This research seeks to develop a novel branch of materials systems called Distributed Intelligent Materials Systems
(DIMS) which incorporate actuation, sensing, electronics and intelligence as inherent parts of the material structure. A
microcantilever optical switch is fabricated as a concept demonstrator with Gallium nitride (GaN) as host material. GaN
has several material characteristics which enable it to outperform other semiconductor materials for electronic
applications. It also displays exceptional chemical inertness, has a relatively high piezoelectric coefficient, good
mechanical strength and toughness and is transparent to wavelengths in the visible spectrum. In this paper we develop
and fabricate a GaN-based, piezoelectrically actuated microcantilever optical switch/waveguide. While the GaN-material
offers the benefits mentioned above, the piezoelectric actuation and the cantilever design provide benefits of lighter
weight, compactness, speed of actuation, reduced structural complexity enabling easier fabrication and low wear and tear
due to minimal moving parts. The proposed design has a conventional unimorph configuration with GaN actuated in d31
mode. In this configuration, a laminar metal electrode and a doped n-type GaN layer are used to apply an electric field in
the top layer to actuate the unimorph. The unimorph is fabricated as a micro-cantilever by using surface micromachining
methods on epitaxial GaN grown on a GaN substrate. The cantilever is then etched partially using conventional
semiconductor processing techniques and using a recent microfabrication technique known as photoelectrochemical
(PEC) etch. PEC etching enables the fabrication of MOEMS structures that are rather difficult to create using conventional methods. Novel modifications and improvements to the current state-of-the art in PEC for GaN are presented and discussed.
In this paper, information on the various aspects of smart materials is compiled in an easy-to-consult format by conducting extensive survey of published articles and including the properties of the materials. The compilation of a comprehensive database on smart materials enables to expedite a material selection process in the design of smart material devices or systems. We show the compiled database in a legible format such as GUI based computer software that determines and simulates what material to use based on properties and performance. Finally, the associated system-level models for selected materials are developed and shown in the compilation.
Proc. SPIE. 7645, Industrial and Commercial Applications of Smart Structures Technologies 2010
KEYWORDS: Model-based design, Control systems, Detection and tracking algorithms, Digital filtering, Electronic filtering, Nonlinear control, Systems modeling, Actuators, Signal attenuation, Modulation
This research investigates a supporting structure with smart struts under a vibratory load. In the case of most rotorcraft,
structure-borne noise and vibration transmitted from the gearbox contains multiple spectral elements and higher
frequencies, which include gear mesh frequencies and their side bands. In order to manage this issue, significant research
have been devoted to active smart struts which have tunable stiffness such that a higher level of attenuation is possible.
However, present techniques on active control are restricted mostly to the control of single or multiple sinusoids and thus
these are not applicable to manage modulated and multi-spectral signals. Therefore, enhanced control algorithms are
required in order to achieve simultaneous attenuation of gear mesh frequencies and their side bands. Proposed algorithms
employing two nonlinear methods and one model-based technique are examined in this study. Their performance is
verified by comparing with conventional algorithms. Moreover, these algorithms are implemented to exhibit whether
they are feasible to narrowband or broadband control through experiments with a single smart strut. Novel
methodologies are expected to be applied to several active vibration and noise control practices such as vehicles and
other engineering structures.
The primary objective of this research is to develop novel model-based multispectral controllers for smart material
systems in order to deal with sidebands and higher harmonics and with several frequency components simultaneously.
Based on the filtered-X least mean square algorithm, it will be integrated with a nonlinear model-based controller called
model predictive sliding mode control. Their performance will be verified in simulation and with various applications
such as helicopter cabin noise reduction. This research will improve active vibration and noise control systems used in
engineering structures and vehicles by effectively dealing with a wide range of multispectral signals.
Ferroelectrics in microwave antenna systems offer benefits of electronic tunability, compact size and light weight, speed
of operation, high power-handling, low dc power consumption, and potential for low loss and cost. Ferroelectrics allow
for the tuning of microwave devices by virtue of the nonlinear dependence of their dielectric permittivity on an applied
electric field. Experiments on the field-polarization dependence of ferroelectric thin films show variation in dielectric
permittivity of up to 50%. This is in contrast to the conventional dielectric materials used in electrical devices which
have a relatively constant permittivity, indicative of the linear field-polarization curve. Ferroelectrics, with their variable
dielectric constant introduce greater flexibility in correction and control of beam shapes and beam direction of antenna
structures. The motivation behind this research is applying ferroelectrics to mechanical load bearing antenna structures,
but in order to develop such structures, we need to understand not just the field-permittivity dependence, but also the
coupled electro-thermo-mechanical behavior of ferroelectrics. In this paper, two models are discussed: a nonlinear
phenomenological model relating the applied fields, strains and temperature to the dielectric permittivity based on the
Devonshire thermodynamic framework, and a phenomenological model relating applied fields and temperature to the
dielectric loss tangent. The models attempt to integrate the observed field-permittivity, strain-permittivity and
temperature-permittivity behavior into one single unified model and extend the resulting model to better fit experimental
data. Promising matches with experimental data are obtained. These relations, coupled with the expression for operating
frequency vs. the permittivity are then used to understand the bias field vs. frequency behavior of the antenna. Finally,
the effect of the macroscopic variables on the antenna radiation efficiency is discussed.
The plug-in hybrid-electric vehicle (PHEV) concept allows for a moderate driving range in electric mode but uses an
onboard range extender to capitalize on the high energy density of fuels using a combustion-based generator, typically
using an internal combustion engine. An alternative being developed here is a combustion-based thermoelectric
generator in order to develop systems technologies which capitalize on the high power density and inherent benefits of
solid-state thermoelectric power generation. This thermoelectric power unit may find application in many military,
industrial, and consumer applications including range extension for PHEVs. In this research, a baseline prototype was
constructed using a novel multi-fuel atomizer with diesel fuel, a conventional thermoelectric heat exchange
configuration, and a commercially available bismuth telluride module (maximum 225°C). This prototype successfully
demonstrated the viability of diesel fuel for thermoelectric power generation, provided a baseline performance for
evaluating future improvements, provided the mechanism to develop simulation and analysis tools and methods, and
highlighted areas requiring development. The improvements in heat transfer efficiency using catalytic combustion were
evaluated, the system was redesigned to operate at temperatures around 500 °C, and the performance of advanced high
temperature thermoelectric modules was examined.
Magnetorheological (MR) fluids have rheological properties, such as the viscosity and yield stress that can be altered by
an external magnetic field. The design of novel devices utilizing the MR fluid behavior in multi-degree of freedom
applications require three dimensional models characterizing the coupling of magnetic behavior to mechanical behavior
in MR fluids. A 3-D MR fluid model based on multiscale kinetic theory is presented. The kinetic theory-based model
relates macroscale MR fluid behavior to a first-principle description of magnetomechanical coupling at the microscale. A
constitutive relation is also proposed that accounts for the various forces transmitted through the fluid. This model
accounts for the viscous drag on the spherical particles as well as Brownian forces. Interparticle forces due to
magnetization and external magnetic forces applied to ferrous particles are considered. The tunable rheological
properties of the MR fluids are studied using a MR rheological instrument. High and low viscosity carrier fluids along
with small and large carbonyl iron particles are used to make and study the behavior of four different MR fluids.
Experiments measuring steady, and dynamic oscillatory shear response under a range of magnetic field strengths are
performed. The rheological properties of the MR fluid samples are investigated and compared to the proposed kinetic
theory-based model. The storage (G') and loss (G") moduli of the MR fluids are studied as well.
The overall goal of the research conducted in this paper is to develop next generation force feedback systems by
combining novel Magnetorheological (MR) fluid based systems with microstructural analysis and advanced control
system design. A novel 5-DOF MR fluid-based robotic arm is designed and prototyped. The 5-DOF system is used to
control a remote 5-DOF robot (the slave). Force feedback control is employed to replicate in the master those forces
encountered in the slave.
Despite vast technological improvements, the traditional internal combustion powered vehicle still achieves only 25-
30% efficiency, with the remainder lost primarily as heat. While the load leveling offered by hybrid-electric vehicle
technology helps to improve this overall efficiency, part of the efficiency gains are achieved by making new systems
such as regenerative braking viable. In a similar fashion, thermoelectric (TE) energy recovery has long been considered
for traditional vehicles with mixed results, but little has been done to consider thermoelectrics in the framework of the
unique energy systems of hybrid vehicles. Systems that may not have been viable or even possible with traditional
vehicles may offer improvements to system efficiency as well as emissions, vehicle durability, passenger comfort, and
cost. This research describes a simulation developed for evaluating and optimizing thermoelectric energy recovery
systems and results for four different system configurations. Two novel system configurations are presented which offer
the potential for additional benefits such as emissions reduction that will soon be quantified. In addition, a test setup is
presented which was constructed for the testing and validation of various thermoelectric recovery systems. Actual test
performance was near the expected theoretical performance and supported the conclusions reached from the computer
High customization costs and reduction of natural mobility put current rehabilitative knee braces at a disadvantage. A
resolution to this problem is to integrate a Magnetorheological (MR) fluid-based joint into the system. A MR joint will
allow patients to apply and control a resistive torque to knee flexion and extension. The resistance torque can also be
continuously adjusted as a function of extension angle and patient strength (or as a function of time), which is currently
impossible with state of the art rehabilitative knee braces. A novel MR fluid-based controllable knee brace is designed
and prototyped in this research. The device exhibits large resistive torque in the on-state and low resistance in the offstate.
The controllable variable stiffness, compactness, and portability of the system make it a proper alternative to
current rehabilitative knee braces.
Ferromagnetic Shape Memory Alloys (FSMAs) in the nickel manganese gallium system have been shown to exhibit large magnetically induced strains of up to 9.5% due to magnetically driven twin variant reorientation. In order for this strain to be reversible, however, an external restoring stress or magnetic field needs to be applied orthogonal to the field and hence the implementation of Ni-Mn-Ga in applications involves the use of electromagnets, which tend to be heavy, bulky and narrowband. In previous work at The Ohio State University a sample of Ni50Mn28.7Ga21.3 has been shown to exhibit reversible compressive strains of -4200 microstrain along its  direction when a magnetic field is applied along this same direction and no externally applied restoring force is present. This reversible strain is possible because of an internal stress field associated with pinning sites induced during manufacture of the crystal. This paper analyzes the switching between two variant orientations in the presence of magnetic fields (Zeeman energy) and pinning sites (pinning energy) through the formulation of a Gibbs energy functional for the crystal lattice. Minimization of the Gibbs free energy yields a strain kernel which represents the predicted behavior of an idealized 2-dimensional homogeneous single crystal with a single twin boundary and pinning site. While adequate, the kernel has limitations because it does not account for the following: (a) Ni-Mn-Ga consists of a large number of twin variants and boundaries, (b) the strength of the pinning sites may vary, and (c) the local and applied magnetic field will differ due to neighbor-to-neighbor interactions. These limiting factors are addressed in this paper by considering stochastic homogenization. Stochastic distributions are used on the interaction field and on the pinning site strength, yielding a phenomenological model for the bulk strain behavior of Ni50Mn28.7Ga21.3. The model quantifies both the hysteresis and saturation of the strain. Constrained optimization is used to determine the necessary parameters and an error analysis is performed to assess the accuracy of the model for various loading conditions.
The disadvantage of current knee braces ranges from high cost for customization to a loss in physical mobility and limited rehabilitative value. One approach to solving this problem is to use a Magnetorheological (MR) device to make the knee brace have a controllable resistance. Our design solution is to replace the manufacturer's joint with an rotary MR fluid based shear damper. The device is designed based on a maximum yield stress, a corresponding magnetic field, a torque and the MR fluid viscosity. The analytical and experimental results show the advantages and the feasibility of using the proposed MR based controllable knee braces.
The idea of this paper is to design a Magnetorheological (MR) fluid based damper for steer-by-wire systems to provide sensory feedback to the driver. The advantages of using MR fluids in haptic devices stem from the increase in transparency gained from the lightweight semiactive system and controller implementation. The performance of MR fluid based steer-by wire system depends on MR fluid model and specifications, MR damper geometry, and the control algorithm. All of these factors are addressed in this study. The experimental results show the improvements in steer-by-wire by adding force feedback to the system.
Active shape and vibration control of large structures have long been desired for many practical applications. PVDF
being one of the most suitable materials for these applications due to its strong piezoelectric properties and availability in
thin sheets has been the focal point of most researchers in this area. Most of the research has been done to find an open
loop solution, which would be able to shape the structure as per the desired requirements in an ideal atmosphere.
Unmodeled dynamics and external disturbances prevent the open loop (no feedback) solution from achieving the desired
shape. This research develops a dynamic model of a laminated plate consisting of two layers of PVDF film joined with a
layer of epoxy. The orthotropic properties of PVDF have been modeled and the epoxy layer is considered to be isotropic.
A general control model is developed, which would work for most boundary conditions and developed for a simply
supported beam with patch actuators. The methodology is then extended for a simply supported laminated plate. This
model could be used for real time dynamic disturbance rejection and shape and vibration control of the structure.
A vibration confinement is the act of restricting the vibration of a structure to a certain region on the structure. Confinement or restriction of vibrations to relatively unimportant areas helps in isolating vibration-sensitive components from vibratory disturbances and mitigating the damage of the components. In this research, an active vibration confinement technique based on full state feedback strategy, which was proposed by previous authors, is experimentally implemented and verified. The algorithm constructs a square matrix of the closed-loop eigenvectors and a rectangular matrix of the corresponding control vectors. Then, the control gain is uniquely determined by right-multiplying the inverse of the eigenvector matrix to the control vector matrix. The experiment is conducted for a pinned-pinned aluminum beam with two piezoelectric film sensors and two piezoceramic actuators bonded symmetrically along the beam. The vibration of the beam is estimated using an observer and the control actuation is realized using two piezoceramic patch actuators. Experimental results show that active vibration confinement can actually be realized for a lightly damped system with piezoceramic patch actuators.
The shape control of thin, flexible structures has been studied primarily for edge-supported thin plates. For applications involving reconfigurable apertures such as membrane optics and active RF surfaces, corner-supported configurations may prove more applicable. Corner-supported adaptive structures allow for parabolic geometries, greater flexibility, and larger achievable deflections when compared to edge-supported geometries under similar actuation conditions. Preliminary models have been developed for corner-supported thin plates actuated by isotropic piezoelectric actuators. However, typical piezoelectric materials are known to be orthotropic. This paper extends a previously-developed isotropic model for a corner-supported, thin, rectangular bimorph to a more general orthotropic model for a bimorph actuated by a two-dimensional array of segmented PVDF laminates. First, a model determining the deflected shape of an orthotropic laminate for a given distribution of voltages over the actuator array is derived. Second, symmetric actuation of a bimorph consisting of orthotropic material is simulated using orthogonally-oriented laminae. Finally, the results of the model are shown to agree well with layered-shell finite element simulations for simple and complex voltage distributions.
In this study the authors develop haptic systems for telerobotic surgery. In order to model the full range of tactile force exhibited from an MR damper a microstructural, kinetic theory-based model of Magnetorheological (MR) fluids has been developed. Microscale constitutive equations relating flow, stress, and particle orientation are produced. The model developed is fully vectorial and relationships between the stress tensor and the applied magnetic field vector are fully exploited. The higher accuracy of the model in this regard gives better force representations of highly compliant objects. This model is then applied in force feedback control of single degree of freedom (SDOF) and two degrees of freedom (2DOF) systems. Carbonyl iron powders with different particle sizes mixed with silicone oils with different viscosities are used to make several sample MR fluids. These MR fluid samples are then used in three different designed MR dampers. A State feedback control algorithm is employed to control a SDOF system and tracking a 2-D profile path using a special innovative MR force feedback joystick. The results indicate that the MR based force feedback dampers can be used as effective haptic devices. The systems designed and constructed in this paper can be extended to a three degree of freedom force feedback system appropriate for telerobotic surgery.
Our previous work on ferromagnetic shape memory Ni50Mn28.7Ga21.3 demonstrates reversible compressive strains of -4100 microstrain along the  direction under the application of a magnetic field also along the  direction with no external orthogonal restoring force. The reversibility of the strains is due to internal bias stresses oriented orthogonal to the field. These results show promise for the use of Ni-Mn-Ga as the core material in solenoid transducers. In this paper, the reversible strains are explained by considering pinning sites as the source of the internal bias stresses in the material. Following prior work by Kiefer and Lagoudas, a phenomenological model is constructed for the motion of twin variants in the presence of an orthogonal pair formed by a magnetic field and an internal bias stress. The model is formulated by considering the Zeeman, elastic, and pinning energies, from which an appropriate Gibbs energy function is constructed. Minimization of the Gibbs function then yields a constitutive model for the strain. The accuracy of this model is studied and its implementation as a hysteresis kernel in homogenization theories is discussed.
High bandwidth actuation systems that are capable of simultaneously producing relatively large forces and displacements are required for use in automobiles and other industrial applications. Conventional hydraulic actuation mechanisms used in automotive brakes and clutches are complex, inefficient and have poor control robustness. These lead to reduced fuel economy, controllability issues and other disadvantages. This paper involves the design, development, testing and control of a two-stage hybrid actuation mechanism by combining classical actuators like DC motors and advanced smart material actuators like piezoelectric actuators. The paper also discusses the development of a robust control methodology using the Internal Model Control (IMC) principle and emphasizes the robustness property of this control methodology by comparing and studying simulation and experimental results.
In this paper, concepts associated with the Preisach model and nonlinear mapping functions (neural networks) are coupled to model the hysteretic behavior of piezoceramic actuators. Preisach concepts are utilized in choosing the initial data points and calculating the final displacements having nonlocal memory. In a traditional Preisach model generalization is typically handled by interpolation functions. These functions can lead to significant errors unless the number of data points is considerably high. In this study the generalization of all first order reversal curves is provided by a single neural network. The goal of this work was to enable real-time implementation and learning with a "limited" number of variables. Finally, a novel on-line training approach was developed to account for errors caused by frequency dependency and large variations of the input of the actuator. Results show excellent agreement between simulated and experimental results.
Ferromagnetic shape memory nickel-manganese-gallium (Ni-Mn-Ga) has shown tremendous promise as an actuator material due to its large strain and high bandwidth. However, current Ni-Mn-Ga devices are electromagnet based as this configuration allows for an externally applied force perpendicular to the applied field, and are therefore bulky, energy inefficient, and narrowband. We investigate the dynamic response of Ni-Mn-Ga driven by a solenoid transducer in which the magnetic field is aligned collinearly with the loading stress. The work focusses on the quasistatic and dynamic testing of a Ni50Mn28.7Ga21.3 sample which is believed to have an internal stress field which plays the role of the restoring force necessary for reversible strains. This sample is shown to exhibit reversible compressive strains of -0.41% with no external forces applied. Several experimental apparatus are used in order to verify these results. The measurements demonstrate a 231% change in stiffness with applied dc magnetic fields.
In this research a broadband passive vibration control technique using a semi-active circuit is presented. A digitally tunable RL shunt circuit and a semi-active mode identifier are developed using 8-bit CMOS microcontrollers to control multiple vibratory modes in a mechanical system. In order to increase the adaptability of the controller, the effects of additional capacitors in the circuit are investigated. The governing equations for the coupled electro-mechanical system are introduced using Hamilton’s Principle and finite element analysis. The system is verified experimentally using and the simulation and experimental results are provided in multiple formats.
The research in this study develops an analysis technique for mechanized solid-state actuators. The methodology's strength stems from the fact that it can be applied to a single solid-state actuator or an actuator that is coupled to a compliant mechanism (mechanized). The technique couples the actuator to any compliant mechanism and it takes into account interactions between the mechanized actuator and its load. Thus the methodology can be applied to a myriad of loaded systems. The analysis technique is rooted in thermodynamics and thus can be expanded to a wide range of systems (piezoelectric, electrohydraulic, electrostrictive, magnetostrictive, etc.). The methodology uses energy transfer as a medium to develop analytical relationships between input parameters and output parameters. Results of the technique are consistent with existing energy-based techniques and experimental data.
Ferromagnetic shape memory martensites in the Ni-Mn-Ga system have been demonstrated to achieve a number of the criteria required for next generation actuators including the production of large theoretical strains up to 6%. The large strain originates in the rotation of twin variants and associated twin boundary motion which occurs in response to magnetic fields. The magnetic activation holds promise in actuator design because it can lead to higher bandwidths than those achieved through pure martensite-austenite phase transformation, as is the case with thermally-activated shape memory alloys. In this paper, we report on experimental measurements collected from a cylindrical Ni49.0Mn30.0Ga21.0sample alloy, driven as cast by a collinear magnetic field-stress pair. Despite the lack of a known restoring force and the fact that no "training" procedures are applied, quasi-static strains as large as 4300 micro-strain are shown. Furthermore, dynamic results in the DC-20kHz range are presented which would suggest the presence of a Delta-E effect similar to that seen in Terfenol-D but exhibiting an opposite dependence of stiffness with DC field. The potential implications of the results for the design and control of dynamic structures based on Ni-Mn-Ga are very significant.
The work in this study develops a methodology for using Polyvinylidene Fluoride (PVDF) film for gathering impact information from a structure. The method can be employed on sensors that are deployed over rigid structures or those that are placed on top of compliant/viscoelastic structures. This method utilizes spatially shaded (etched) electrodes, which allow for selective charge collection and signal processing. This means that impact information, such as impact location and impact angle, can be directly related to the time varying measured output voltage. The basic equations describing charge collection are developed followed by the development of an experimental technique that can be used for charge collection. Results were validated on an experimental test stand and show acceptable performance with error ranging between 0.025 cm (0.01 in) and 0.635 cm (0.25 in).
Piezoceramic actuation has become an area of increased interest in the past ten years. Having been used for many years as sensors in such applications as pressure transducers and smoke detectors, piezoceramics are now being used as prime movers in fuel injectors and valve lifters. In an effort to aid the engineering community, this paper will conduct a comprehensive review of several piezoceramic actuators. Classical design parameters will be derived for each actuator such as blocked force and free stroke. In addition, more esoteric entities such as mechanical efficiency and energy density will also be derived. The result will be design metrics of popular piezoceramic actuators containing vital design equations, validated with empirical data. Of the many different configurations of piezoceramic actuators, this paper will investigate the bimorph and unimorph bender. These actuator types are finding increased use in semi-active structural damping, energy harvesting and vibration control. The work in this paper will show experimental verification of various actuator types as well as theoretical derivations. In addition to unimorphs, bimorphs and stack actuators a novel type of unimorph bender, the THUNDER actuator (developed and licensed by NASA) will be included in the review.
The work in this study develops the framework for placement and actuation of novel mechanically reconfigurable dual-offset contour beam reflector antennas (DCBRA). Towards that end the methodology for the antennas' design is defined. The antenna designed in this study employs piezoelectrically driven ball screw actuators. These actuators are attached to a flexible sub reflector surface and are used to vary radiation pattern. In addition, two separate optimization problems are stated and solved: Actuator position optimization and actuation value optimization. For the former, a method termed as Greatest Error Suppression method is proposed where the position of each actuator is decided one by one after each evaluation of the error between the desired subreflector shape and the actual subreflector shape. For the second problem, a mathematical analysis shows that there exists only one optimal configuration. Two optimization techniques are used for the second problem: the Simulated Annealing algorithm and a simple univariate optimization technique. The univariate technique always generates the same optimal configuration for different initial configurations and it gives the low bound in the evaluation of the error. The Simulated Annealing algorithm is a stochastic technique used to search for global optimum point. Finally, as an example, the results of the proposed optimization techniques are presented for the generation of a subreflector shape for the geographical outline of Brazil.
Force feedback is a new technology that has great potential in human-machine interfaces. While guiding the end effector of a robot through an environment using a hand-held actuator, force feedback is needed to make the user feel the environment conditions like stiffness along which the end effector moves. This along with the already available visual feedback will allow the user to guide the robot exactly along the path that he or she intends thereby enhancing the performance. Easily controllable actuators that give quick response at the user end are needed here. This paper demonstrates the effectiveness of MR fluid devices in such force feedback applications. The force-feedback experiment includes a simple setup that depicts a typical situation wherein a user controls the movement of an external linear hydraulic actuator using a MR sponge damper. Force and displacement sensors sense the environment conditions along which the end effector of the hydraulic actuator moves. This information is then used to control the MR damper to provide appropriate force feedback to the user. The setup is tested with different environments like springs with various stiffnesses and for extreme cases with mechanical stops thereby demonstrating the flexibility in using MR sponge dampers for various force feedback applications.
This paper introduces a model for a vibration control system in which spatially etched Polyvinylidene Fluoride (PVDF) was utilized to implement uniform damping control on a distributed system. Uniform damping node control (UDNC) theory states that near optimal vibration control can be achieved when the following criteria are met: all modes are damped at the same exponential decay rate, the open loop and closed loop natural frequencies of the structure are identical, and the closed loop modal shapes are identical to the open loop modal shapes. To help accomplish this, in a system with N modes participating in a response, sensor/actuator pairs are placed at the nodes of the N+1 mode. Spatially shaded PVDF actuators are distributed actuators that produce pseudo discrete forces due to the special weighting applied to the etched electrodes. The system was implemented using a spring steel cantilevered beam and spatially etched PVDF actuators which were placed according to nodal control theory (NCT). When given the set of gains that are attributed to UDNC, the modes de-couple, reducing spillover. This experiment marks the first time that distributed control techniques such as uniform damping control were realized in a discrete fashion by utilizing spatially shaded piezoelectric actuators.
In this research, a broadband variable passive and semi- active circuit is presented. The detailed procedure to obtain the augmented second order differential equations of motion for an electrical dynamic absorber (shunted circuit) using integrated piezoelectric material are given using Hamilton's principle and the finite element modeling procedure. The effect of the electrical dynamic absorber is shown through frequency response and analysis by varying the capacitance and inductance in the shunted circuit. Modal identification and gain scheduling techniques are also employed to identify each mode of the vibration of the structure. Simulations are implemented using a cantilevered aluminum beam with a PZT-5H (lead zirconate titanate) patch. The simulated results are provided in multiple formats.
Consistent changes in both commercial and military satellite needs have created the need for antennas with additional flexibility. Military surveillance may require the ability to focus the radiation pattern to increase the bandwidth or resolution in a certain area. Commercial satellites may need to change coverage area to meet evolving consumer needs or to compensate for adverse weather or atmospheric conditions. Recent studies on active antennas have shown that the far field radiation pattern can be changed by altering the shape of the sub reflector. In this research, we control the antenna far field radiation pattern by controlling the shape of the sub reflector using numerous point actuators placed perpendicular to the reflector surface. The PZT stack coupled with a stick-slip mechanism give the point actuators used in this design an advantage over similar studies using PZT bimorph or PVDF actuators to generate the actuation force in that the displacement can be maintained without the continuous application of voltage. An electromechanical model is used to describe the motion of the stack, and the stick slip mechanism is modeled similar to power screw-type actuators. A combined finite element/electromagnetic analysis code is used to determine the desired shape of the reflector, and the corresponding actuator displacements. The final shape of the reflector is verified using stereo photogrammetry.
Sliding mode control has become one of the most powerful control methods for variable structure systems, a set of continuous systems with an appropriate switching logic. Its robustness properties and order reduction capability have made sliding mode control one of the most efficient tools for relatively higher order nonlinear plants operating under uncertain conditions. Piezo-electric materials possess the property of creating a charge when subjected to a mechanical strain, and of generating a strain when subjected to an electric field. Piezo-electric actuators are known to have a hysteresis due to the thermal motion and Coulomb interaction of Weiss domains. Because of the thermal effect the hysteresis of piezo-electric actuators is reproducible only with some uncertainty in experiments. The robustness of sliding mode control under uncertain conditions has an advantage in handling the hysteresis of piezo-electric actuators. In this research sliding mode control is used to control the shape of one- and two-dimensionally curved adaptive reflectors with piezo-electric actuators. Four discrete linear actuators for the one-dimensionally curved reflector and eight actuators for the two-dimensionally curved reflector are assumed.
In this paper, the authors present vibration mode identification of rectangular plates by using discrete piezoelectric materials. The novelty in this study stems from the fact that only spatial information is used. The analytical development and numerical simulation results of the method are also included. For the structural vibration control community, identification of the dominant vibration has been an important issue. If the dominant vibration modes are successfully identified, the control engineers can choose a proper control gain set which has been pre-tuned for the identified vibration mode. As the development of piezoelectric materials progressed, vibration mode identification techniques step into a new stage. Several papers reported vibration mode identification by using distributed piezoelectric modal sensors. Unfortunately, the spatially filtering methods need specially designed configuration corresponding to the geometry of the structures. These difficulties hinder the application and development of modal sensing and vibration control technology. In this paper, the authors develop a new method of the mode identification, and present analytical simulations for rectangular plates and circular plates. Finally, experimental verification of the method is also presented.
A novel way to design, synthesize and adjust the reconfigurable dual offset contour beam reflector antenna employing an adjustable subreflector is presented. The work also presents a graphical user interface based computer code that connects the electro-magnetic effects to the mechanical surface deflections. The subreflector surface is described by using the finite element method and the far-field radiation pattern is calculated by reflector diffraction synthesis. The reflector surface shape is adjusted using a set of linear piezoelectric point actuators attached to its back surface, from which the diffraction synthesis code calculates the radiation pattern. An example of this method applied to the contiguous US is also presented. As a future work, a software package will be built where the finite element code and the diffraction synthesis code are combined, and it will be used for advanced actuator placement and reflector design problem.
In this research, a real-time simulation of full state- derivative feedback control using acceleration measurements is presented. A new optimal control design algorithm based on non-standard performance indices in the 'Reciprocal State Space' framework is employed to design controllers and observers. A piezoelectric material (PZT) laminated cantilevered steel beam with an accelerometer is selected as a test bed. The system is modeled utilizing a multi-layered integrated finite element method with four degree of freedom, one-dimensional, bending elements. The resulting model, presented in generalized coordinates, is transformed to real orthogonal modal coordinates and a reduced order model is developed. Simulated results are provided in multiple formats.
Recently, singly curved smart antennas that have the ability of changing their reflector shape through the use of piezoelectric actuators have been studied. The results show that those antennas have the ability to steer and shape radiation patterns in the far-field. As an extension of the previous work, this study examines the use of `doubly curved'--spherical--antenna structures to achieve better performance in controlling an antenna's coverage area. The spherical antenna is made of a thin plastic shell with a small hole at the apex for base mounting. As actuators, four PZT strip patches are attached along the meridians separated by 90 degrees respectively. The antenna structure is modeled following Reissner's shallow spherical shell theory, and the forces developed by the PZT actuators are applied as the boundary conditions at the outer edge. The deformed shape of the antenna is calculated with respect to the applied voltage and the far-field radiation pattern for the shape is simulated on the computer. Based on the theoretical work, an actual working model of the doubly curved antenna is built. Several experiments with the model verify that the beam steering and beam shaping mode can be achieved in the real situation.
Recently the design of curved thunder actuators (deflections from 1 mm - 15 mm) has been a topic of study for many researchers. The work in this study deals with the development of a general technique based on shell theory. The technique can be applied to a broad array of actuators to include: Rainbows, Thunders, C-Blocks and others. The formulation begins with the equations for a general shell theory. Next the equations are reduced to the forms of equations for the particular actuators in a manner that they can be applied to a myriad of curved composite actuators. The technique is then experimentally verified on a Thunder actuator system. Next, the system is controlled using both classical and intelligent control techniques. In addition hardware and circuitry issues are explored.
The use of smart materials (piezoceramic elements) in structure vibration damping has risen in popularity. The ability to use these materials as both sensors, capturing a voltage upon straining of the material, and actuators, acquiring a displacement due to an electric voltage, has increased. The work presented in this paper develops the use of robust intelligent control as applied to smart materials. A steel cantilever beam was constructed as the experimental (physical) plant. Piezoceramic material, lead zirconate titanate, was surface mounted as both sensors and actuators. The controller was formed using algorithms produced from adaptive fuzzy controls. Fuzzy model reference learning control (FMRLC) is a learning system with the capability to improve its performance over a period of time when various plant uncertainties are introduced. The expected goal of this paper is to dampen the fundamental vibration mode of the beam utilizing the intelligent control algorithm developed. Other controllers, such as positive position feedback (PPF) and direct fuzzy (DF), were developed and compared to the adaptive fuzzy controller. The robustness of the system was also examined when the cantilever beam system properties changed. Extra masses were added to account for the variations of the system parameters. The FMRLC controller showed a dramatic improvement over the PPF and DF. It is the adaptive nature of the FMRLC that makes the system robust to parameter changes.
The major drawback of a microstrip patch antenna is it's narrow bandwidth characteristics. One method that has been investigated to increase bandwidth is the addition of a parasitic element to the microstrip patch antenna. In an active microstrip patch antenna, variable bandwidth can be achieved by varying the spacing between the antenna and the parasitic element, which is fixed to a dielectric plate. In this study, an actuator is developed, tested and employed on an actual microstrip patch antenna and it's parasite. Since a relatively large displacement (1 cm) is needed, this mesoscale actuator is comprised of stacked Rainbow actuators. This study takes advantage of the fact that, for antennas operating at higher frequencies, smaller absolute displacements will result in significant percentage changes in antenna bandwidth. The use of the parasite and the active system accounted for up to a factor of five increase in antenna bandwidth. Various control techniques were employed to counteract the effects of hysteresis and creep on the actuator. Because the use of metal components can degrade antenna performance, emphasis was placed on synergy in the design process.
Recently, it has been demonstrated that aperture antennas can have their performance improved by utilizing PVDF as a shape controlling actuator. Since PVDF is a polymer with limited control authority, these antennas can only be employed in space based applications. This study examines more robust antenna structures devised of a thick metalized substrate with surface bonded piezoceramic (PZT) actuators. In this work, PZT-actuated adaptive antennas of cylindrical- cut shape are studied. First, the PZT-actuated antenna surface is modeled based on the classical curved beam theory and Newton's method. Second the Voltage vs. Deflection relationship is experimentally verified. Third, the resulting far field radiation pattern is simulated on computer.
Recent studies have shown that reflector surface adaptation can achieve performance characteristics on the order of some phase array antennas without the complexity and cost. The work presented in this study develops the experimental groundwork for a class of antennas capable of variable directivity (beam steering) and power density (beam shaping) The actuation for these antennas is employed by bonding polyvinylidene fluoride (PVDF) film to a metalized mylar substrate. A voltage drop across the material will cause the material to expand or contract. This movement causes a moment to be developed in the structure which causes structural bending. Several studies of flexible structures with PVDF films have shown that cylindrical antennas can achieve significant deflections and thereby offer beneficial changes to radiation patterns emanating from aperture antennas. In this study, relatively large curved actuators are modeled and a deflection vs. force relationship is developed. This relationship is then simulated and compared to experimental results. A final simulation of the far field radiation patterns from a given set of deflections is then presented.
Recent studies have shown that reflector surface adaptation can achieve performance characteristics on the order of phase array antennas without the complexity and cost. The work proposed in this study develops a class of antennas capable of variable directivity (beam steering) and power density (beam shaping). The actuation for these antennas is employed by either polyvinylidene fluoride film bonded to a metalized mylar skin or shape memory alloys embedded in a composite structure. Theoretical studies of flexible antennas have shown that cylindrical antennas can achieve a directivity variation (beam scanning) of over 10 degree(s) and an increase in ground coverage of over 40%. In this study, prototypes are modeled and simulated to verify results.