Polyvinylidene Fluoride Actuators Research Articles

Optimal Vibration Control of Membrane Structures with In-Plane Polyvinylidene Fluoride Actuators

Different kinds of membrane structures have been proposed for future space exploration and earth observation. However, due to the low stiffness, high flexibility, and low damping properties, membrane structures are likely to generate large-amplitude (compared to the thickness) vibrations, which may lead to the degradation of their working performance. In this work, the governing equations are established at first, taking into account the modal control force induced by the polyvinylidene fluoride (PVDF) actuator. The optimal vibration control of the membrane structure is explored subsequently. A square PVDF actuator is attached on the membrane to achieve the vibration suppression. The influence of actuator position and control gains on the vibration control performance are studied. The optimal criteria for actuator placement and energy allocation are developed. Several case studies are numerically simulated to demonstrate the validity of the proposed optimization criteria. The analytical results in this study can serve as guidelines for optimal vibration control of membrane structures. Additionally, the proposed optimization criteria can be applied to active control of different flexible structures.

Nonlinear vibration control effects of membrane structures with in-plane PVDF actuators: A parametric study

In recent years, with the increasing use of membrane structures in space applications, the problems of large-amplitude (compared to the thickness) vibrations arise; leading to the degradation of their working performance. It is challenging to control the large-amplitude vibrations of membranes due to the high flexibility, low damping, and strong geometrical nonlinearity. In this study, polyvinylidene fluoride (PVDF) actuators are considered to develop the active vibration control of a pre-tensioned Kapton membrane. The governing equations are established based on the geometrically nonlinear theory of plates, taking into account the modal control force induced by the actuators. To analyze the nonlinear dynamic characteristics of the membrane, the theoretical and approximate solutions of nonlinear frequencies of the membrane are obtained, and the discrepancies between the two solutions under different vibration amplitudes are discussed. Control performance for both free vibration and harmonic forced vibration of the membrane is numerically studied. A comprehensive parametric study is carried out to investigate the influences of different system parameters, including the pretension and the size of the membrane, and the position and number of the actuators, on the control performance. Analytical results indicate that the vibration of the membrane can be effectively suppressed with the appropriately laminated PVDF actuators. The results of this research can be extended to the active control of different gossamer space structures.

Design, fabrication and experimental studies of compliant flexure diaphragm for micro pump

This study reports the performance of piezo actuated compliant flexure diaphragm for micropump and MEMS application. To achieve the high performance of diaphragm at the low operating voltage compliant flexure diaphragm design is introduced. Very limited work has done on the diaphragms of micropump. Large numbers of mechanical micropumps have used plane diaphragms. The central deflection of diaphragm plays an important role in defining the micropump performance. The flow rate of mechanical type micropump strongly depends on the central deflection of diaphragm. In this paper compliant flexure diaphragms are designed for micropump to achieve higher deflection at lower operating voltage. Finite element analysis of compliant flexure diaphragm with single layer PVDF (Polyvinylidene fluoride) actuator is simulated in COMSOL. Compliant flexure diaphragms with a different number of flexures are analyzed. The central deflection of compliant flexure diaphragms is measured for driving voltages of 90V to 140V in 10 steps. The deflection of the compliant flexure diaphragm mainly depends on flexure width and length, the number of flexures in the diaphragm, PVDF thickness, diaphragm thickness and driving voltage. Use of compliant flexure diaphragm for micropump will reduce the mass and driving voltage of micropump. An attempt is made to compare the results of compliant flexure diaphragms with plane diaphragms. From the experimental results it is noticed that the compliant flexure diaphragm deflection is twice that of the plane diaphragm at same driving voltage. Deflection of three flexure and four flexure compliant diaphragms is 10.5µm and 11.5µm respectively at 140V.

Adaptive Shape Control for Thermal Deformation of Membrane Mirror with In-plane PVDF Actuators

Optical membrane mirrors are promising key components for future space telescopes. Due to their ultra-thin and high flexible properties, the surfaces of these membrane mirrors are susceptible to temperature variations. Therefore adaptive shape control of the mirror is essential to maintain the surface precision and to ensure its working performance. However, researches on modeling and control of membrane mirrors under thermal loads are sparse in open literatures. A 0.2 m diameter scale model of a polyimide membrane mirror is developed in this study. Three Polyvinylidene fluoride (PVDF) patches are laminated on the non-reflective side of the membrane mirror to serve as in-plane actuators. A new mathematical model of the piezoelectric actuated membrane mirror in multiple fields, (i.e., thermal, mechanical, and electrical field) is established, with which dynamic and static behaviors of the mirror can be analyzed. A closed-loop membrane mirror shape control system is set up and a surface shape control method based on an influence function matrix of the mirror is then investigated. Several experiments including surface displacement tracking and thermal deformation alleviation are performed. The deviations range from 15 μm to 20 μm are eliminated within 0.1 s and the residual deformation is controlled to micron level, which demonstrates the effectiveness of the proposed membrane shape control strategy and shows a satisfactory real-time performance. The proposed research provides a technological support and instruction for shape control of optical membrane mirrors.

Closed-loop control for deflection of cantilever beam based on hybrid photovoltaic/piezoelectric actuation mechanism

This paper proposes a novel non-contact closed-loop control model for the deflection of cantilever beam based on hybrid photovoltaic/piezoelectric actuation mechanism. The polyvinylidene fluoride (PVDF) piezoelectric actuator was driven under the photovoltage of lead lanthanum zirconate (PLZT) cera mic which was irradiated by ultraviolet light. The closed-loop control equations for the deflection of cantilever beam were derived based on the coupled multi-physics model of PLZT ceramic and the constitutive model of cantilever beam. According to the identified parameters obtained from the static experiments during illumination phase and light-off phase, the mathematical simulation for closed-loop control of the deflection of cantilever beam was conducted. Furthermore, the corresponding experiments based on the hybrid photovoltaic/piezoelectric actuation mechanism were carried out to verify the proposed control model. The simulation and experimental results show that the deflection of cantilever beam laminated with a PVDF actuator can successfully achieve the target value by applying the UV light to the PLZT ceramic using a simple on-off control method.

Active vibration suppression of membrane structures and evaluation with a non-contact laser excitation vibration test

To realize a vibration suppression of flexible structures like a membrane, our research focuses on introducing smart structures technology into the membrane structure. In this study, the membrane structure is composed of a vibration control system using a flexible Polyvinylidene fluoride (PVDF) film as an actuator. A non-contact vibration test system, which uses a high power Nd: YAG pulse laser for producing an ideal impulse excitation and laser Doppler vibrometers for measuring the response on the membrane, is employed to evaluate the vibration characteristics of the smart membrane structure. To confirm the effectiveness of the proposed method, using a flexible PVDF actuator installed on the membrane structure, control experiments with H ∞ control for reducing single mode and multiple modes vibration are conducted. In the results of the control experiments for single mode vibration suppression, a corresponding resonance peak is reduced by around 20 dB. In case of multiple modes vibration suppression, the first and second resonance peaks are reduced by 14 dB and 24 dB, respectively. This study demonstrates that the present control method using a flexible piezoelectric element and a non-contact vibration test system effectively suppress and evaluate the vibration responses of smart membrane structures.

Active vibration suppression of payloads with a conical isolator

This article focuses on active vibration isolation of a rigid payload using a conical shell isolator laminated with piezoelectric sensors and actuators. The payload is mounted on the top (minor end) of the conical shell isolator. The piezoelectric sensor is laminated on the inner surface, and the piezoelectric actuator is laminated on the outer surface of the conical shell. The macro-fiber composite piezoelectric material is utilized as the actuator to enhance control performance, and polyvinylidene fluoride actuators are used as a comparison. The mathematical model of the conical isolator and the payload is derived in terms of the sensing signal equation and the actuation equation. Then, the modal equations are transformed into the state-space form with sensing signal as the system output and modal control force as the system input. Linear quadratic controllers are designed for each independent mode. In case studies, axial vibration isolation of the payload is performed to characterize the performance of the conical isolator and the optimal controller.

Advances of Surface Control Methodologies for Flexible Space Reflectors

With the advances in deployable membrane technologies, the possibility of developing large, lightweight reflectors has greatly improved. However, to achieve the required accuracy, precision surface control is needed. The goal of this research was to investigate the feasibility of applying distributed polyvinylidene fluoride actuators and domain control on a flexible reflector and address some of the technical challenges. An analytical model of the integrated reflector–actuator system was developed. A Kapton reflector with polyvinylidene fluoride actuators was experimentally tested and compared with the model. A new least-squares control law is designed to ensure optimal solutions are derived in a rigorous manner when constraints are applied. The model is exercised using individually controlled polyvinylidene fluoride actuators on a large-scale reflector under thermal load. Although the results are promising with the large number of actuators applied, the major challenge is that it is unrealistic to have the same number of power supplies as actuators in actual applications. To resolve this issue, a new optimization methodology was developed, designated as the en masse elimination algorithm, which finds the global optimal solution that groups the actuators to match the limited number of power supplies and achieve minimum surface error.

Active Vibration Control of a Double-curved Shell with a Laminated Polyvinylidene Fluoride Actuator

The main objectives of this study are to establish a mechanical model of a double-curved shell partially covered by a laminated polyvinylidene fluoride actuator (LPA) and demonstrate its use in active control. The dynamic equations of a shallow shell with a much smaller LPA attached are derived first; The optimal position and dimensions of an LPA are then determined, based on formulae for the control forces derived. For an example of a shallow shell, significant control effect is obtained for frequencies below 2 KHz when a 4-layer LPA with optimized dimensions is adopted; The control effects of LPAs with different numbers of polyvinylidene fluoride (PVDF) layers are then explored, including with the results when the LPA at different positions and with different dimensions. The results indicate that a multi-layered LPA can control the vibration of a double-curved shell significantly with low control voltages and has advantages over point force actuators; The optimization approaches for the dimensions of the LPA and its position are practical and efficient.

A New Piezoelectric Actuator Induces Bone FormationIn Vivo: A Preliminary Study

This in vivo study presents the preliminary results of the use of a novel piezoelectric actuator for orthopedic application. The innovative use of the converse piezoelectric effect to mechanically stimulate bone was achieved with polyvinylidene fluoride actuators implanted in osteotomy cuts in sheep femur and tibia. The biological response around the osteotomies was assessed through histology and histomorphometry in nondecalcified sections and histochemistry and immunohistochemistry in decalcified sections, namely, through Masson's trichrome, and labeling of osteopontin, proliferating cell nuclear antigen, and tartrate-resistant acid phosphatase. After one-month implantation, total bone area and new bone area were significantly higher around actuators when compared to static controls. Bone deposition rate was also significantly higher in the mechanically stimulated areas. In these areas, osteopontin increased expression was observed. The present in vivo study suggests that piezoelectric materials and the converse piezoelectric effect may be used to effectively stimulate bone growth.

Numerical and experimental investigations of actuating characteristics of laminated polyvinylidene fluoride actuator used on paraboloidal shells

The effect of a laminated polyvinylidene fluoride (PVDF) actuator is analyzed when partially covering a paraboloidal shell. Models of control forces are established using the thin flexible shell theory and the membrane approximation. Analytical expressions of actuating forces and moments are derived and a parametric study is conducted to evaluate the effects of the physical properties of the actuator on the control forces. To verify the model, experiments were carried out on actuation and open-loop vibration control of a paraboloidal antenna with a much smaller actuator. The experimental results agree well with those obtained analytically. The results indicate the following: The laminated PVDF actuator (LPA) can provide effective control forces with low voltages. The control forces consist of actuating forces and moments, but the effect of the normal actuation force distribution is much greater than that of the actuation moments in controlling the normal vibration. The larger the curvature radius of the paraboliodal shell, the smaller the magnitudes of the required actuating forces. The magnitudes of actuating forces are approximately linear with the number of PVDF layers.

Experimental study of a smart foam sound absorber

This article presents the experimental implementation and results of a hybrid passive/active absorber (smart foam) made up from the combination of a passive absorbent (foam) and a curved polyvinylidene fluoride (PVDF) film actuator bonded to the rear surface of the foam. Various smart foam prototypes were built and tested in active absorption experiments conducted in an impedance tube under plane wave propagation condition at frequencies between 100 and 1500 Hz. Three control cases were tested. The first case used a fixed controller derived in the frequency domain from estimations of the primary disturbance at a directive microphone position in the tube and the transfer function between the control PVDF and the directive microphone. The two other cases used an adaptive time-domain feedforward controller to absorb either a single-frequency incident wave or a broadband incident wave. The non-linearity of the smart foams and the causality constraint were identified to be important factors influencing active control performance. The effectiveness of the various smart foam prototypes is discussed in terms of the active and passive absorption coefficients as well as the control voltage of the PVDF actuator normalized by the incident sound pressure.

The Analysis of Structural–Acoustic Coupling of an Irregular Enclosure Under the Excitation of Point Force and PVDF

The physical model of this paper is an irregular enclosure with double flexible plates. The primary source is the vibration of Plate A excited by a point force. The secondary source is the vibration of Plate B excited by a polyvinylidene fluoride (PVDF) actuator. First, the interaction of the PVDF actuator and a thin plate is analyzed and the distribution of strain and stress is gained. Based on the hypothesis of linear distribution of strain on two sections of the plate–film system, a formula is deduced to calculate the rate of the strain distribution. Then an experiment is proposed to test the sound pressure response in an irregular enclosure under the excitation of the PVDF actuator. Second, the theoretical formulas of the mode contributions of the two plates and the cavity are deduced. Then the formulas are converted into compact matrix equations. Thus the expression of sound response of one point in the enclosure is gained under the excitation of both the primary and the secondary sources. Based on these results, the sound pressure square is taken as the control aim function. At last the optimized curves of control voltage and control phase are achieved.

직접속도 피드백을 이용한 지능판의 능동구조음향제어

This paper presents a study of low frequencies volume velocity vibration control of a smart panel in order to reduce sound transmission. A distributed piezoelectric quadratically shaped polyvinylidene fluoride (PVDF) polymer film is used as a uniform force actuator and an array of <TEX>$4\;{\times}\;4$</TEX> accelerometer is used as a volume velocity sensor for the implementation of a single-input single-output control system. The theoretical and experimental study of sensor-.actuator frequency response function shows that this sensor-actuator arrangement provides a required strictly positive real frequency response function below about 900 Hz. Direct velocity feedback could therefore be implemented with a limited gain which gives reductions of about 15 dB in vibration level and about 8 dB in acoustic power level at the (1,1) mode of the smart panel. It has been also shown that the shaping error of PVDF actuator could limit the stability and performance of the control system.

Spatial aperture shading of polyvinylidene fluoride applied to distributed systemsfor uniform damping control

This paper introduces a model for a vibration control system in which spatiallyetched polyvinylidene fluoride (PVDF) was utilized to implement uniformdamping control on a distributed system. Uniform damping node control(UDNC) theory states that near optimal vibration control can be achievedwhen the following criteria are met: all modes are damped at the sameexponential decay rate, the open-loop and closed-loop natural frequencies of thestructure are identical and the closed-loop modal shapes are identical tothe open-loop modal shapes. To help accomplish this, in a system withN modesparticipating in a response, sensor/actuator pairs are placed at the nodes of theN + 1modes. Spatially shaded PVDF actuators are distributed actuators that producepseudo-discrete forces due to the special weighting applied to the etchedelectrodes. The system was demonstrated using a spring steel cantilevered beamand spatially etched PVDF actuators that were placed according to nodalcontrol theory. When given the set of gains that are attributed to UDNC,the modes de-couple, reducing spillover. This experiment marks the firsttime that uniform damping control has been realized experimentally.

Coupling analysis of a matched piezoelectric sensor and actuator pair for vibration control of a smart beam.

This paper presents a theoretical and experimental study of the in-plane and out-of-plane coupling of a matched piezoelectric sensor/actuator pair bonded on a beam. Both the sensor and actuator are triangularly shaped polyvinylidene fluoride (PVDF) transducers and are intended to provide a compact sensor/actuator system for beam vibration control. The measured sensor-actuator frequency response function has shown an unpredicted increase in magnitude with frequency, which was found, to be due to in-plane vibration coupling. An analytical model has been developed to decompose the sensor-actuator response function into an in-plane contribution and an out-of-plane contribution. This in-plane coupling can limit the feedback control gains when a direct velocity feedback control is applied. A method called the j omega s compensation method is proposed to identify the effect of the in-plane vibration coupling at low frequencies. Even after this compensation, however, there was unexpected strong out-of-plane coupling at even modes, which may have been caused by a lack of accuracy in the shaping of the PVDF sensor and actuator. Numerical simulations have confirmed the sensitivity of the matched sensor/actuator pair with shaping errors.

Sensor/Actuator Optimal Design for Active VibrationControl of Shell Structure

In this paper, a distributed sensor and actuator are designed for the active vibration control of shell structure. To prevent the adverse effect of spillover, distributed modal sensorlactuator system is established by optimizing the electrode pattern and the lamination angle of polyvinylidene fluoride (PVDF). Finite element programs are developed to consider the curved structures integrated with PVDF sensor and actuator. The nine-node Mindlin shell element is used for finite element discretization. The electrode pattern and the lamination angle of PVDF sensor/actuator are optimized using genetic algorithm. The sensor is designed to minimize the observation spillover. and actuator is designed to minimize the system energy of the control modes under a given initial condition. For the verification of the design, numerical simulation and real-time vibration control experiment ofthe integrated smart structure are performed using discrete LQG method as the control law. A singly curved cantilevered smart shell structure integrated with distributed modal sensor/actuator for the suppression of the first and second modes is manufactured for the experiment. The vibration suppressions of control modes are successfully achieved as expected.

Shape measurement and control of deployable membrane structures

The shape inaccuracies of inflatable antennas and the potential shape control of the surface of those structures are investigated. Surface shape inaccuracies are due to geometric nonlinear deformation. Correcting the shape of these inflatables focused on the integration of piezopolymer actuators on the membranes. The out-of-plane displacements of a membrane structure were assessed with the shadow moire method. The experimentally measured shape of the structure confirmed the extent of deviation from the ideal optical surface, a paraboloid of revolution. Active control of the shape of the membrane was tested using a piezoelectric material, polyvinylidene fluoride (PVDF). The deformation caused by actuation of the membrane structure was evaluated using electronic speckle pattern interferometry. An analytical solution was developed to verify the extent of shape correction that can be achieved by embedded PVDF actuators. It was confirmed that micron-level shape corrections are possible for future space-based sensors that use inflatable antennae technology.

Anisotropic effects of polyvinylidene fluoride on the control of transmitted sound fields through a composite plate

This paper presents numerical simulations on the control of sound transmission through a composite plate. The composite plate mounted in an infinite baffle is excited by the incident plane wave. The anisotropic PVDF (polyvinylidene fluoride) films bonded on the surface of the plate are used as distributed actuators for the reduction of sound transmission. The vibration of composite the plate and the sound transmission through the plate are analysed by using the coupled finite element and boundary element method. A constrained minimization problem was solved to obtain input voltages of the piezoelectric actuators, so that the transmitted sound can be reduced. To investigate the effects of anisotropic PVDF, several distributed PVDF actuators are tested in a control simulation. The results show that the control effectiveness of distributed PVDF actuators can be enhanced by utilizing the distributed shape and the directional characteristics of PVDF. Then the design of a PVDF actuator that is efficient for the control of sound transmission is performed by optimizing the shape and the ply angle of PVDF. It is shown that the reduction of sound transmission through the plate is successfully achieved, if the distributed shape and the ply angle of the PVDF actuator are properly selected.

Electrode Pattern Design of Piezoelectric Sensors and Actuators Using Genetic Algorithms

A distributed piezoelectric sensor and actuator have been designed for the efficient vibration control of a plate. Optimization of the electrode pattern of polyvinylidene fluoride (PVDF) film has been performed to realize the concept of modal transducer for a two-dimensional structure. The finite element method is used to model the structure that includes the PVDF sensor and actuator. Various lamination angles of transducers are taken into consideration to utilize the anisotropy of the PVDF film, The electrode pattern over the entire surface of the plate is determined by deciding on or off of each electrode segment. The actuator design is based on the criterion of minimizing the system energy in the control modes under a given initial condition. The sensor is designed to minimize the observation spillover, Modal control forces for the residual (uncontrolled) modes have been minimized during the sensor design. A genetic algorithm, which is suitable for this kind of discrete problem, has been utilized for optimization. A discrete linear quadratic Gaussian control law has been applied to the integrated structure for real-time vibration control. The performance of the sensor, the actuator, and the integrated smart structure has been demonstrated by experiments.