. Variations in the geometry of the unit cell are examined to obtain band gaps for broadband vibration suppression. Wave shapes of the unit cell associated with the band gaps are also examined to aid in the parametric design of the unit cell. Additionally, as a means of tuning stiffness of the local resonators we attach piezoelectric actuators to the cutaway resonators with the goal of increasing the bandwidth of the vibration suppression and enabling frequency tunability of the system.

Nowadays, vibration monitoring system (VMS) using machine learning has been increasingly used to predict rotor faults. However, a sufficient amount of fault data is harder to collect practically than the normal data, as a result, the imbalanced training data set can significantly affect the accuracy of the trained classifier. In this paper, we proposed a data augmentation approach that uses physics-based high-fidelity dynamics simulation as an alternative to acquiring practical fault data. The overall procedure includes: (1) The high-fidelity numerical simulation model reflecting the behavior of rotor to obtain the vibration signature of fault data; and, (2) data augmentation with the simulation fault data in conjunction with experimental normal and fault datasets. A fully connected Neural Network (FCNN) is applied to build the classification model that identifies rotor faults focusing on mass unbalance. The rotor system considered in this study consists of rigid discs, shaft, eccentric mass, and bearing housings. The numerical simulation model in this work considers high-fidelity physical behaviors such flexible multibody dynamics having centrifugal force and gyroscopic effects. Time domain data of the vertical and horizontal vibration responses of bearing housings are obtained from simulation and then FFT is applied to extract the main feature in frequency domain, which is the amplitude of the 1X harmonics of the vibration responses. The data augmentation is accomplished with frequency domain data both from simulation results and experimental acquisition. This approach can tackle data imbalance problem which is one of the most critical hurdles in neural net-based. fault diagnosis. From experimental verification, high accuracies more than 90 % of rotor fault diagnosis, which demonstrates the effectiveness of the proposed framework compared to the model with insufficient fault data.

Time-series signal collected from rotating machinery is subjected to different environmental and operational conditions. The vibration signal is sensitively affected by external noises and load conditions. To solve these problems, this paper presents a diagnostic method for rotating machinery using the proposed robust time-series imaging method. The overall procedure includes the following three key steps: (1) transformation of a one-dimensional current signal to a twodimensional image in time-domain, (2) extracting features using convolutional neural networks, and (3) calculating a health indicator using Mahalanobis distance. Transformation of the time-series signal is based on recurrence plots (RP). The original RP method provides a binary image that makes it insensitive to detecting faulty signal. The proposed RP method develops from sparse dictionary learning that provides the dominant fault feature representations in a robust way. The proposed RP method can detect the weak difference between normal and fault signal, while enhancing robustness to external noise. The dataset acquired from KAIST rotor testbed is used to examine the proposed method’s capability to monitor the condition of rotating machinery. The results show that the proposed method outperforms vibration signalbased condition monitoring methods.

One critical issue of electret-based vibrational energy harvesters (eVEHs) for wearable applications is to improve their adaptability for low-frequency ambient environments. This paper exploits the impact-driven frequency up-converter without coupling phase to improve the power output of an electret-based vibration energy harvester. A vibro-impact model is established, solved numerically by SIMULINK, and verified by SOLIDWORKS/motion study tool. The frequency up-conversion mechanism with delicately avoided coupling phase is demonstrated to improve the power output of the eVEH significantly. According to our analysis, the proposed technique improves the energy harvesting efficiency of eVEH by 40%, for an ultra-low frequency excitation of 2 Hz. By and large, the work of this paper could potentially extend the application of eVEH in low frequency scenarios.

Hard real-time time-series forecasting of temporal signals has applications in the field of structural health monitoring and control. Particularly for structures experiencing high-rate dynamics, examples of such structures include hypersonic vehicles and space infrastructure. This work reports on the development of a coupled softwarehardware algorithm for deterministic and low-latency online time-series forecasting of structural vibrations that is capable of learning over nonstationary events and adjusting its forecasted signal following an event. The proposed algorithm uses an ensemble of multi-layer perceptrons trained offline on experimental and simulated data relevant to the structure. A dynamic attention layer is then used to selectively scale the outputs of the individual models to obtain a unified forecasted signal over the considered prediction horizon. The scalar values of the dynamic attention layer are continuously updated by quantifying the error between the signal’s measured value and its previously predicted value. Deterministic timing of the proposed algorithm is achieved through its deployment on a field programmable gate array. The performance of the proposed algorithm is validated on experimental data taken on a test structure. Results demonstrate that a total system latency of 25.76 µs can be achieved on a Kintex-7 70T FPGA with sufficient accuracy for the considered system.

This study reports the presence of an interface mode in the one-dimensional topologically arranged mechanical metamaterials using mechanical dome shaped metastructures which can be exhibited by hourglass configurations. The paper proposes the method of obtaining a localized interface mode within the bandgap using the hourglass shaped resonating elements in the one dimensional topologically arranged chain. Implementing a wide range of different re-entrant angles on the patterns imprinted on dome shaped hourglass metastructure ranging from negative to positive re-entrant angle would lead to lattice dependent stiffness characteristics in the system. The primary unit cell considered in this system is diatomic unit cell having identical masses and alternating spring stiffness driven by the dome shaped hourglass metastructure. Moreover, the variation in the stiffness of hourglass metastructure is also dependent on the height to thickness ratio which is also explored in this study to restrict the stiffness of hourglass unit in the linear regime which is easily obtainable in small deformation range. The interface unit cell is placed in the one-dimensional chain in such a way that inversion symmetry is broken using the different classes of hourglass lattice metastructures within the unit cell. The frequency response function of the one dimensional topologically protected chain is analytically computed and the interface mode is observed locally within the bandgap. The possibility of wave propagation at specific frequencies within the bandgaps is strategically achieved by defining lattice-dependent stiffness parameters at the interface modes. The considered configurations define a framework for introducing lattice-based imperfections in the continuous elastic structures that makes it potential engineering relevance.

In this work, attention is paid to a SMA blade twist demonstrator conceived for wind tunnel and whirl tower tests, planned in SABRE (“Shape Adaptive Blades for Rotorcraft Efficiency”, an H2020 Project). The model reproduces a blade segment of the Bo 105 helicopter, and aims at demonstrating the effectiveness of an SMA-based architecture (distributed active torsion tube) in altering the original twist to achieve better aerodynamic performance. The full-size device is representative of the original blade segment both geometrically and mechanically, exhibiting comparable performance in terms of mass distribution, and bending and torsional stiffness. Because the maximum allowable length of the SMA actuators undergoing tests was necessarily limited, the abovementioned demonstrator was given a modular architecture and split into different cells (or bays), each containing a single SMA rod. The single cell layout was composed of two main components: a primary structure made of a transversal (main) spar and ribs (the skeleton), and a secondary one made of the skin and its assembly parts. Each SMA rod, activated through a heating coil, is integrated within a box-shaped metallic spar that participates in absorbing loads (passive function) and transmitting twist (active function). The bays are then connected each other by merging the edge ribs; therefore, any complete rib will be made of two portions but the first and last ones. In the paper, a FE model is presented, aimed at verifying the resistance criteria required for the wind tunnel test.