Patch Actuators Research Articles

Experimental validation of an hybrid analytical-numerical technique to estimate the directivity of ultrasonic piezoelectric actuators

The generation of guided waves is a common approach for structural health monitoring. The optimization of the excitation strategies very much benefits from the availability of efficient simulation tools. On the one hand, the application of finite elements (FEs) for the analysis of wave propagation problems leads to large models which tend to be computationally costly for optimization studies. On the other hand, semi-analytical approaches provide useful analytical expressions for parametric studies, but may lead to inaccurate estimations of tuning frequencies and directionality, especially at high frequencies. This is mostly because of the simplifying assumptions regarding the stress field at the interface between the actuator patches and the plate. An interesting methodology couples the analytical far-field solution of the plate response with a local FE model of the interface stresses between plate and patches. This method allows the analysis of complex actuation configurations for various purposes, such as directivity steering. In this contribution, we experimentally validate such hybrid FE-analytical technique. A Scanning Laser Doppler velocimeter is employed to retrieve both temporal and spatial Fourier Transforms on a polycarbonate plate, excited by piezoelectric patches, and the directivity patterns of the first symmetric and antisymmetric modes are compared to the numerical predictions.

Application of intelligent controller to speed up vibration attenuation of a sandwich smart structure subjected to external excitation

Intelligent controllers represent a class of advanced control systems designed to adapt, learn, and make decisions based on changing environments and dynamic conditions. These controllers leverage artificial intelligence and computational techniques to enhance traditional control methods, providing a level of adaptability and sophistication that is particularly valuable in complex and uncertain systems. In this work for the first time, the Proportional–integral–derivative (PID) controller the intelligent controller is used to speed up vibration attenuation of a sandwich smart structure subjected to external excitation. The sandwich smart structure is made of a composite core and sensor and actuator patches. Using shear deformation theory, Hamilton’s principle, and compatibility equations, the governing equations of the sandwich smart structure under external excitations are obtained. After that using numerical solver and time-dependent solution procedure, the equations are solved. After obtaining the datasets via mathematical modeling, this kind of dataset is used as the input and output data to train, validate, and test the machine learning method to use it with low computational cost. After that, using this kind of machine learning method, future researchers can use it to estimate a control vibration of the sandwich structure after mechanical excitation. The results suggest some applicable recommendations to speed up the vibration attenuation of a sandwich smart structure subjected to external excitation.

Development of an Asymmetric Hydrophobic/Hydrophilic Ultrathin Graphene Oxide Membrane as Actuator and Conformable Patch for Heart Repair (Adv. Funct. Mater. 32/2023)

Development of an Asymmetric Hydrophobic/Hydrophilic Ultrathin Graphene Oxide Membrane as Actuator and Conformable Patch for Heart Repair (Adv. Funct. Mater. 32/2023)

Development of an Asymmetric Hydrophobic/Hydrophilic Ultrathin Graphene Oxide Membrane as Actuator and Conformable Patch for Heart Repair

AbstractA conductive engineered cardiac patch (ECP) can reconstruct the biomimetic regenerative microenvironment of an infarcted myocardium. Direct ink writing (DIW) and 3D printing can produce an ECP with precisely controlled microarchitectures. However, developing a printed ECP with high conductivity and flexibility for gapless attachment to conform to epicardial geometry remains a challenge. Herein, an asymmetrical DIW hydrophobic/hydrophilic membrane using heat‐processed graphene oxide (GO) ink is developed. The “Masked spin coating” method is also developed that leads to a microscale GO (hydrophilic)/reduced GO (rGO, hydrophobic) physiological sensor, as well as a macroscale moisture‐driven GO/rGO actuator. Depositing mussel‐inspired polydopamine (PDA) coating on the one side of the DIW rGO , the ultrathin (approximately 500 nm) PDA‐rGO (hydrophilic)/rGO (hydrophobic) microlattice (DrGOM) ECP is bestowed with the flexibility and moisture‐responsive actuation that allows gapless attachment to the curved surface of the epicardium. Conformable DrGOM exhibits a promising therapeutic effect on rats' infarcted hearts through conductive microenvironment reconstruction and improved neovascularization.

A flexoelectric actuator model with shear-lag and peel stress effects

Flexoelectric materials are being extensively studied in recent years for potential sensing, actuation, energy harvesting and structural health monitoring applications. However, no analytical model exists in the literature to predict the stress transfer between a flexoelectric transducer and the host structure, considering bonding compliance. In this article, we present an analytical model for the interfacial stresses and deformations of flexoelectric patch actuator(s) bonded to an isotropic host plate considering both shear-lag and peel stress effects at the interface(s). The model is valid for both piezoelectric and flexoelectric effects. The system’s one-dimensional governing equations are derived consistently from the three-dimensional equations for linear dielectric solids obtained using the bulk electric Gibbs energy density function and extended Hamilton’s principle. The transducer and substrate, modelled as classical Kirchhoff plates, undergo both extension and bending deformations. The formulation produces a seventh-order differential equation for the interfacial shear stress, which is solved analytically, satisfying all boundary conditions. The solution is validated by comparing with the available results for piezoelectric actuators with a non-rigid interface and those of flexoelectric actuators based on the pin-force-moment model assuming a rigid interface. Detailed numerical studies are presented to show the effect of the plate, actuator and adhesive parameters on the interfacial stresses and deformations. Finally, the size effect of the actuators at the micro-scale is illustrated.

Excitation of torsional guided waves with flexible PZT transducers in water-filled pipes

Estimation of structural damage to predict the service lifetime of liquid-filled pipelines is important to reduce waste or to avoid accidents. In this work, experimental and numerical simulations were carried out to characterize the acoustic wave propagation of the lowest cylindrical torsional mode in a pipe with discontinuities. Wave mode was generated and received using flexible macro-fiber composite transducers (MFC). An analysis of beam energy directionality of shear horizontal (SH) and Lamb modes was carried out prior to the tests on the cylindrical structure. A method to control the generation and detection of torsional waves in the pipe considering the directionality of the SH-plate waves was proposed. Tests were carried out in a water-filled pipe to study the leakage effect in the detection of discontinuities. The results showed that although torsional as well as flexural modes can be simultaneously excited by the MFC patch actuator, the orientation of the patch can also allow mode selection. Finally, it was found that flexible patches generate torsional waves efficiently and could be used to detect circumferential discontinuities in water-filled pipes.

Chatter suppression for milling of thin-walled workpieces based on active modal control

Owing to the low stiffness of workpiece, chatter easily occurs in milling of thin-walled structures, which may cause poor surface quality and uncontrolled machining accuracy. For suppressing milling chatter of thin-walled workpieces, this paper presents an active control method with a piezoelectric patch actuator. As a flexible body, thin-walled workpieces have more than one modals participating in milling vibration, and its dynamic characteristics vary with tool position. This paper establishes dynamic model of the thin-walled workpiece with a semi-analytical method. Considering three order modals of workpiece, actuator position is optimized and active controller is designed. The varying dynamic characteristics of workpiece are overcome by designing controller with the parameters on the maximum vibration position to stabilize the whole process. Experiments verify the necessity of considering more than one modals of workpiece in active control through various chatter characteristics dominant by different modals. With the designed control method, the stable cutting depth improves from 0.2 mm to 1 mm.

PZT actuators as on-board instruments to reduce vibrations and strains in submerged structures

This paper presents the design and evaluation of an active control system to reduce vibrations and strains of submerged structures. For that, a metallic disk mounted in a test rig has been equipped with on-board waterproof strain gauges and accelerometers, to measure its structural response, and with an on-board PZT actuator patch, to provide the required control force. This control force is computed in real-time by an optimal algorithm that determines the exact voltage to be supplied to the PZT patch in order to mitigate any increase of vibrations and/or strains detected by the sensors. In order to capture the dynamics of the structure when it is excited both in air and submerged in water, a plant model has been identified from the Frequency Response Functions (FRFs) obtained experimentally from the measured vibrations and numerically from simulated strains. With these plant models, two different control techniques based on a Linear Quadratic Gaussian (LQG) controller and on an H ∞ controller have been implemented and simulated under different types of excitations. The obtained results are satisfactory and support the need to continue the research to validate them experimentally.

Active vibration control of large space structures: Modelling and experimental testing of offset piezoelectric stack actuators

To meet demanding mission objectives, most current satellites for Earth and Universe observation are equipped with large flexible appendages. However, due to the coupling between spacecraft rigid and elastic dynamics, unwanted elastic vibrations of such flexible elements may compromise the achievement of pointing and stability requirements. Therefore, control solutions aiming at avoiding instabilities and, at worst, the failure of the mission, are currently needed. In this scenario, growing interest has been recently devoted to Active Vibration Control (AVC) strategies relying on the use of smart materials. Among them, piezoelectric patches are the most studied and tested devices for both actuating and sensing purposes. This paper aims to contribute to this line of research by investigating a different type of actuator, namely an Offset Piezoelectric Stack Actuator (OPSA), to assess its performance in damping out elastic vibrations of large space structures. Moreover, special attention is devoted to compare OPSA performance with standard patch actuators behaviour. In order to develop the AVC system, an equivalent electro-mechanical coupled Finite Element (FE) formulation is implemented, integrating both sensors and piezo-stack elements on the passive hosting structure. The final structural model including both electrical inputs/outputs, as well as modified mass and stiffness due to the additional piezo devices, is then obtained. A parametric analysis is carried out to optimize the maximum control action exerted by the OPSA device. Finally, the OPSA numerical model is experimentally validated by mounting it on a cantilever plate, representative of a scaled solar panel. Experimental data are used not only to verify the device expected functioning, but also to tune the parameters in the OPSA FE model, which can be finally integrated in a planar satellite dynamics simulator to evaluate the AVC system efficiency when performing attitude manoeuvres.

Mode-I fracture control of unidirectional laminated composites using MFC actuators

This article presents an experimental and numerical investigation of Mode-I fracture control in aerospace grade unidirectional laminated composites (AS4/914) using the smart material approach. The P1 type macro fiber composites (MFC) actuators are selected for current research because of their higher free strain, high mechanical flexibility, and good blocking force. The opening mode (Mode-I) interlaminar fracture tests have been carried out on DCB specimens having surface bonded MFC actuator patches under the application of electric voltage within a range of 0–1500 V. These fracture control tests have been performed on pre-cracked (PC) and non pre-cracked (NPC) double cantilever beam specimens. The modified pin force model has been adopted for the evaluation of actuation forces in surface bonded MFC actuators. The XIGA-CZM based numerical formulation is utilized for numerical fracture modeling under electromechanical loading conditions. The MFC actuators have significant control over Mode-I fracture energy under the application of peak operating voltage. The numerical model using a modified pin force model in combination with XIGA-CZM based fracture model shows a good agreement with experimental observations.

Nonlinear static analysis of composite beams with piezoelectric actuator patches using the Refined Zigzag Theory

Piezoelectric actuators have been highly successful in a wide range of structural control applications. As such, there is an ongoing need for rapid and accurate structural analysis techniques, particularly for highly heterogeneous composite materials and accounting for the actuator as a patch.Here, a new model based on the Refined Zigzag Theory (RZT) formulation that includes geometric nonlinearities is proposed for buckling, postbuckling and nonlinear static response analyses of geometrically imperfect composite beams with piezoelectric actuators.Both the analytical and the finite element (FE) formulation are presented for symmetrically and non-symmetrically laminated beams. The FE approximation is further generalised to the case of beams with geometric discontinuities to model composite beams with piezoelectric actuator patches. The new RZT model is numerically verified through comparisons to Abaqus solutions for buckling and postbuckling analyses and for the geometrically nonlinear response to an applied voltage of geometrically imperfect composite beams with piezoelectric actuator patches.This work presents a new model for composite beams with piezoelectric actuators and confirms the remarkable advantages of RZT in terms of accuracy and computational efficiency also for challenging nonlinear analyses, where the RZT computational time is generally less than half the time required by the FE commercial code.

Piezo-based flexural vibration suppression for an annular rotor via rotating-frame H2 control optimization

Elastic vibration can arise in annular and thin-walled rotor structures, impacting on operating performance and the risk of failure. Feedback control to reduce flexural vibration can be realized using lightweight actuators and sensors embedded in the rotor structure. To design optimal controllers, rotating-frame models of both the structural dynamics and sources of excitation are required. This paper describes a solution to this problem for the case of an annular rotor equipped with piezo patch actuators and sensors. To account for space-fixed external excitation sources, a forcing function is considered involving specified spatial and frequency domain distributions. A model-based [Formula: see text] synthesis is used to compute optimal control solutions. These are tested experimentally on a thin-walled cylindrical steel rotor for cases with narrowband and broadband excitation sources, applied from the fixed frame. The results show that frequency-splitting within the rotating-frame dynamics plays a key role in predicting and controlling resonance. The effectiveness of the optimal control methodology in reducing circumferential vibration of the annular rotor is also confirmed.

Mini-max optimization of actuator/sensor placement for flexural vibration control of a rotating thin-walled cylinder over a range of speeds

For a rotating thin-walled cylinder subject to flexural vibration, active control can be applied using surface-mounted actuators and sensors. To achieve acceptable vibration control performance, the dependency of the dynamic behaviour on rotational speed must be accounted for in the control system design, including the selection and positioning of actuators and sensors. A key issue is that the natural modes of vibration of the cylinder wall involve circumferential travelling waves and, for certain rotational speeds, the frequency of a backward wave for a low order mode can become equal to that of a forward wave for a high order mode. It is shown that these frequency-crossings have important implications for the actuator/sensor placement problem due to the potential for loss of controllability. Accordingly, an actuator/sensor placement approach is introduced based on a mini-max optimization, where the system controllability is maximized for the worst-case rotational speed within a specified interval. Placement solutions are obtained through the application of a nested particle swarm optimization algorithm, used to find saddle-point solutions. The approach is shown to be effective for cases involving 2, 3 and 4 actuator/sensor pairs and with multi-mode model (including up to 16 modes). The results are confirmed by experiments on a thin-walled rotor system with piezo patch actuators and sensors, where H2 control algorithms are applied to suppress vibrational resonances within a control bandwidth of 200-1200 Hz. The potential for loss of controllability at certain rotational speeds is confirmed, as well as the effectiveness of the optimal placement solutions in maintaining control performance over a targeted range of speeds.

Shear actuation-based hybrid damping treatment of sandwich structures using a graphite particle-filled viscoelastic layer

In this work, the effectiveness of a shear actuation-based hybrid active-passive damping treatment is investigated by incorporating the inclusion of graphite particles within the viscoelastic damping layer. The study is performed through the flexural vibration analysis of a sandwich plate-strip where the core is made of a laminate of active layers and graphite particle-filled viscoelastic layers in two different stacking sequences. The active layers are comprised of shear mode piezoelectric actuator patches that are activated according to a shear-based velocity feedback control strategy. The analysis is performed by deriving a closed-loop finite element model of the sandwich plate-strip, and it reveals that the hybrid damping is significantly dependent on the stacking sequence of active and passive damping layers at the core. The inclusion of graphite particles not only provides augmented passive damping but also causes enhanced transfer of shear actuation force from the active layers to other layers. As a result, a significantly improved shear actuation-based hybrid active-passive damping is achieved due to the inclusion. The effectiveness of this hybrid damping in attenuation of resonant displacement-amplitude is also presented by configuring the volume fraction of graphite particles and shear actuator patches in an optimal manner.

Nonlinear vibration of conical shell with a piezoelectric sensor patch and a piezoelectric actuator patch

In this study, nonlinear vibration of a conical shell with a piezoelectric sensor patch and a piezoelectric actuator patch is evaluated. The strain displacement relation is considered to be nonlinear and based on that the equations of motion and piezoelectric sensor output signal are extracted. For the first time, nonlinear electromechanical equations of motion for the conical shell with a piezoelectric sensor layer and a piezoelectric actuator layer are extracted in detail and presented. The producer of extraction of conical shell electromechanical equations of motions is presented for further clarifications. The output signal of the piezoelectric sensor patch considering the nonlinear strain displacement equation of motion is derived. For controlling the vibration actively, a proportional controller is defined by which the applied actuator signal is determined. The nonlinear electromechanical equations of motion are expanded based on conical shell strains. By applying the Galerkin method, the nonlinear time-domain equations are extracted. The complicated attained equations are solved using the harmonic balance method. Conical shell nonlinear frequency response in uncontrolled condition and controlled condition is computed and compared with each other. The frequency response shows that the active vibration control of the conical shell increases the nonlinearity of the system and reduces the vibration amplitude. In addition, free nonlinear vibration of the proposed system is calculated and presented. The results show higher impacts of piezoelectric patches on the conical shell free vibration response and they can reduce the vibration amplitude dramatically.

Active feedforward control of flexural waves in an Acoustic Black Hole terminated beam

Acoustic Black Holes (ABHs) are structural features that are typically realised by introducing a tapering thickness profile into a structure that results in local regions of wave-speed reduction and a corresponding enhancement in the structural damping. In the ideal theoretical case, where the ABH tapers to zero thickness, the wave-speed reaches zero and the wave entering the ABH can be perfectly absorbed. In practical realisations, however, the thickness of the ABH taper and thus the wave-speed remain finite. In this case, to obtain high levels of structural damping, the ABH is typically combined with a passive damping material, such as a viscoelastic layer. This paper investigates the potential performance enhancements that can be achieved by replacing the complementary passive damping material with an active vibration control (AVC) system in a beam-based ABH, thus creating an active ABH (AABH). The proposed smart structure thus consists of a piezo-electric patch actuator, which is integrated into the ABH taper in place of the passive damping, and a wave-based, feedforward AVC strategy, which aims to minimise the broadband flexural wave reflection coefficient. To evaluate the relative performance of the proposed AABH, an identical AVC strategy is also applied to a beam with a constant thickness termination. It is demonstrated through experimental implementation, that the AABH is able to achieve equivalent broadband performance to the constant thickness beam-based AVC system, but with a lower computational requirement and a lower control effort, thus offering significant practical benefits.

Observer based sliding mode control for subsonic piezo-composite plate involving time varying measurement delay

In this study, an observer based sliding mode control (SMC) scheme is proposed for vibration suppression of subsonic piezo-composite plate in the presence of time varying measurement delay by using the piezoelectric patch (PZT) actuator. Firstly, the state space form of the subsonic piezo-composite plate model is derived by Hamilton’s principle with the assumed mode method. Then an state observer involving time varying delay is constructed and the sufficient condition of the asymptotic stability is derived by using the Lyapunov-Krasovskii function, descriptor method and linear matrix inequalities (LMIs) for the state estimation error dynamical system. Subsequently, a sliding manifold is constructed on the estimation space. Then an observer-based controller is synthesized by using the SMC theory. The proposed SMC strategy ensures the reachability of the sliding manifold in the state estimate space. Finally, the simulation results are presented to demonstrate that the proposed observer-based controller strategy is effective in active aeroelastic control of subsonic piezo-composite plate involving time varying measurement delay.

Vibration Modelling and Control Experiments for a Thin-Walled Cylindrical Rotor with Piezo Patch Actuation and Sensing

This paper describes a dynamic model formulation and control experiments concerning the vibration behaviour of a thin-walled cylindrical rotor with internal piezoelectric patch transducers. Model development, validation and controller design procedures were undertaken for an experimental rotordynamic system comprising a tubular steel rotor (length 0.8 m, diameter 0.166 m and wall-thickness 3.06 mm) supported by two radial active magnetic bearings. Analytical solutions for mode shapes and natural frequencies for free vibration were first derived using a shell theory model, and these used to construct a speed-dependent parametric model for the rotor structure, including piezo patch actuators and sensors. The results confirm that the developed shell theory model can accurately capture the rotating frame dynamics and accounts correctly for frequency splitting from Coriolis effects. The model is also shown to be suitable for active controller design and optimization. Model-based H2 feedback control using the rotor-mounted actuators and sensors is shown to achieve vibration suppression of targeted flexural modes, both with and without rotation.

A coupled efficient layerwise finite element model for free vibration analysis of smart piezo-bonded laminated shells featuring delaminations and transducer debonding

This paper presents a computationally efficient multifield finite element (FE) model for accurate analysis of smart composite and sandwich shells equipped with piezoelectric patch actuators and sensors, featuring multiple delaminations and transducer debonding. It employs a facet shell element with four physical nodes and one electric node, based on the third order zigzag theory approximations for displacements and a piecewise quadratic through-thickness variation for the electric potential. A hybrid point-least squares method recently proposed by the authors is extended to impose the condition of continuity of the nonlinear displacement field at the delamination, debonding, and patch fronts. The methodology is generic for multiple patch transducers, delaminations, and debonding, occurring at any arbitrary interface and in-plane locations. The model shows excellent accuracy in comparison with the coupled full-field 3D FE solutions, for the natural frequencies and complex global, local and hybrid mode shapes of delaminated smart composite shells and soft-core sandwich plates, with partially debonded actuators and sensors. The developed model will be of immense use for the design of active vibration control and structural health monitoring strategies for smart laminated shell-type structures featuring such damages.

Estimation of stress intensity factor reduction for a center-cracked plate integrated with piezoelectric actuator and composite patch

Active repair of a damaged structure using piezoelectric (PZT) actuators has played a significant role during the last two decades in reducing crack damage propagation in structures due to its electro-mechanical effect. Similarly, passive repair of damaged structures using composite materials has been widely used in recent years, and it has been divided into many types. In this paper, the hybrid repair of center-cracked plate using PZT actuators at the front of a plate and a composite patch at the back of the plate is analytically and numerically investigated. First, the solution is obtained from Rose's equations for the center-cracked plate integrated with a composite patch and a passive PZT actuator under uniform uniaxial load. Second, the stress intensity factor (SIF) for a center-cracked plate due to stress produced by a PZT actuator is analytically modeled using the weight functions method. The superposition principle is then used to superimpose the aforementioned solutions in order to yield the PZT actuator and composite patch's hybrid stress intensity factor for the center-cracked plate. Finally, the proposed analytical method was verified using the finite element method. The results demonstrate low relative errors between the analytical and the FE of below 5% in all the cases studied in this paper.