THUNDER Actuators Research Articles

Modeling and design of a high-performance hybrid actuator

This paper presents the model and design of a novel hybrid piezoelectric actuator which provides high active and passive performances for smart structural systems. The actuator is composed of a pair of curved pre-stressed piezoelectric actuators, so-called commercially THUNDER actuators, installed opposite each other using two clamping mechanisms constructed of in-plane fixable hinges, grippers and solid links. A fully mathematical model is developed to describe the active and passive dynamics of the actuator and investigate the effects of its geometrical parameters on the dynamic stiffness, free displacement and blocked force properties. Among the literature that deals with piezoelectric actuators in which THUNDER elements are used as a source of electromechanical power, the proposed study is unique in that it presents a mathematical model that has the ability to predict the actuator characteristics and achieve other phenomena, such as resonances, mode shapes, phase shifts, dips, etc. For model validation, the measurements of the free dynamic response per unit voltage and passive acceleration transmissibility of a particular actuator design are used to check the accuracy of the results predicted by the model. The results reveal that there is a good agreement between the model and experiment. Another experiment is performed to teste the linearity of the actuator system by examining the variation of the output dynamic responses with varying forces and voltages at different frequencies. From the results, it can be concluded that the actuator acts approximately as a linear system at frequencies up to 1000 Hz. A parametric study is achieved here by applying the developed model to analyze the influence of the geometrical parameters of the fixable hinges on the active and passive actuator properties. The model predictions in the frequency range of 0–1000 Hz show that the hinge thickness, radius, and opening angle parameters have great effects on the frequency dynamic responses, passive isolation characteristics and the locations of their peaks and dips. Furthermore, the output actuating force can be improved by increasing the hinge hardness, which is controlled by its dimensions, although increasing the hinge hardness may cause a decrease in the free displacement and passive insulation performance, particularly at low frequencies.

Integrated Localized MicroCooling Using High-Displacement Piezoelectric Actuators

RF communication and radar systems present an extreme thermal management challenge. These systems are comprised of tightly packaged, high-power components requiring a controlled temperature to meet performance and reliability parameters. In these systems, there is little space available for macro-scale air flow or other traditional cooling methods. In addition, heat generating components are typically microscale semiconductor devices fabricated on integrated circuit substrates buried deeply within the system. Localized cooling using integrated microsystems may provide a solution to these thermal management issues. One approach is the integration of miniature synthetic air jets near the heat generating components. Synthetic jets are generated using oscillating piezoelectric actuators that force air through a small nozzle at high flow rates and in close proximity to the heat generating component. The resulting jets provide vorticity within the fluid, leading to enhanced mixing with the surrounding lower temperature environment and a subsequent increase in the heat transfer coefficient. The US Army AMRDEC has been developing and operating microactuator test beds, utilizing high-displacement actuator architectures, including THUNDER and Lightweight Piezo-Composite Actuator (LIPCA) approaches, to reduce actuator size while maintaining sufficient flow rates and vorticity. This investigation has modeled and fabricated potential high-displacement miniature actuators, as well as predicted and characterized resulting jet parameters and heat transfer coefficients utilizing these actuators. This paper will present actuator designs, fabrication process, and cooling results using these high-displacement piezoelectric actuators as the drive element.

Design of a scaled wind turbine with a smart rotor for dynamic load control experiments

AbstractThe ever increasing size of wind turbines poses a number of design issues for the industry, like increasing component mass and fatigue loads. An interesting concept for reducing fatigue loads is the implementation of spanwise distributed devices to control the aerodynamic loading along the span of the blade, thus mitigating fluctuations in loading and adding damping to the blade modes. This is usually referred to as the smart rotor concept. In the design of such a rotor, as compared to a traditional one, the integration of sensors and actuators poses additional design challenges. In the research discussed in this paper, a scaled smart rotor was designed and constructed to study its fatigue load reduction potential. A 1.8 m diameter rotor was manufactured and equipped with trailing‐edge flaps. The flaps were based on piezo electric Thunder actuators that allow for high‐frequent actuation. The dynamic strain behaviour of the blade was analysed for optimal placement of the sensors. Several sensors that record the strains and accelerations at different locations along the blade were implemented, but the controller was based on a piezo electric strain sensor. The rotor blades were mounted on a small turbine in the Delft University's Open Jet Facility wind tunnel and a mathematical state space model was obtained by using dedicated system identification techniques. Single‐Input Single‐Output, Multi‐Input Multi‐Output ℋ︁∞ feedback and feedforward controllers were designed, each focusing on different parts of the load spectrum. The rotor was tested at 0 and 5° yaw angles, with and without load control. A significant reduction of the dynamic loads was attained. Copyright © 2010 John Wiley & Sons, Ltd.

Fabrication and characterization of THUNDER actuators—pre-stress-induced nonlinearityin the actuation response

This paper documents an experimental and theoretical investigation into characterizing themechanical configurations and performances of THUNDER actuators, a type ofpiezoelectric actuator known for their large actuation displacements, throughfabrication, measurements and finite element analysis. Five groups of such actuatorswith different dimensions were fabricated using identical fabrication parameters.The as-fabricated arched configurations, resulting from the thermo-mechanicalmismatch among the constituent layers, and their actuation performances werecharacterized using an experimental set-up based on a laser displacement sensor andthrough numerical simulations with ANSYS, a widely used commercial softwareprogram for finite element analysis. This investigation shows that the presenceof large residual stresses within the piezoelectric ceramic layer, built up duringthe fabrication process, leads to significant nonlinear electromechanical couplingin the actuator response to the driving electric voltage, and it is this nonlinearcoupling that is responsible for the large actuation displacements. Furthermore, theseverity of the residual stresses, and thus the nonlinearity, increases with increasingsubstrate/piezoelectric thickness ratio and, to a lesser extent, with decreasing in-plane dimensions of thepiezoelectric layer.

A simple sensor model for THUNDER actuators

A quasi-static (low frequency) model is developed for THUNDER actuators configured asdisplacement sensors based on a simple Raleigh–Ritz technique. This model is used tocalculate charge as a function of displacement. Using this and the calculated capacitance,voltage versus displacement and voltage versus electrical load curves are generated andcompared with measurements. It is shown that this model gives acceptable results and isuseful for determining rough estimates of sensor output for various loads, laminateconfigurations and thicknesses.

Structurally Graded Monolithic Piezoelectric Actuators, Modeling and Optimization with FEM

In this work, novel structurally graded piezoelectric disc actuators are proposed. The monolithic gradient actuators had nonuniform thickness profiles, which caused distribution of the electric field and resulted in bending of the discs. The geometry and clamping conditions of the actuators were varied and the displacement properties were optimized using ATILA and Comsol Multiphysics finite element modeling (FEM) softwares. The material parameters of commercial PZT-5H were used in the modeling of the actuators — 25 mm in diameter with an original thickness of 0.5mm. Additional steel layers with different thicknesses were introduced under the actuators in `unimorph-fashion' in order to study their effect on the displacements and stresses of the actuators. The modeling results showed that the bending of the monolithic actuators could be realized without any additional passive layers and also that the utilization of clamping further improved the displacement capabilities. For example, ~53 μm axial displacements were enabled with a 1 V/μm electric field (corresponding to the thinnest part of the actuator) without any passive layers. The modeled displacement results were comparable to displacements obtained by pre-stressed PRESTO (~50 μm), THUNDER (~60 μm) and RAINBOW (~70 μm) actuators of 25 mm in diameter with a 1 V/μm electric field.

A Comparison of the Deformations of Various Piezoceramic Actuators

Presented are the predicted manufactured shapes and actuated shape changes of metal-based THUNDERTM-like actuators and fiber-reinforced-polymer-based LIPCA-C1-and LIPCA-C2-like actuators. As these actuators, which are laminated in nature, are manufactured flat at an elevated temperature and then cooled for use, they deform out of plane as they cool, resulting in residual curvatures. The development of the residual curvatures are predicted with a 23-term Rayleigh-Ritz model based on energy principles. Because of the large out-of-plane deformations due to cooling, geometrically nonlinear effects, in the sense of von Karman, are included. Actuated curvatures due to activation of the piezoceramic material are also predicted. The behaviors of plate and beam-like actuator geometries over a range of sidelength-to-thickness ratios are investigated. Finite element results for selected geometries are presented for comparison with the 23-term model. The results show that geometrically nonlinear effects are quite strong for THUNDER and LIPCA-C2 plate-like actuators, resulting in the potential for more than one cooled shape for THUNDER actuators and of a sudden change in the actuated shape, referred to here as snap-through, for LIPCA-C2 actuators. For the LIPCA-C1 actuators, and the beam-like geometries of the other two actuators, geometrically nonlinear effects are not as strong. Residual stress predictions within the cooled and activated actuators are also presented. Though the actuators considered are specific in design, the results can be interpreted more generally and point to the fact that a wide range of behaviors can be expected from geometrically nonlinear effects interacting with variations in materials (i.e., metals vs. fiber-reinforced materials) and geometry (i.e., platelike vs. beam-like and sidelength-to-thickness ratio).

Poling Conditions of Pre-Stressed Piezoelectric Actuators and Their Displacement

The poling procedure has always been the key issue in producing piezoelectric actuators with optimised performance. This is also true with the relatively new category of pre-stressed bender actuators, where mechanical bias achieved with a passive layer is introduced in the actuators during manufacturing. Due to these factors, the behaviour of the actuator under poling is different compared to its bulk counterparts. In this paper, two different thicknesses of commercial PZT 5A and PZT 5H materials were used in bulk actuators and pre-stressed benders realised by new method. Pre-stress was introduced by using a post-fired biasing layer utilising sintering shrinkage and difference in thermal expansion. The hysteresis loop of the actuators was measured under 0.5–7.0 MV/m electric fields at 25–125∘C temperatures, providing information about their remnant polarisation and coercive field before poling. The results showed that high electric field and 25∘C temperatures in poling provided higher remnant polarisation and coercive electric field than using 125∘C temperature at poling. Difference was especially significant in coercive electric field values where up to 114.8% difference was obtained for PZT 5H bulk actuator and 65.9% for pre-stressed actuators. Higher coercive fields can be utilized as increased operating voltage range of piezoelectric devices. The differences in results obtained here and by others can be explained by the different pre-stress level, stronger clamping of the thicker passive layers of the RAINBOW and THUNDER actuators and passive ring area introducing high tensile stresses. The same conditions were used to pole the actuators, after which the displacement and dielectric constant of the actuators were measured. The displacement measurements showed that remnant polarisation has good correlation with displacement. This fact can be used in estimating pre-stressed actuator performance before actual poling. The dielectric constant measurements with a small signal after poling gave even better correlation than the remnant polarisation.

THE CORRELATION OF ELECTRICAL PROPERTIES OF PRESTRESSED UNIMORPHS AS A FUNCTION OF MECHANICAL STRAIN AND DISPLACEMENT

ABSTRACT Prestressed Unimorph-type actuators are being adapted for industrial applications previously not envisioned for piezoelectric based technology. These include electronically controlled diesel valve injectors, non-resonance fluidic pumps and low-stroke linear motors. To expand the range of applications and refine the design of these actuators for additional technologies, the effects of load placement, force distribution and mounting must be investigated in order to retrofit existing devices and systems. This research uses several sets of multi-strain gauged THUNDER actuators mounted in a fully compliant test fixture equipped with an LVDT and weight system and to characterize the room temperature strain and displacement as a function of mechanical loading. The results will be used to refine computational models that aid in the design of these actuators for future applications.

Modeling and control of power flow in a double-beam system

The vibrational power flow in a double-beam system is investigated theoretically and experimentally in this paper. A novel large displacement piezoelectric actuator assembly, comprising two curved THUNDER actuators, is used to connect the two beams and provide both passive and active isolation at the same time. A simulation model is proposed to describe the coupled mechanical and electrical properties of the new actuator assembly. Modal expansion approach is used to study the power transmissions between the two beams which are mechanically and electrically coupled via the actuator mounts. The effectiveness of both active and passive isolation has been investigated. The optimal control voltage for each actuator is obtained by minimizing the time-averaged power transmitted into the receiver beam. Results show a significant reduction in vibration power transmission. A correlation between the control effort and the mode shapes to be controlled is shown to exist.

Piezoelectric Actuator–Sensor Analysis using a Three-Dimensional Assumed Strain Solid Element

This paper presents a piezoelectric solid element that can be used for modeling thin sensors and actuators. The element has been extended from an eighteen-node assumed strain solid element that can alleviate locking in mechanical problems. For the fully coupled mechanical-piezoelectric formulation, the electric potential is regarded as a nodal degree of freedom in addition to three translations in the original element. Consequently, the induced electric potential can be calculated for a prescribed load and the actuation displacement computed for an input voltage. Since the assumed strain solid element can relieve locking, the proposed element can also be used to analyze the behavior of very thin actuators. In addition, a finite element code was developed based on the proposed formulation and typical numerical examples were solved for code validation. Parametric studies for the THUNDER actuator have been also conducted using the code, where specific combinations of materials used for the layers plus the curvature of THUNDER were both found to improve the actuation displacement.

Experimental and analytical study of active control of energy transmission through double walls using novel piezoelectric actuators

Active noise control has recently been used to increase the sound transmission loss of double wall structures. Vibration energy transmission through a double-plates system is investigated experimentally and analytically in this paper. Novel high performance actuators which use two curved THUNDER actuators as active driving components are developed and mounted between the two plates to control the energy transmission in the double-plates system. The Rayleigh–Ritz method and eigenfunction expansion theorem are used to resolve arbitrary boundary conditions of plates, and the feedforward control strategy is employed in this paper. The time average power transmission between the source, actuators and receiver plate are discussed and utilized as a cost function to obtain optimal control. The optimal control voltages for actuators are obtained by minimizing the cost function. A double-plates system connected by four actuators is set up experimentally in order to verify the models and formulations by comparing with analytical results. The analytical and experimental data show that the new actuator exhibits excellent performance on active control of power transmission.

A feasibility study of active vibration isolation using THUNDER actuators

The ‘thin layer composite unimorph piezoelectric driver and sensor’ (THUNDER)piezoelectric actuator is a newly developed active control device that possessesmany advantages over other conventional piezoelectric actuators. Particularly, itscapacity for generating high displacement and its inherent flexibility make it anideal candidate in applications for active vibration isolation. In this paper, wefocus on the simulation, design and experimental tests of a hybrid isolation systemby taking advantage of both the passive and active effects provided byTHUNDER actuators. Different aspects concerning its practical use are firstinvestigated. Then its dynamic properties are modelled using a mechatronicapproach. From there a dynamic model is established considering the parameterevolution due to the mass loading. Finally a simple prototype is designedusing three THUNDER actuators. Both simulation and experimental testsshow the potential of THUNDER actuators in active vibration controlapplications.

3 차원 가정변형률 솔리드 요소를 이용한 압전 작동기/감지기 해석

본 논문에서는 18절점 가정 변형률 솔리드 요소를 이용하여, 기계적 물리량과 전기적 물리량이 완전히 연성된 정적 문제를 해석할 수 있는 유한요소 정식화 과정을 유도하였다. 요소 결점의 축방향 변위 자유도 외에 전기 자유도를 추가하여 주어진 변위와 하중에 의해 발생하는 유도전압을 계산할 수 있다. 또한 가정 변형률 요소를 사용함으로써 박판형 구조물을 모델할 때 발생할 수 있는 잠김현상을 해소하였다. 유도된 유한요소 정식을 바탕으로 프로그램을 작성하였으며, 몇가지 수치예제에 적용하여 작성된 코드를 검증하였다. 본 요소를 이용하여, 여러 가지 변수가 THUNDER의 작동변위에 미치는 영향을 분석하였다. 이를 통하여, 특정한 재료와 곡률을 갖출 경우 THUNDER의 작동성능이 향상됨을 확인하였다. The paper deals with a fully assumed strain soild element that can be used for modeling of thin sensors and actuators. To solve fully coupled field problems, the eledtric potential is regarded as a nodal degree of freedom in addition to three translations in an eighteen node assumed strain soild element. Therefore, the induced electric potential can be calculated for a prescribed load and the actuation displacement can be computed for an input voltage. Since the assumed strain solid element can alleviate locking. A finite element code is developed based on the formulation and typical numerical examples are solved for code validation. Using the code, we have conducted parametric study for THUNDER actuator. It is found that a particular combination of materials for layer curvature of THUNDER improves the actuation displacement.

Analysis and design of doubly curved piezoelectric strip-actuated aperture antennas

Aperture antennas that have the ability to change their reflector shape through the use of piezoelectric actuators have been studied. The results show that those antennas can exhibit beam steering and beam shaping in the far field. However, many of the previous studies have been confined to cylindrical shape antennas. This study examines the use of doubly curved antenna structures to achieve better performance in controlling an antenna's coverage area. The spherical antenna is modeled as a shallow spherical shelf with a small hole at the apex for mounting. Following Reissner's (1959) approach, a stress function is introduced and two governing equations are derived in terms of the stress function and the axial deflection. Next, the surface deflections are evaluated from the calculated stress function and the axial deflection. As actuators, four lead-zirconate-titanate (PZT) thunder actuators are attached along the meridians separated by 90/spl deg/, respectively. The forces developed by the actuators are expanded in a Fourier series and fed into the governing equations as boundary conditions at the outer edge. Finally, the deflection versus applied voltage is calculated analytically and its effect on the far-field-radiation is given.

Mechatronic design and control of singly and doubly curved composite mesoscale actuator systems

Recently, the design of curved mesoscale actuators (deflections from 1 to 15 mm) has been a topic of study for many researchers. The work in this paper deals with the development of a comprehensive modeling technique for dealing with curved actuators. First, the formulation begins with the equations of motion for a general shell surface. Second, relationships for reducing the equations to those for known actuators are given. The technique can be applied to a broad array of curved actuators. These actuators include but are not limited to rainbow actuators, thunder actuators, and basic C-block actuators. Next, the technique is then experimentally verified on a stack of rainbow actuators. Finally, the system is controlled using both classical and intelligent control techniques. In addition, hardware and circuitry issues are explored.

Modeling and Control of a Singly Curved Active Aperture Antenna Using Curved Piezoceramic Actuators

There is an increasing need for aperture antenna devices that incorporate multifunctional capability. One popular solution to this problem is the use of an “active aperture antenna” that is able to vary the direction and shape of its radiation pattern by using actuators to alter the shape of the reflector. This study focuses on the use of a pre-curved piezoceramic actuator, referred to as a THUNDER actuator, to change the shape of a prototype reflector. These actuators offer greater force, deflection and higher strength than traditional PZT actuators, while maintaining cost effectiveness. In this study the design of a prototype antenna structure that can accommodate deflection experiments and far-field radiation pattern tests is presented. The theoretical relationship between the dish deflection and the input voltage is established in two stages. In the first stage, the deflection at the end of the actuator is determined using a combination of Hamilton’s principle and laminated composite curved beam theory. The piezoelectric properties of the actuator are also considered during this stage. In the second stage, the deflection at the tip of the dish is calculated using geometric relationships, with the assumption that the remaining portion of the dish moves as a rigid body. The resulting deflection equations yield results that closely match the experimental quasi-static deflection results for a given input voltage, despite the presence of hysteresis. A dynamic model for a THUNDER actuator is developed based on experimental frequency response measurements. Positive Positioned Feedback (PPF) control is implemented on the system, in order to reduce position overshoot and oscillations in the transient response of the structure. The controller yields an improvement in the transient response in both simulation and experiments. Finally, the controlled system is utilized to transmit radiation in the far field.

Real-time feedforward control of low-frequency interior noise using shallow spherical shell piezoceramic actuators

This paper demonstrates the use of RAINBOW and THUNDER actuators as acoustic control sources in the real-time control of low frequency harmonic interior noise. The former actuator drives a flat acoustic piston while the latter drives a conventional speaker cone. The low-profiled and lightweight nature of these actuators makes them suitable for aircraft applications. The two devices have been used successfully for active noise cancellation inside a duct and a cylindrical enclosure. This paper presents results of the real-time noise control experiments.

Piezoelectrically driven speakers for active aircraft interior noise suppression

This paper presents results from an experimental study of light weight piezoelectrically driven speakers developed in the Smart Trim Technology Laboratory (SMARTTLAB) at University of Delaware. The speakers are of direct radiator type and are driven by shallow spherical shell piezoceramic actuators. Two implementations – an acoustic piston and a cone – have been tested. Results from small signal characteristics measurements performed in a semi-reverberant environment are presented. While most of the tests have been performed using RAINBOW actuators as driving elements, some results for the THUNDER actuator are also presented. The possible use of these devices as controllable acoustic sources in active noise control applications is discussed. The low weight of these actuators makes them highly suitable for aircraft interior noise control applications with severe space and weight restrictions.