This PDF file contains the front matter associated with SPIE Proceedings Volume 10967 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

Piezoelectric thin films are of increasing interest in low voltage microelectromechanical systems (MEMS) for sensing, actuation, and energy harvesting. The key figures of merit for actuators and energy harvesting will be discussed, with emphasis on how to achieve these on practical substrates. For example, control of the domain structure of the ferroelectric material allows the energy harvesting figure of merit for the piezoelectric layer to be increased by factors of 4 – 10. To illustrate the functionality of these films, examples of integration into MEMS structures will also be discussed, including adjustable optics for x-ray telescopes, low frequency, and non-resonant piezoelectric energy harvesting devices, and miniaturized ultrasound transducer arrays.

By utilizing adaptive features, smart materials can be built as sensors and actuators. Energy can be harvested from vibration and human motion. Piezoelectric and electromagnetic power generators were used to transform the mechanical energy from vibration and human motion into electrical energy. On the other hand, robotic exoskeletons that can assist people with impaired mobility have been developed. With the developed device, paralyzed individual can regain the ability to stand up and walk. Smart ankle-foot prostheses with compact cam-spring mechanism have also been implemented to help amputees walk with less effort while having more natural gait. Utilizing additive manufacturing into smart materials has led to 4D printing technology for creating structures that can change their shape and function on-demand and over time. Actuator units were designed and fabricated directly by printing fibers of shape memory polymers in flexible structures. They can serve as tubular stents and grippers for biomedical applications. In this talk, related research projects and key results will be presented.

Viscoelastic materials are widely used to control vibrations. However, their mechanical properties are known to be frequency and temperature-dependent. Thus, in a narrow frequency bandwidth, there is an optimal temperature that corresponds to a maximum loss factor and it is tricky to get a high damping level over a wide frequency range. Furthermore, an optimal temperature for a maximum structural damping leads to a low static stiffness because the peak of the loss factor is obtained during the glass transition when the storage modulus is decreasing. In order to obtain a compromise between stiffness and damping it is suggested to use a viscoelastic material which properties are functionally graded thanks to a non-uniform temperature field over the structure. In this work, a composite structure has been designed integrating a viscoelastic core and a heat control device. The optimal temperature field has been obtained through the minimization of a cost function that reflects the compromise between structural damping over a wide frequency band and high static rigidity. The experimental validation has been performed on a reduced scale airplane model: the composite wings are sandwich structures made of aluminum skins and a viscoelastic core in tBA/PEGDMA with a non-uniform temperature field and skins are in an aluminum and FR-4. A broadband excitation is produced with a shaker and the measurements are performed with a set of accelerometers. Several temperature fields are tested. The frequency response functions show the compromise obtained between static and dynamic behaviors when using the optimal temperature field determined by numerical simulation.

A light weight and low vibration level panel have been achieved by using PDS (Piezoelectric Damping System). Piezoelectric ceramic actuator has small size and light weight performance owing to PZT (lead zirconate titanate) high force output density in volume and weight point of view. In this research, first we focused on ultra-low frequency (below 10Hz) region anti-resonance property of piezo actuator to piezo sensor transfer function. And then a distance between several actuator was adjusted for the purpose of control a frequency that anti-resonance was occurred. The result shows that over 20dB panel center vibration suppression was performed broadband frequency range. A feedback control was used on this system. Especially a utilization of anti-resonance prevented the oscillation of control system, leads to increase feedback gain. This panel with PDS’s vibration level is as same weight as ten times lager additional conventional damping material’s weight compare to PDS itself (actuators, sensors and controller).

In this study, a semi-active magnetorheological (MR) damper for the main landing gear suspension system of the aircraft is proposed. MR damper is designed with two magnetic cores to control the effective damping force and also with annular bypass for fast expanding speed considering the characteristics of the aircraft landing. A controllable yield force of the MR fluid with respect to the input current is analyzed as a first step, and a vertical landing model with MR damper is considered to evaluate aircraft landing efficiency. In this work, a sky-ground controller is designed and applied to MR damper to maximize the landing efficiency of the drop simulation. The damping force of MR damper is controlled by the input current calculated by the proper choice of the sky hook gain and ground hook gain, respectively. It is demonstrated through the comparative work between the passive and proposed semi-active MR damper based landing gear that the landing gear efficiency of the passive damper can be enhanced a lot showing the efficiency above 90%.

Linear Distributed Parameter Systems are governed by partial differential equations. They are linear infinite dimensional systems described by a closed, densely defined linear operator that generates a continuous semigroup of bounded operators on a general Hilbert space of states and are controlled via a finite number of actuators and sensors. Many distributed applications are included in this formulation, such as large flexible aerospace structures, adaptive optics, diffusion reactions, smart electric power grids, and quantum information systems. Using a recently developed normal form for these systems, we have developed the following stability result: an infinite dimensional linear system is Almost Strictly Dissipative (ASD) if and only if its high frequency gain CB is symmetric and positive definite and the open loop system is minimum phase, i.e. its transmission zeros are all exponentially stable. In this paper, we focus on infinite dimensional linear systems that are non-minimum phase because a finite number of transmission zeros are unstable. Several methods to compensate for this issue modify the output of the infinite dimensional plant and then control this modified output rather than the original control output. Here we use a finite dimensional residual mode filter to modify the output to produce a fully minimum phase system. Then direct adaptive control for the infinite dimensional plant can use this modified output rather than the original output, to achieve ASD and produce asymptotically stability of the states on the Hilbert space. These results are illustrated by application to direct adaptive control of general linear systems on a Hilbert space that are described by operators with compact resolvent.

We present a modeling framework for thin piezoelectric bimorph plates with segmented electrodes acting as electromechanical metastructures (i.e. finite metamaterial structures). Using Hamilton’s extended principle and the assumptions of classical plate theory, the governing equations and boundary conditions for the fully coupled electromechanical system are obtained. The surfaces of the piezoelectric material are segmented into opposing pairs of electrodes of arbitrary shape, and each pair of electrodes is shunted to an external circuit. Using modal analysis, we show that for a sufficient number of electrodes distributed across the surface of the plate, the effective dynamic stiffness of the plate is determined by the shunt circuit admittance applied to each pair of electrodes and the system-level electromechanical coupling. This enables the creation of locally resonant bandgaps and broadband damping, among other effects, as discussed in our previous work. Numerical validations are performed using commercially available finite element software (COMSOL Multiphysics).

This paper proposes a metamaterial beam with local resonators coupled by negative stiffness springs. First, a distributed parameter metamaterial beam model with the proposed configuration of coupled local resonators is developed. Due to the introduction of the negative stiffness springs, the system is prone to be unstable. The stability analysis indicates that the infinitely long metamaterial beam becomes unstable as long as the stiffness of the coupling spring becomes negative. For the finitely long metamaterial beam, the stability could be achieved for given negative coupling springs. A parametric study is then conducted to investigate the effects of the number of cells and the lattice constant on the system stability. The transmittance of the finitely long metamaterial beam is calculated. The result shows that due to the restriction on the tunability of the negative stiffness for the proposed metamaterial beam, a certain trade-off is needed for the appearance of the quasi-static vibration suppression region and the enhancement of the main vibration suppression region.

In this study, an energy harvesting strategy that utilizes the input-independent, invariant transition waves in periodic lattices of bistable elements is explored. We observe that oscillatory tails are induced in a discrete array as transition waves propagate along the lattice. The generated tail at each unit cell vibrates predominantly at a single frequency, which indicates that the tail energy can be efficiently harvested through resonant transduction mechanisms. We introduce inertially and elastically equivalent lattice models to study the discreteness effect of the bistable lattice on the characteristic behaviors of the oscillatory tails and observe that the energy harvesting potential from transition waves can be significantly increased with growing discreteness.

This work documents both modeling and experimental studies of rotary magnetic plucking dynamics in a piezoelectric energy harvester connected to an SECE (synchronized electric charge extraction) interface circuit. The device consists of a piezoelectric cantilever beam fixed on a stationary base and attached to an SECE circuit. A tip magnet is excited by a driving magnet on a rotating host. Energy is therefore harvested by vibration of the beam induced by non-contact magnetic plucking and is enhanced by the SECE circuit technique. In addition, the analytic estimate of harvested power is derived and shows that the device exhibits the phenomenon of frequency up-conversion. The crests and troughs of ripples in the rotatory power frequency response are predicted and are found in good agreement with experiment. Finally, the harvested peak power based on the SECE interface circuit is observed to be twice higher than that based on the conventional standard interface circuit.

Bistable vibration energy harvesters have been used to achieve strong energy harvesting performance over a wide frequency bandwidth. Performance of bistable energy harvesters is dependent on whether the external excitation is large enough to surpass the minimum threshold to high energy, or ‘snap through’ oscillations. Studies have indicated that lowering the potential energy barrier via an auxiliary unit is an effective way to ensure that high energy orbits are achieved. Recent advancements have shown that directly extracting energy from an auxiliary unit used to dynamically lower the potential barrier of a bistable energy harvester can enhance performance. However, there remains an unexplored opportunity for further improvement by incorporating nonlinearity into the auxiliary harvesting element. Thus, to advance the state of the art, this research introduces an energy harvesting system composed of a bistable cantilever harvester magnetically coupled to an auxiliary nonlinear harvesting element. An analysis of the system potential energy indicates that the additional nonlinear characteristics of the coupled harvesting element can enable tailoring of the potential energy profile such that quad-stability, or multi-directional bistability, can be achieved. Investigation of the quasi-static potential energy trajectory of the proposed device indicates that the number of stable states, height of the potential energy barrier, and snap through amplitude may all be tailored through consideration of the effective linear stiffness of the nonlinear harvesting unit. Numerical simulations of the system dynamics indicate that the additional nonlinearity incorporated into the coupled system improves broadband harvesting performance.

Snap-through dynamics between the two potential wells of bistable oscillators are exhibited over a wide frequency range which narrows with decreasing harmonic excitation amplitudes until disappearing at a critical forcing level. However, for efficient conversion from vibrational to electrical energy in harvesting applications, the bistable oscillator must retain its favorable broadband cross-well response while the input excitation is minimized. To maintain effectiveness at low forcing levels, an actuation approach is proposed where external perturbations are used to extend the oscillator’s cross-well bandwidths by switching from co-existing low to high energy attractors. By utilizing Macro Fiber Composites (MFC) in a [0^MFC /90^MFC ]_T bistable laminate, the application of rectangular voltage pulse signals are cycled through different response phases to continuously alter the basins of attraction until the desired cross-well orbit is sustained at each frequency. The pulse magnitude is where the system exhibits limit point behavior and the resulting snap through actuation mechanism brings consistency between perturbation trials. Numerical simulations show significant increase to the bandwidths inducing cross-well oscillations when the perturbation strategy is employed.

Macro-fiber composite (MFC) piezoelectric materials have been applied to a number of problems requiring high actuation authority, ranging from morphing-wing aircraft to vibration control in flexible structures. Most recently we have employed such MFC structures in underwater bio-inspired locomotion employing large actuation levels. However, utilizing the converse piezoelectric effect to such a degree requires high electric field and strain levels, resulting in significant material and geometric nonlinearities, beyond low field nonlinearities typically encountered in energy harvesting and sensing. In this work, we explore the mathematical framework of an MFC bimorph cantilever under low to moderate excitation levels and compare the results to base excitation and actuation experiments. Further experiments are conducted for actuation experiments which result in high strain and electric field levels, and sources of higher order nonlinearities are proposed.

Piezoelectric transducers can convert the mechanical energy into electrical one with their direct piezoelectric effect, or reciprocally convert the electrical energy into mechanical one with their inverse piezoelectric effect. Various applications were developed based on either of these two effects, for example, sensors and energy harvesters using the direct piezoelectric effect and actuators using the inverse piezoelectric effect. Yet, few of them have fulfilled the multi-functional purposes, which are useful in some application scenarios. This paper proposes a bidirectional energy conversion circuit (BECC) solution for the time-division energy harvesting and actuating purposes. The circuit topology is derived from the synchronized triple bias-flip circuit, which was formerly used for energy harvesting enhancement. The circuit topology and control logic for energy harvesting and actuating modes are discussed in details. Two designs are studied for investigating the potential applications of the BECC. In the linear piezoelectric structure, the BECC can be used to provide vibration excitation and then reclaim the vibration energy. Such time-division energy injection and reclamation can be used in some non-destructive structural health evaluations. The proposed BECC can be also used to realize the controllable orbit exciter in nonlinear piezoelectric energy harvesting systems. It is the first time to realize a compact and integrated orbit exciter and energy harvester by using a single interface circuit. Simulations and experiments are carried out for validating the performance of the BECC towards versatile engineering designs.

This work investigates the interaction between a nonlinear slender clamped-clamped beam and a freely movable mass during the passive self-tuning process. The experimental and numerical results illustrate that the hardening nonlinearity caused by the beam stretch strain can broaden the frequency bandwidth. When the amplitude and curvature of the beam at the slider location are large enough, the slider could be driven to move from the side towards the centre and stop around the centre. The slider’s movement, in turn, changes the beam-slider structure’s mass distribution that shifts the frequency response functions to the lower frequency range. During this interaction between the beam and slider, the high energy orbit could be captured with amplified vibration response. Because the slider is driven by the beam vibration, the self-tuning process does not require external energy. Such a beam-slider structure could be used for the design of nonlinear energy harvesting system with the capability of passive self-tuning to acquire large amplitude vibration and thus higher efficiency.

The objective of the manuscript is to explore the effects of geometry on the dynamics of an internally resonant vibrational energy harvester (VEH). Recently, the authors of this manuscript unveiled the existence of ∞^6N solutions to design multi-members resonators which exhibit N commensurate frequencies equal to the number of members of the structure. The generalized topology of this family of resonators which exhibit 1:2 resonance resembles a V -shaped structure, i.e., a structure with two members adjoined at an angle φ, denoted as the folding angle. The classic 1:2 internally resonant L-shaped structure is a subset of solutions in this family. This work investigates the effect of the folding angle on the dynamic response of these oscillators. The nonlinear equations of motion are derived by means of Lagrange’s equation, the beams are inextensible yielding second order nonlinearities. Approximate solutions of the model are obtained using the method of multiple scales. The effect of the folding angle on the nonlinear modal interaction in the power- frequency response curves is investigated.

Energy harvesters with wide frequency range, long lifetime, and high output power are preferred to serve as power supplies for wireless devices. Motivated to guide the design of a robust energy harvesting platform, an analytical model based on the Euler-Bernoulli beam theory for a laminated beam is first presented to predict the nonlinear response of the system when subjected to harmonic base acceleration and tunable magnetic forces. Following experimental validation, a multi-objective optimization based on a genetic algorithm considers how to improve the frequency range of high performance, decrease peak strain level, and maximize output power by manipulating the design of the nonlinear energy harvester. The optimization results indicate that a slightly monostable configuration is superior when taking all three aspects into consideration.

This paper presents the modeling and analysis of a nonlinear wideband vibration energy harvester (VEH) with an asymmetric restoring force. It is commonly recognized that a VEH based on a nonlinear resonator having an odd-symmetric hardening (or softening) restoring force can show wideband frequency characteristics due to its bent resonance peak while keeping its maximum power performance. In practice, however, it often happens that the restoring force has some asymmetry, for instance, due to a bias force (e.g. gravity), or irregular asymmetry in the geometry. In this paper, a hardening resonator with a constant bias force is particularly focused on, and its approximate steady-state solution is studied based on a newly proposed averaging method combined with harmonic balancing. The validity of the approximate solutions are verified by comparing them with numerical solutions. As a result of the approximate and numerical analyses, it is shown that the frequency response displays a resonance peak climbing along an S-shaped backbone curve which is because of the softening effect due to the quadratic nonlinearity stemming from the asymmetry, followed by the hardening nature of the restoring force. Consequently, the frequency response yields the coexistence of multiple stable steady-state solutions on both sides of the resonance peak, and the highest-energy orbit exhibits a well-defined wideband behavior.

Turbulence-induced vibration, particularly one generated by a fractal grid, has not been studied in much detail in the literature. This study focuses on the interaction of two side-by-side piezoelectric energy harvesters in fractal grid-generated turbulence. Three fractal grid patterns have been considered: “I”, square and cross. For each grid pattern, a full-factorial study of four important parameters has been considered: (i) Beam lengths and configurations, (ii) Mean flow velocity, (iii) Distance of the beams from the grids and (iv) the separation between the two beams. Experimental results show that all three fractal grids allowed for a significantly larger power output from the piezoelectric beams compared to a passive rectangular grid with a similar blockage ratio that was previously studied.

The transformation of wind energy into low-power electricity using piezoelectric materials enables the possibility of powering wireless electronic components especially in high wind areas. This work thoroughly explores the effect of aspect ratio (length/width) on the performance of inverted flag-based piezoelectric energy harvesters. Wind tunnel experiments are conducted for a range of electrical loads to quantify the optimal power output. Conclusions are drawn regarding the overall dynamics of the multiphysics system for the design and optimization of this new class of scalable wind energy harvesters.

This paper considers aerodynamic interactions among an array of tensioned ribbon energy harvesters capable of harvesting both wind and solar energy. Each harvester consists of a thin-film solar cell ribbon supported in tension by a pair of piezoelectric bimorph beams in an inverted-U configuration. These ribbons experience aeroelastic flutter when subjected to crossflow, and the energy from these vibrations can be harvested through the piezoelectric beams. The effect of wind speed on the interaction between two fluttering inverted U-shaped aeroelastic energy harvesters configured in a tandem array was investigated, as previous work suggests that synergistic wake interactions can occur between multiple fluttering energy harvesters. An experimental apparatus was constructed and two thin-film solar ribbons were placed in tandem at a fixed separation distance. Each ribbon was given an applied pre-tension, and wind tunnel testing was performed for a range of wind speeds between 7.5 m/s and 12.5 m/s for each ribbon when fluttering in isolation and when fluttering in tandem. Tandem array efficiency was calculated from the experimental data, and it was determined that there is a wind speed at which peak tandem array efficiency (significantly greater than unity) occurs. It was found that this peak corresponds to the wind speed at which constructive interference due to frequency lock between the two fluttering ribbons begins. Results also show tandem efficiency benefits in both the downstream and upstream harvester, as opposed to previous results that show benefits primarily in the downstream harvester. It is hypothesized that these upstream benefits are due to possible base excitations in the apparatus that have been transmitted by the downstream harvester.

Piezoelectric transduction has lately been employed in wireless acoustic power transfer (APT) for powering electronic components that cannot be accessed easily, such as deep-implanted medical devices. Typically, the axial (or thickness) vibration mode of piezoelectric materials is used to generate acoustic waves that propagate through a medium, which are then converted back into electricity and delivered to an electrical load at the receiver end. The piezoelectric receiver can have various aspect ratios (length/diameter) in a given APT application. This work aims to develop and compare various models, such as the classical theory, Rayleigh’s theory, and Bishop’s theory, as well as finite-element model simulations, for different aspect ratios with an emphasis on those with comparable dimensions. Following analytical modeling and numerical simulation efforts, both in air and fluid loaded impedance frequency response functions are compared to report the valid aspect ratio ranges of the respective theories and their limitations, along with comparisons against experiments.

Wind-turbine blades always undergo several surface contaminations such as erosion or roughness variation during operation. Since these cause an early flow separation on the wind-turbine blades, the performance of the wind-turbine also decrease. The level of the surface roughness of blades continuously varies due to the seasonal environmental changes and the contamination accumulation; flow condition on the wind-turbine blades also continuously changes. The flow control devices, therefore, should be able to properly respond to the changes in flow condition. In this study, we evaluated a new type of the vortex generator called a variable-incidence-angle vortex generator (VIVG), which can adjust an incidence angle thereby appropriately responding to the changes in the flow condition. In order to confirm the flow control performance of the developed VIVG, we also designed an experimental airfoil model; the airfoil cross section is DU97-W-300, which was used in NREL 5MW wind-turbine blades. The sandpaper with a grit level of P80 (non-dimensional surface roughness level k/c = 5.03×10^-4) was chosen to emulate the surface contamination of the windturbine blade. We investigated the effect of the incidence angles of the VIVG for surface contaminations through the wind-tunnel test. The VIVG could provide the most appropriate incidence angle with respect to the level of the surface contamination and the angles of attack of the model. These clearly show that the developed VIVG in this study can provide effective ways to overcome surface contaminations in operation.

This paper introduces a hybrid wave-current energy converter (HWCEC) that simultaneously harvests energy from current and waves. Wave energy is extracted through relative heaving motion between a floating buoy and a fully submerged second body. Current energy is extracted using a hydro turbine. A mechanical motion rectifier (MMR) based on one-way clutches merges the separate current and wave power inputs and converts bidirectional, up-and-down wave input motion into unidirectional rotation of the generator shaft through different engagement statuses of the set of one-way clutches. A time domain simulation is conducted with hydrodynamic coefficients obtained from computational fluid dynamics software and boundary element software. Simulation results show an improvement in output energy and peak to average ratio compared to both turbine and point absorber wave energy converters acting individually.

An existing morphing wing design, known as the Spanwise Morphing Trailing Edge (SMTE) actuated by bending the integrated Macro Fiber Composites (MFCs), is considered to generate spanwise positive and negative absolute valued sinusoidal variations along the trailing edge of the morphing wing. Note that this research is an extension of previous studies on SMTE morphing wing design where the deformation of the trailing edge is parameterized as a function of spanwise location using a simple sinusoidal relationship. A comparative aerodynamic study of the morphing geometries by varying the spatial frequency (i.e., number of waves along the span) and the phase shift (i.e., wave shape along the span) at the pre-stall condition is conducted through numerical computational fluid dynamic (CFD) simulations. The results show that high spatial frequencies generate vortices along the wingspan, which significantly increases the drag of the wing. These results further show that the SMTE morphing geometries of high aerodynamics performance lie in the region of low spatial frequency independent of the angle of attack.

This work investigates the development and characterization of a bio-inspired swimmer actuated by Macro-Fiber Composite (MFC) piezoelectric laminates along with the required electronic hardware for untethered underwater operation. The main body of the swimmer is designed to imitate a trout-like streamlined geometry that has a 3Dprinted hard front enclosure and a soft tail portion. The focus is placed on the experimental characterization of the swimmer under various flow conditions and for various actuation frequencies. Straight swimming is explored in quiescent water, and further characterizations are performed in a water tunnel for different flow speeds.

The adoption of mechanical systems represents a very promising solution to realistically enable wing-camber morphing for large civil aircraft. These systems implement the change of shape through the relative motion of parts usually interconnected by means of hinges, and therefore, without any morphing-induced elastic deformation of the load carrying structure; conversely to what happens in compliant structures, the energy provided by the actuation system is here spent to counteract only the external aerodynamic loads which are in turn dependant on shape, speed and flight altitude. Apart of the more effective use of the available power, the mechanical systems show a higher level of technological maturity and readiness for flight thanks to their higher robustness, reliability and maintainability, as well as in force of their similarity with conventional airworthy architectures already in flight. On the other hand, the use of multiple-hinges connections imposes a careful analysis of the effects induced by any degradation of their mechanical performance leading to overall system malfunction or local failures. In the framework of the CleanSky2, a research program in aeronautics among the largest ever founded by the European Union, the authors focused on the design and validation of a camber-morphing flap specifically tailored for EASA CS-25 category aircraft. The shape transition is obtained through a smart architecture based on segmented (finger-like) ribs with embedded electromechanical actuators. Three large tabs were located at the flap trailing edge to actively control the shape of the wing in cruise and to optimize the aerodynamic load distribution along the span. Aeroelastic phenomena related to these flap components were duly addressed since the very preliminary design stage in order to avoid the maturation of a potentially unstable architecture; rational approaches compliant with applicable airworthiness requirements were implemented to properly model and investigate the aeroelastic behaviour of the flap tabs in nominal working conditions. Finally, free plays and internal failures were accurately simulated and their effects on the aeroelastic stability of the aircraft were duly investigated in order to assess the robustness of the conceived tabs as well as of the embedded mechanical subsystems driving their motion.

While the majority of the literature in energy harvesting is dedicated to resonant harvesters, non-resonant harvesters, especially those that use turbulence-induced vibration to generate energy, have not been studied in as much detail primarily due to their comparatively small power output, general non-tunability and difficulty in associating flow conditions to harvester behavior. In this extensive study, we look at the behavior of piezoelectric cantilever beams in different types of grid turbulence with the intention of identifying trends in the harvester output. Our results show that the power-law decay of the harvester output that had previously been observed for rectangular grids holds for a wide variety of fractal grids as well. Additionally, experimental data shows that the average harvester output in grid turbulence follows a power-law growth with respect to the mean flow velocity for relative short and stiff piezoelectric beams.

After pioneering examples in the ’70 and the ’80, technology advances have brought aircraft morphing systems close to the exploitation on commercial vehicles. However, in spite of many successes, further steps shall be accomplished before series production lines are entered. They introduce new needs and sometimes exasperate aspects till now under control in the design phase. The increased number and kind of parts pushes for implementing additive manufacturing techniques; their modelling gives rise in turn to important simulation challenges. In case of mechanical, alternative to compliant systems, modelling of elements shall take in consideration behavior that is substantially different from the analogous counterparts on classical devices. Hinges and torsion bars are more diffused and smaller in these architectures. This work deals with hinges modelling inside mechanically-driven architectures for adaptive winglets. Impact of these aerodynamic surfaces on aircraft stability is crucial and accurate models are required to guarantee their correct implementation. Morphing capability emphasizes this occurrence even more. Schematization effects are investigated in terms of both static and dynamic response. The variation of the deformed shape is therefore examined, identifying the strain map and internal forces distribution changes, essential for design purposes and stress analysis. Modal characteristics deviations are then explored, which may substantially influence aeroelastic stability margins. It is envisaged that this approach could be exploited to consider lags effect. A parametric investigation is finally carried out to identify structural behavior sensitivity to such kind of modifications.

Natural disasters, such as hurricanes, cyclones, and other high-speed windstorm events, pose a threat to the built environment. The damage of the nonstructural components due to high winds, flooding, hurricane surge and rainwater intrusion surrounding a building structure such as the fa¸cade accounts for the majority of the financial loss. The increased interest in the sustainable design of buildings gives forward to the development of creative low energy alternatives for the adaptive fa¸cade. This paper studies five fa¸cade configurations subjected to wind loading. An adaptive diagrid fa¸cade (ADF) is modeled using a panel system of four equilateral triangles: one panel is actuated at the nodes using linear actuators and controls the other three panels in the system. The proposed ADF can be adapted to fit various building heights and shapes and can be chosen due to their structural efficiency that results in material savings and flexibility in designing of complex buildings. This paper makes advances towards an adaptive origami-inspired diagrid fa¸cade has the potential to redistribute wind loads in real-time. With sustainable design becoming an important factor in design, low energy options for the adaptive fa¸cades were considered. This research performs computational fluid dynamic analysis of five threedimensional building structures: a conventional regular building structure, a diagrid building structure without corner columns, and three origami-inspired fa¸cade configurations on diagrid building structures. The purpose of this study is to understand effects of the different building envelope geometries on the fluid dynamics and explore the potential use in optimal shape configuration for real-time morphing adaptation of high-rise buildings subjected to extreme wind loading.

The traditional base-isolated system is vulnerable to long-period ground motions, which usually result in a large displacement concentration at the isolated floor due to the resonant effect. To address this issue, two types of base isolation systems with tuned inerter dampers (TID) composed of a spring, an inerter and a dashpot in serial or parallel, are proposed and evaluated in this paper. The design parameters of the two TID isolation systems are optimized using the H2 norm criteria to achieve the best RMS vibration performance under stochastic excitation. The TID frequency ratio and damping ratio are defined as the design parameters, whose optimal values are analytically derived for the undamped primary system and numerically verified. The results show that the optimum exists for isolation system with serial TID (inerter and dashpot in serious), while in the parallel TID isolation system large TID stiffness and large TID damping are preferred in practice. The parallel TID system cannot be tuned optimally for practical structures, nevertheless, it still achieves a better isolation performance than the optimal serial system by an appropriate selection of the design parameters. The influence of the structural parameters on the optimal design parameters are studied. Case studies are conducted in comparison with the traditional isolation system for a laboratory prototype of a five-story building. The proposed optimal serial TID isolation system has 59% more reduction in the RMS relative displacement between the superstructure and base and 58% in the RMS response of the base vibration under the far-fault earthquake. And 52% and 56% more reductions in the RMS relative displacement and the base vibration are respectively achieved under the near-fault earthquake. The potential power in the TID isolations in earthquakes are also examined.

A control algorithm for shock mitigation system based on magnetorheological energy absorber (MREA) under dropinduced excitation is experimentally investigated, with the objective of “soft landing” (i.e., the final velocity of the payload exactly reduces to zero when consuming the total piston stroke of the MREA). The dynamic model of the shock mitigation system is established. A feedforward damping force tracking approach based on a basic resistor-capacitor (RC) operatorbased hysteresis model is presented and is further employed to accurately describe and predict the hysteretic nonlinearity of the MREA. According to the real-time states of the dropped mass, including the displacement, velocity and acceleration, the system controller outputs the appropriate damping force command to the MREA to achieve the desired minimized deceleration of the payload. The feasibility and the capability of the designed control algorithm are validated via simulation analyses and experimental tests.

The article investigates various cantilever configurations for energy harvesting from rotational motion. A piezoelectric cantilever beam is mounted radially on a rotating body with different configurations. A harvester of type A (type B) refers to an outward (inward) configuration of beam with the direction of the transverse vibration perpendicular to the rotational axis. On the other hand, a rotary harvester of the type C is an outward beam with the transverse vibration in parallel to the rotational axis. A unified approach based on the Hamiltonian principle is employed and the methodology for deriving the formulations is based on the distributed parameter method. The result shows that both the type A and type C enjoy the feature of passive self-tuning of resonance. But the type C exhibits better ability in tuning than the type A. In addition, the type B shows significant harvested power at the cost of loss of tuning ability

In human hand, there are numerous energy sources such as finger bending and grasping. In previous studies, most energy harvesters have been attached to joints. Herein, we use another energy source during finger bending motion. Specifically, we focus on the shape change of the finger from bending and propose a ring shaped piezoelectric energy harvester. It consists of an anterior piezoelectric ring and an exterior silicone ring. We utilize a silicone cylinder to mimic the finger shape change situation. We measure and observe electrical responses from the piezoelectric energy harvester for the finger shape change.

Flexoelectricity is a relatively new phenomenon in research. It bases on a change in polarization caused by changing mechanical strain gradients in dielectric materials. Flexoelectricity is present in all dielectric materials. Different other energy conversion principles are used in energy harvesting or sensor applications. The flexoelectric effect of solids is in a very early stage of research and still far away from practical applications at the moment. Achieving electrical signals by flexoelectric conversion requires changes of mechanical strain gradients in dielectric materials. To generate that, not simple but more complex structures are needed. Furthermore, flexoelectricity of solids is not completely understood yet. Additional investigations in this area of research are necessary to prove the usability of this effect. This paper starts with investigations in this field and discusses a first approach for using the flexoelectric effect from an application-based point of view. As dielectric material, Polyethylene-Terephthalate (PET) polymer films were used in a plate capacitor configuration. A complex measurement setup was built to enable the evaluation of polymer films under changing conditions. The main parameter to verify an energy conversion is the change of system capacitance. First results show a small change in capacitance with time and a capacitance difference dependency on the movement frequency of actuation.

One major challenge to the usability of implants in total knee replacement (TKR) surgery is the limited of the postoperative knee joint loading data; therefore, the ability to continuously monitor these loads is an attractive concept. Integrating an energy harvester to scavenge the energy from human motion enables this monitoring. Recently, Triboelectric Generators have gained attention for energy harvesting because of their flexibility and easy fabrication processes. We investigate a triboelectric energy harvester for load sensing of TKR under simulated gait loading. The performance of triboelectric harvester prototypes was measured under simulated gait loading using a VIVO joint motion simulator. During cyclical loading, triboelectric harvesters undergo a contact and separation mechanism, which led to a voltage potential being generated. The power output is related to the amount of compressive load and the frequency. Therefore, the output power can be used to estimate joint loading and can act as a load-sensing implant component. Aiming to include biocompatible materials, we evaluated the performance of titanium as the triboelectric layer and showed the output is higher compared to Aluminum.

Concurrent energy harvesting by simultaneously harvesting wind and base vibration energy has received very little attention until recently. Yet a major problem with a traditional wind energy harvester under concurrent loadings is the dramatically reduced efficiency when the base vibration frequency deviates from the resonance. This paper investigates a novel design to enhance concurrent energy harvesting from concurrent base vibrations and wind flows. A piecewiselinear aeroelastic energy harvester is integrated with a stopper which can also work as a complementary generator. In order to fast and accurately characterize the response of the harvester, exact analytical solutions are derived based on the harmonic balance analysis and method of averaging. The interaction of the two coexisting excitation frequencies as well as the impact effects between the aeroelastic energy harvester and the stopper are fully considered. Closed-form expressions for both mechanical and electrical responses are presented and validated numerically. Results show that a greatly widened bandwidth is achieved with the proposed design where both aeroelastic and base vibratory energy are effectively harnessed. The analytical solutions are essential to fully understand the characteristics of this new kind of broadband concurrent energy harvester, and serve as a guideline for efficient performance evaluation and parameter optimization.

We propose a novel concept of metamaterials, based on a smart, programmable unit cell. This new metamaterial is presently used to devise new nonreciprocal devices in acoustics, illustrated by the design of an acoustic diode, or isolator. A boundary control strategy was previously shown to provide direction-dependent propagation properties in acoustic waveguides. In this paper, the boundary control is reinterpreted as a source term for the inhomogeneous wave equation, in a purely 1D model. Nonreciprocity is then obtained using a distributed source that replaces the non-standard boundary condition where the normal velocity at the boundary is a function of both pressure and its tangential derivative. Numerical simulations are carried out to validate the theoretical model, and the scattering matrix of the device is retrieved to investigate the nonreciprocal nature of the system. Finally, an experimental validation is carried out and transmission measurements are presented. Results show that the proposed smart metamaterials is able to realize an efficient, ultra-broadband, sub-wavelength, acoustic isolator.

Thermoacoustic systems generate high amplitude sound pressure waves from a thermal input, which can then be harvested via piezoelectric transducers. While a promising concept, current thermoacoustic energy harvesters suffer inherent design limitations which result in: (1) low acoustic power output and simple construction or (2) a reasonable output in a significantly large apparatus (i.e. low power density). The challenge is centered around the working gas oscillations being predominantly standing waves which exhibit a pressure-velocity time phasing that is detrimental to the energy output of such harvesters. The goal of this work is to induce temporal phase adjustments in the excited acoustic waves inside a sealed cavity, thus boosting the amount of useful acoustic power which can be effectively scavenged. By employing open and closed-loop feedback control in a thermoacoustic tube with dual sensing and actuating piezoelectric transducers located at two opposing ends, it is shown that the traveling wave portion of the resultant wave dynamics can be significantly increased with a relatively low level of power pumped into the system. As a result, the controlled device outperforms a conventional one of the same size and configuration and approaches the maximum theoretical potential of thermoacoustic energy harvesting.

This paper investigates potential approaches to delocalize the vibration that result from mistuning in certain cyclic structures. To achieve this delocalization, this paper analyzes a cyclic structure with embedded, adaptive stiffness elements. Cyclic structures are ideally built using identical subsection, mistuning refers to the frequent occurrence that subsections contain some deviations from nominal design parameters. These deviations between otherwise identical subsections can generate localized vibrations. This paper examines using the adaptive structure to achieve different stiffness configurations with the goal of: (1) retuning the structure or (2) decreasing the amplitude of vibration of the localized mode(s). Using a new analysis method developed to identify localized modes of vibration on mistuned cyclic structures, this paper considers a low-order model of a turbine engine blisk with attached adaptive elements. Two method are consider to show the possibility of delocalization. The first method changes the stiffness configuration of the system so that all subsections resonate at the identical frequency. The second method uses a minimization procedure developed to identify the stiffness configurations that minimizes the potential for confined modes of vibration. A mistuned system containing two localized modes was used to test out the delocalization capabilities of each method. Both methods were capable of delocalizing this mistuned system, with method one faring better than method two. Results not only show delocalization, but also that mistuned mode shapes can be distorted back to those of the tuned system.

The auxetic meta-material is a special class of macro-structure designed for exhibiting negative Poisson’s ratio. The spatial repetition of the lattice affects the wave propagation and dynamic responses. In this study, a mathematical basis of Bloch analysis for auxetic media have been presented and shaded some important light on the application of the technique. For this design an analysis has been carried out to show how the periodic boundary condition changes with the connectivity, orientation and geometry of unit lattice. The corresponding eigen value problem is developed to obtain the propagation frequency which is the function of mass, stiffness matrix and the wave vector. Mapping of different forms which are associated with the nodal displacements of a unit cell to adjacent cell have been demonstrated and formulated mathematically and observed its effect on the reduced stiffness and mass matrices is studied. Modal analysis has been carried out using Abaqus 6.14 and the transverse nodal displacements obtained from the F.E analysis. The Bloch formulation for revolving-square type auxetic structure has been formulated and validated. Further, we have obtained the changes in auxetic behavior of the structure under different boundary conditions. The periodicity of a given lattice assists in determining the frequency bands within which the propagation of elastic waves is permitted. Further study is proposed for attenuation and transmission band analysis to steer the waves which roots the idea of vibration sink, in which we can damp the mechanical waves effectively at a specific location. The Auxetic meta-materials is envisaged to have a significant role in wave attenuation and wave steering, and can be used effectively for vibration control.

Inerters are a class of vibration absorber which create a resistive force proportional to the relative acceleration across their two terminals. It has been previously shown that it is possible to create an inerter where the size of this force is variable, through use of a bypass channel controlled by a magnetorheological (MR) valve. However, the requirements and restrictions of such a device mean that existing design methodologies are insufficient. For example, as the pressure drop in the rest of the device is dependent on both the geometry of the device and the velocity of the fluid, it is important to design the valve with this in mind, in order to maximise the control range of the entire device, rather than just the valve itself. This work considers the effects of varying the dimensions of a valve and presents a performance metric to be used to allow comparison of different designs. The results are demonstrated as part of a model of a fluid inerter system.

This research focuses on development a speed control system of a rotary load shaft with different loading torque by using a clutch featuring magneto-rheological fluid (MRC). Firstly, a new configuration of a speed control system using MRC is proposed. Modeling of the MRC based speed control system is then derived based on Bingham plastic model of magneto-rheological fluid (MRF). Based on the derived model, an optimal design problem for the system is built and the optimal solution is obtained based on finite element analysis. Performance characteristics of the MRC based speed control system are then experimentally investigated. After that, the MRC based speed control system to control a varying rotary load shaft driven by an AC motor is proposed and a PID controller to control the speed is designed and implemented. Experiments on steady speed control of the rotary load shaft is then obtained and presented with remark discussions.

In this contribution a design for the enhancement of the torque capacity of energy efficient MRF-based coupling elements will be presented. Magnetorheological fluids (MRF) are smart fluids, consisting of fine magnetic particles in an oil based carrier fluid, with the particular characteristics of changing their apparent viscosity significantly under the influence of a magnetic field. This property allows the design of mechanical devices for torque transmission, such as brakes and clutches, with a continuously adjustable torque generation. Applying the MR-fluid movement control viscous induced drag torques can be eliminated. In combination with a smart MRF-based sealing also losses due to the sealing can be significantly reduced above a well-defined rotational speed increasing the energy efficiency considerably. In addition, the serpentine flux guidance offers an attractive design saving space, weight and feeding energy. For a further enhancement of the torque density certain different possibilities arise. Beside a strengthening due to a combined squeeze and shear mode a design based on multiple axial shear gaps was shown before. Here the most appropriate design will be investigated in more detail. Simulations based on a multiphysic-FEA will be performed and a detailed investigation of the torque enhancement compared to a MRF-based coupling elements with a single shear gap and same outer dimensions will evaluate the degree of torque enhancement.

This research focuses on development of 3-DOF haptic master manipulator featuring Magneto-rheological brakes (MRBs) and a mechanism of spherical manipulator. The haptic manipulator is composed of a spherical manipulating mechanism integrated with 3 MR brakes. The first MRB is a rotary disc-type MRB employed at the waist joint to feedback the tangent force in the horizontal plane, the second MRB is also a rotary disc-type MRB employed at the shoulder joint to feedback the tangent force in the elevation plane, and the third MRB is a linear MRB employed at the prismatic joint to feedback the normal force (approach force). Position of the manipulator’s end-effector is measured by two rotary encoders and an LVDT. After the introduction, a configuration and working principle of the 3-DOF haptic spherical manipulator are presented. Mathematical models of the manipulator are then derived. The MRBs are then optimally designed to provide a required force feedback to the operator. A prototype haptic manipulator is then manufactured and its performance characteristics are then experimentally investigated.

When piezoelectric laminates undergo large deformations, exhibiting a nonlinear stress-strain behavior, and the longitudinal vibrations are not neglected, linear models of piezoelectric laminates fail to represent and predict the governing dynamics. These large deformations are pronounced in certain applications such as energy harvesting. In this paper, first, a consistent variational approach is used by considering nonlinear elasticity theory to derive equations of motion for a three-layer piezoelectric laminate where the interactions of layers are modeled by the Rao-Nakra sandwich beam theory. The resulting equations of motion form into an unbounded infinite dimensional bilinear control system with nonlinear boundary conditions. The corresponding state-space formulation is shown to be well-posed in the natural energy space. With a particular choice of nonlinear feedback controllers, based on the nonlinearity of the model, the system dynamics can be stabilized to the equilibrium. Stabilization results are presented through the filtered semi-discrete Finite Difference approximations, and these results are compared to the ones of the linearized model

Traveling wave piezoelectric transformers are a new type of multi-electrodes piezoelectric transformer allowing to obtain a multiphase system of voltages at the output. The behavior of multi-electrodes piezoelectric transformers is well characterized by an admittance matrix (Y) representing all the couplings between electrodes. The Y parameters can be determined by analytical modelling or as presented in this paper by experimental measurements. In this paper we focus on a cylinder-type multi-electrodes piezoelectric transformer on which we measure the Y parameters with a vector network analyzer. By extrapolation of Laplace expression of the admittances, we represent the Y-parameters as equivalent RLC circuits in order to have a complete circuit model available for simulation with classic electrical simulation software. The results of the simulation are compared to experimental results to validate the modelling approach.

In this article two numerical approaches for the shape prediction of a composite wing panel under the combined actuation of a Shape memory alloy (SMA) wire and a Macro fiber composite (MFC) bimorph has been developed. The first approach is a Euler-Bernouilli beam theory based linear finite element iterative scheme and the second approach is a Timoshenko beam theory based nonlinear finite element iterative scheme that takes into account the von Karman strains. The force due to the SMA wire is modeled as a follower force. It is shown that both the techniques developed are capable taking into account this non conservative follower force, while accounting for any additional arbitrary loading. The numerical schemes developed in this paper are validated using the existing techniques while elucidating the lacuna in the existing methods.

Magnetoelectric (ME) materials have presented themselves appealing towards sensing and energy harvesting applications. Comprehensive studies under linear and nonlinear material behavior have been performed on symmetric ME laminates subjected to homogeneous deformations. However, studies on unsymmetric laminates working under bending action are sparse, despite their advantages like low resonant frequencies. A finite element (FE) model is thus developed in this work based on Mindlin plate theory to quantify the ME coupling under an applied magnetic loading in quasi-static and resonant conditions. Due emphasis has been given to the material nonlinearity of the ferromagnetic phase and the resulting ME coupling in bending and axial as well as torsional modes has been studied. The influence of the frequency of applied AC magnetic field, the magnitude of the bias field and their orientation relative to the plate axes and the effect of plate width are explored for free-free and cantilever conditions. The developed model is also validated against data available in literature. The results illustrate that the cantilever configuration offers a two-fold advantage of high ME coupling and low resonant frequency.

In this contribution a study is carried out for a defined variation of a moving mass based on magnetorheological fluids (MRF). Magnetorheological fluids consist out of a carrier fluid (synthetic-oil) with suspended carbonyl iron powder particles and additives. By magnetically induced volume forces the MRF can be controlled, moved, spatially placed and safely attached at moving parts in order to increase the moving mass on the hand. On the other hand it can be removed and placed in a resting position, like at a housing for example. Among other application this can be utilized in order to change the eigenfrequency of oscillating systems. After introducing appropriate concepts a simulation-based development of a demonstrating prototype for the movement of the MRF will be shown, considering certain designs of magnetic circuits consisting out of permanent magnets and electromagnets on the mover and on the stator. The magnetic designs allows the realization and by this the investigation of the before mentioned behaviors. For the determination of the movement of the MRF multiphysical simulations are carried out. In addition, the developed design is realized to investigate the approach experimentally, too.

Shape memory polymers (SMPs) are used in a wide range of applications in the fields of medicine, electronics, space technology and textiles among others. Consequently, an emphasis on finding an efficient means of actuating these polymers, especially for sensitive and remote applications becomes important. Focused Ultrasound (FU) induced thermal actuation of SMPs has proven to be a safe, remote and flexible technique of achieving spatially and temporally controllable shape recovery. Increasing research is being done to model the shape memory behavior since it forms the basic necessity for SMP use in any application. However, it has mostly been numerical in nature. In this study, we develop a comprehensive analytical model to understand the dynamics of the FU induced shape recovery of SMPs with a focus on acoustic, medium, material and geometric nonlinearities. We estimate the acoustically induced thermal energy inside the SMP and incorporate that energy in an analytical model to understand the change in temperature dependent mechanical properties of SMP as a result of FU exposure. Using these properties, governing equations of motion for an Euler- Bernoulli SMP cantilever beam are formulated through Generalized Hamilton’s Principle. An analytical solution to trace the recovery of the beam is obtained using method of multiple scales for weak geometric nonlinearities. The model is experimentally validated and is able to successfully give a closed form expression for the amount of shape recovery achieved as a function of acoustic parameters, thus eliminating the need of analyzing any intermediary acoustic, thermal and elastic behavior.

This paper presents a unified model of piezoelectric vibration energy harvesters through the use of a generalized electrical impedance that represents various energy harvesting interfaces, providing a universal platform for the analysis and discussion of energy harvesters. The unified model is based on the equivalent circuit analysis that utilizes the impedance electromechanical analogy to convert the system into the electrical domain entirely, where the model is formulated and analyzed. Firstly, the common behaviors of energy harvesters under this unified model are discussed, and the concept of power limit is discussed. The power limit represents the maximum possible power that could be harvested by an energy harvester regardless of the type of the circuit interface. The condition to reach this power limit is obtained by applying the impedance matching technique. Secondly, three representative energy harvesting interfaces, i.e., resistive (REH), standard (SEH), and synchronized switch harvesting on inductor (SSHI), are discussed separately, including their corresponding forms of the generalized electrical impedance and associated system behaviors. As an important contribution, a clear explanation of the system behavior is offered through an impedance plot that graphically illustrates the relationship between the system tuning and the harvested power. Thirdly, the effect of the system electrometrical coupling on power behaviors is discussed. As another important contribution, this paper derives and presents the analytical expressions of the critical coupling of the interfaces, which is the minimum coupling required to reach the power limit and also the parameter used to define the coupling state, i.e., weakly, critically, or strongly, of a system. In particular, the analytical expressions for the SEH and SSHI interfaces are presented for the first time in the research community. Lastly, the system behaviors and critical coupling of the three energy harvesting interfaces are compared and discussed. The SSHI interface has the lowest critical coupling, which explains its superior power harvesting capability for weakly coupled systems.

This letter presents a bi-directional electromagnetic energy harvester (EMEH) that consists of a spherical magnet encapsulated in an arc-shaped tube and two sets of coils wrapped around the tube. Two springs are affixed at the two ends of the tube to reduce the impact-induced energy dissipation and recycle the kinetic energy of the magnet. Experimental studies reveal that the arc-shaped EMEH is capable of capturing energy from ultra-low frequency vibrations that come from two orthogonal directions. Moreover, under the swing motion, the magnet is driven by its geopotential energy to move along the inner surface of the tube and then induce the coils to generate electrical power. Experimental measurements with the arc-shaped EMEH attached on human limbs show that the proposed design could perform simultaneous energy extraction from the vibration and swing motion even though they come from different directions, demonstrating the superior adaptability to the diverse excitations that are abundant in our living environment.

The existing equivalent impedance model of electromagnetic energy harvesters (EMEH) has considered only the single-harmonic relations among the current, voltage, velocity, and force in the dynamic electromechanical system. The modeling accuracy is insufficient, given the interference of high-order harmonics, which gets more severe under practical low-Q (quality factor) induction coil designs. This paper introduces an improvement to the conventional single-harmonic model by taking into account the influence of the practical low-Q coil and the high-order harmonics in the EMEH system. The extended impedance method (EIM) is used to characterize the nonlinear components in the system. The improvement of modeling accuracy is validated by experimental results.

Recent researchers have focused on scavenging energy from ambient vibrations or movements by using piezoelectric energy harvesters. Rotary movements are regarded as potential energy resources as they can be utilized in windmills or turnstile gates in stations. This study aims to study the vibrational interference that could occur in the typical rotational plucking energy harvester with circularly distributed plectra on the outer ring plucking on the circular array of multiple piezoelectric cantilevers on the inner hub. In this structure, the plucking frequency will be increased to times of the input rotational frequency since multiple plectra will participate in the deflection of each piezoelectric cantilever for one rotational cycle. A model is established based on the Hamilton’s principle for the basic electromechanical part and the Hertzian contact theory for the solution of plucking force. Based on the developed model, the simulation results of the system responses of the rotational plucking energy harvester (RPEH) in a wide rotational frequency range reveal that the system may be suppressed by the vibrational interference such that the energy output is restricted as the rotational frequency is increased. The induced plucking force has also been plotted to reproduce the dynamic contact process and investigate the variation of the force amplitude with rotational frequency. An overall investigation of the energy harvesting performance also indicates the influence of the vibrational interference on the RPEH structure.

Wind turbines and aircraft structures require smooth surfaces due to the aerodynamic requirement. The surface mounted transducers for structural health monitoring disturbs the airflow over the surface. Embedding the sensors in the structures is a viable solution, which also leads to the self-protection and shielding of the sensors. A brief review of techniques to embed the sensors and their wiring is provided. Materials like piezo-polymers, nanocomposites, macro-fiber composites and ceramics have been investigated for the compatibility with composite laminate. The atomistic-continuum, micromechanics and finite element based approaches used to derive the effective properties of nanocomposites have been discussed. With the capability to change the density and stiffness of nanocomposites, the possibilities of very high compatibility with the host structure are explored. The relation of compatibility with the material parameters like density, axial stiffness, coupling stiffness and flexural stiffness has been discussed. We present the effect of embedding thin film sensors on the dynamic response of a composite laminated beam using a spectral finite element model. The change in stiffness and natural frequencies have been quantified. The study provides a strong base to design embedded sensing technology for advanced structures made of composite laminates and sandwich sections.

This paper proposes a pulse-echo ultrasonic propagation imaging (PE UPI) system for non-destructive evaluation of structures. The system can perform scans of any shape and can autonomously suggest the optimal scan area best suited for a given specimen. The system uses the bulk waves, which travel through the thickness of a specimen, for subsurface feature detection. This is achieved by joining the laser beams for the ultrasonic wave generation and sensing. Since bulk waves are less susceptible to dispersion during short travel time through the thickness, precise and clear damage assessment and defect localization is possible with minimum signal processing. The system uses a Q-switched laser for generating the ultrasonic waves, a laser Doppler vibrometer (LDV) for sensing, optical elements to combine the generating and sensing laser beams, a dual-axis automated translation stage for raster scanning and a digitizer to acquire the measurements. The system also employs a camera in its scan head to aid in customizable and automatic scan boundary delimitation. A graphical user interface (GUI) has been developed in C++ using QT framework. The software is used for autonomous scan area delimitation, signal acquisition, signal processing, result display and post-processing algorithms. The GUI is designed with a minimalist approach to promote usability and adaptability. Through the use of multi-threading, the software is able to show the results in parallel with an ongoing inspection. This is achieved by real-time and concurrent acquisition, processing, and display of ultrasonic signal of the latest scan point in a scan area.

Crack rubbing or clapping in metallic structures generates acoustic emission (AE) signals. Such AE signals need to be distinguished from AE signal due to fatigue crack growth event. AE signal due to crack rubbing or clapping of fatigue generated crack was studied for a plate specimen. 20 mm fatigue crack was generated in a 1 mm thick aluminum plate specimen. Vibration-induced excitation was performed on the specimen to induce crack faying surface-motion for AE signal generation. Various specimen resonances have different crack faying surface motions, which were studied from FEM analysis. Modeshapes and crack faying surface motions of the specimen are studied at 35 Hz and 180 Hz specimen resonances. AE signals at various specimen resonances were recorded by piezoelectric wafer active sensors (PWAS) and the recorded waveforms are analyzed to obtain AE signatures. At various specimen resonances, AE signals have different signatures due to the change in crack faying surface motions. AE recording was done by using multiple PWAS sensors placed at various distances from the crack. The difference in AE signals close to crack and distant from crack as well as the geometric spreading of AE signals originating due to crack rubbing was studied from multi-sensor experiments.

The use of smart sensors has been increased for several applications. The measurement of a surface motion and its strain, typically, is done with strain gauges. However, these transducers are not easy to use nor maintain in right conditions. This work explores the use of smart materials as new transducers for vibration and strain. The conceptualization of a smart sensor using Magneto-Rheologic Elastomers and Piezoelectric transducer is presented. The setup of the prototype as a sensor for the internet of things allows to show and log the results in the cloud. The fabrication of a prototype and its study under a set of experiments shows the resistivity variation due to physical manipulation and the capability of voltage generation under vibration can be used to create a new sensor technology.

Just as it is indubitably accepted that the piezoelectric actuators do not behave in a linear fashion when subjected to strong electric fields, it was also believed that they behaved in a linear manner at weak electric fields excitations. But this notion was shattered by the experimental evidence offered by researchers in recent years, where it was observed that the piezo-actuators behaved non-linearly even when actuated at voltages which resulted in weak electric fields in the piezoelectric actuator. Most of the experiments, however, were conducted on the piezoelectric patches, and consequently most of the studies were aimed at establishing the non-linear relationship in the “31” electromechanical coupling, and the nonlinear elastic relation of the material along the longitudinal axis. Though this may be expected due to the widespread usage of the patches, the “33” coupling needs to be investigated too —as stack actuators are the preferred ones for the actuation of large structures. This study aims at characterizing the nonlinear behavior both in the patches and the stacks; thereby establishing the nonlinear constitutive equations for both the “31” and “33” coupling. To achieve this, a two-step experimental procedure was followed, wherein, firstly, the mechanical domain was isolated and studied to establish the non-linear elastic behavior. Later, equipped with the nonlinear stress-strain relation, experiments were conducted to identify the nature of the nonlinearity in the electromechanical coupling. Unlike the two-step experimental procedure, which facilitates a separate investigation into the mechanical domain and the electromechanical coupling, the experimental procedures employed in the previous studies yield data which mixes the contributions from both the mechanical domain and the electromechanical coupling. The experiments were conducted to obtain a family of displacement frequency response curves of the bending modes of a piezoelectric-beam and a piezostack-beam. The information from the displacement frequency response curves, and the profile of the backbone curves, obtained from both steps of experimentation, were used to determine the exact nonlinear terms required to represent the observed phenomenon. Eventually the nonlinear constitutive equations were constructed with these terms.

In this work, the notion of using surface bondable piezoelectric actuators, which directly use the “33” electromechanical coupling, for actuating large structures is investigated. This concept was a result of the attempt to control the vibrations of a steel marine platform with piezoelectric actuators. Piezoelectric actuators find applications both in the excitations of membrane-like structures, wherein thin patches are bonded to the surface of the substructure to, and in the excitation of large structures, where piezoelectric stack actuators are conventionally employed akin to an electrodynamic exciter with stringer —to provide transverse loading. For the case of the actuation of the marine platform, the use of the piezoelectric stack actuators in a conventional manner could not be suggested for implementation on the actual structure due to its associated drawbacks. As an alternative, the concept of the surface bondable piezoelectric stack actuators was proposed. This design allows the stack actuators to be bonded to the surface of the structure (like a patch), and just like the patches, on the application of an external electric field would generate axial forces on the surface of the structure. In this study, the design of such an actuator is elaborated; following which, an analytical model is derived for beams with surface-bonded stack actuators. The analytical model is derived for the bending vibrations of the structure, and is used to investigate the necessity of the design and the actuation capability of the surface-bondable stacks. The actuation capability of the surface bondable stacks are compared with the actuation capability of other stack implementations, and with similar sized piezoelectric patches. Finally, experimental evidence is provided to demonstrate the practicality of the design.

Through an impedance plot obtained from the equivalent circuit modeling of linear energy harvesters, this paper provides explanations of their system behaviors such as power and efficiency. The impedance plot shows the tuning impedance and the matched source impedance in the same graph, providing a visualization of their relationship as the system parameters are changed or tuned. Using this relationship, the power characteristics of the system are clearly explained. In addition, the impedance plot is connected to the structural effects in stiffness and damping due to energy harvesting. Two types of efficiency are defined in terms of the electrically induced damping: the energy conversion efficiency and conventional energy efficiency. By using the impedance plot, it is shown that the maximum power and maximum efficiency are achieved almost simultaneously for weakly coupled systems. However, for strongly coupled systems, they cannot be achieved at the same time due to the significant reduction in structural energy associated with high efficiency. Though many relationships discussed in this paper are reasonably understood in the research community, a deeper and more direct understanding of these relationships are offered by this paper with the aid of this graphical and intuitive approach.

Dynamics of periodic structures has fascinated researchers for decades. Metamaterials are one of the exemplars of these periodic structures. Spatial periodicity of mechanical unit cells in artificially engineered metamaterials exhibits idiosyncratic physical properties like negative mass, negative Young’s modulus, and negative Poisson’s ratio. These extreme physical properties are beyond the properties found in the natural materials. This exceptional dynamic behaviour is frequency dependent, which in turn forms the attenuation and transmission band during wave transmission through these metamaterials. The frequency ranges in which a wave can transmit or attenuate along the length of the metamaterial are known as transmission and attenuation bands respectively. In this work, the band structure of piezo-embedded negative mass metamaterial is analysed using generalized Bloch theorem. The addition of the piezoelectric material at the resonating unit increases the damping and complexity of the solution. Bloch theorem is used to solve several periodic media and using this theory, the relationship between frequency and wavenumber can be established. Implementation of Bloch theorem has not been reported yet in the context of the piezo embedded mass-in-mass metamaterial. Therefore, wave propagation through finite units is studied through band structure. In addition, voltage and power produced by piezoelectric material are estimated. This research can be considered as the first step towards modelling an active metamaterial.

The cantilever beam type of PEH (piezoelectric energy harvester) has been widely studied for years due to simple design and effectively generate high strain and high ouput power. In our previously researches, the PEH unit with area of 6 mm by 9 mm has output performance around 300 μW under base excitation of 0.5g acceleration level. Moreover, we have designed the tapered shape cantilever beam of PEH for optimizing the beam strain distribution and verified that the output performance and durability are not inferior to rectangular one we have fabricated before. In this study, the tapered shape cantilever beam PEHs are chosen for durability experiment to investigate the relevance among output performance, fatigability and mechanical properties of devices with a long-term working period under different working temperature. The result evidently shows the durability difference when the device is operated under high temperature (50°C) with significant natural frequency drop and the PEH could not maintain constant power output.

This article presents the recent study in guiding acoustic waves by creating frequency band gaps and harvesting energy simultaneously from the vibration of the structure using split ring metamaterial. Traditionally, conventional materials are unable to create frequency stop bands. So, split ring metamaterial has been used which has shown the ability to filter acoustic waves in a certain frequency range by creating frequency stop bands. In this article, a 3D unit cell of aluminum with continuous periodicity and certain split ring resonator pattern is discussed. PVDF film is used in the structure as a piezoelectric material. Here, a wide range of frequency (0-30kHz) is studied to demonstrate the ability of the cell to create stop bands within the study range. From the study, it can be seen that this unit cell is capable of creating stop bands and at the same time harvest ~2.4μW of energy simultaneously under 10kΩ resistive load.

The transport and civil industry research has been aiming at improving vibro-acoustic performance of panel-like structures such as trim panels, glazing windows or separating walls. Focusing on the airborne path, the application of an active control for optimizing the plate acoustic isolation performance is here investigated. A transmission model of an acoustically excited plate is derived in the time domain predicting the plate velocity and its acoustic radiation. The dynamic system is modelled together with the control loop in MATLAB where a suitable control algorithm for enhancing the panel transmission loss performance is developed.

This paper presents an effort to achieve a nonlinear wideband vibration energy harvester (VEH) with a self-powered stabilization control which is introduced to resolve the well-known problem of the coexisting solutions in the resonance frequency band. The most significant issue on the wideband VEH using a nonlinear oscillator is the difficulty of coexisting solutions, because of which the emergence of the response in the high-energy branch is not guaranteed since it depends on the initial conditions to which steady-state solutions the state is attracted. Thus, a response stabilization control has been proposed by introducing a negative impedance converter (NIC) which returns the harvested energy to the resonator to destabilize the undesirable lower-energy solutions and make the highest-energy solution globally stable. However, the power necessary to operate the control was supplied by an external power source in the previous studies, so that the power consumption by the control circuit is still a critical problem. In this study, the suppression of the power consumption to drive the operational amplifier in the NIC, the power consumed in the switching circuit, and the power to operate the microprocessor has been discussed. A self-powered control circuit has been designed and developed, and it has been demonstrated that it can perform the response stabilization control in a single manner. Successive operation is still a critical problem which requires further understanding of the mutual constraints among design parameters and operation conditions.

This study shows an active vibration control using a phase and an amplitude of a mean field of oscillators. Recently, we have proposed an active mass damper (AMD) system using a neural oscillator, which can flexibly synchronize with a target structure’s vibration response. In the proposed system, a neural system including a single oscillator and a position controller form the controller: the neural system generates a target path of an auxiliary mass of the AMD and then, the auxiliary mass is position controlled to the target path to absorb the vibration energy of the structure. However, the oscillator could unfortunately include a non-linear response when the frequency of the periodical input is dramatically different from the oscillator’s eigen frequency. To suppress the undesirable single component of the control signal, this study will use the phase and the amplitude information of an arithmetic mean of the oscillators for the target path of the auxiliary mass of the AMD. Cleaning the control signal could improve an input-output stability of the proposed system and enable to vibration control a specific vibration mode of a multi-degree-of-freedom system such as high-rise buildings.

This paper presents a design study of a miniaturized nonlinear vibration energy harvester based on a mechanically and magnetically-sprung resonator for a low-frequency application. The resonator to be investigated consists of a moving magnet composite as a mass, which is sprung by two planar springs and two fixed ring magnets. The planar springs with spiral-like shape are respectively connected to the both ends of the magnet composite so that they can provide a linear stiffness in a compact size. Mechanical stoppers installed to constrain the deformation of the spring give the resonator hardening characteristics which effectively widen the resonance band. The magnet composite is comprised of two repelling cylindrical magnets and a steel disk between them, all encapsulated in a thin stainless steel cylinder whose outer diameter is smaller than the diameter of the ring magnets. The pole arrangement of the ring magnets is repelling so that they can suspend the magnet composite between them. This configuration of the magnets yields a local minimum in the magnetic attractive force between the magnet composite and the single ring magnet. Consequently, it can show either monostable or bistable property depending on the distance between two ring magnets. If the distance is adjusted so that the bistability emerges, it can cancel the linear stiffness of the planar springs, so that the overall bandwidth can be extended lower which is suitable for low frequency application. In this paper, the hardening effect of the proposed mechanical stopper arrangement is examined by an initial prototype of a miniaturized electromagnetic harvester designed and fabricated without ring magnets. The performance of the harvester in terms of the frequency responses demonstrates a pronounced band widening effect due to the proposed stopper arrangement.