Piezoelectric patch-type actuators are being considered for use in acoustic control and vibration control of complex mechanical structures such as aircraft fuselages and automobile interiors. For complex structures, it is often difficult to predict the best location of actuator-structure interaction. Currently, piezoelectric patch-type actuators are bonded permanently to the host structure using a technique that requires surface preparation. This technique is not well suited for actuator performance testing and model verification since attaching the actuator is time-consuming, removing the actuator is difficult, and the actuator is destroyed when it is removed. We present three alternate techniques for bonding flat piezoelectric patch-type actuators to structures. These techniques allow the actuator to be attached quickly, removed easily, and reused. The alternate techniques and a permanent bonding technique are used to attach actuators to a clamped-free beam. For each attachment technique, we obtain the frequency response functions, actuator authority levels, and damping ratios. We also obtain the degradation of the actuator authority and damping ratio as the actuator is reused. For each attachment technique, we compare the measured performance to the performance predicted from a pin-force model of that actuator attachment. The attachment techniques that allowed us to make removable, reusable piezoelectric actuators were shown to provide structural actuation very similar to actuation provided by permanently attached piezoelectric actuators. A small but statistically significant change in authority occurred as a result of removing the actuator. The confidence intervals of actuator authority increased in frequency regions of antiresonance and closely spaced modes. The pin-force model did not provide an accurate analysis method for predicting actuator authority. / Master of Science

The effect of the shape of piezoceramic actuators on the vibration response of a simply supported beam is investigated. An equation is derived to convert between the shape of the piezoceramic actuator and the resulting moment distribution caused on the structure. A beam simulation program is then created to model the vibrations caused by various shaped moment distributions exciting a simply supported beam. The length of the moment distribution is iterated from the length of the beam to zero length, within the program, to show the trends in modal amplitudes. The amplitude of each mode is then plotted for each length of the moment distribution. An equation is then derived to explain the resulting minimums and maximums of the modal amplitudes. The equation is shown to be a useful tool in designing shapes to meet specific control criteria. An example is given showing how the shape of the actuator can be designed to give superior performance for specific control criteria than a traditional rectangular shape. Two possible actuator shapes are shown for the situation. One shape is optimized for the given control criteria by causing the maximum response for the critical mode. The results from the beam simulation for both shapes are shown. The shape of the actuator may now be used as a variable in the cost function for control optimization. / Master of Science

The design and analysis of finite length, multiple layered, induced strain actuators is investigated. A model of an arbitrary multiple layered actuator is utilized to predict the applied force and moment from the i^th layer onto a structure. The transverse equations of motion of a simply supported beam are derived using Timoshenko beam theory. This approach accounts for shear deformation and allows the actuator-applied moments to be directly incorporated into the equations of motion without further approximation. The model is cast in state space form and an assumed mode method is used to solve for the forced response of a nonuniform beam. Experiments are performed verifying the developed analytical model. The first experiment characterizes the dynamic properties of five different actuator/substructure configurations. Results indicate the system natural frequencies decreased and the structural damping increased with more attached actuators. Analytical predictions are shown to be in good agreement with the experimental results. / Master of Science

Active control of sound transmission through an elastic plate placed between two reverberation chambers is studied experimentally. Active acoustic control is performed using piezoelectric sensors and actuators bonded to the plate. The control technique uses an adaptive control algorithm. Results are presented for harmonic excitation provided by a speaker in the source chamber at two resonant frequencies of the plate. Influence of different types of error sensors, varied actuator locations, and varied speaker locations are studied. Compared to microphone sensors in the receiving chamber, piezoelectric sensors are shown to be effective in reducing sound transmission through the plate. Average reduction of sound pressure level (SPL) on the order of 20 dB or 13 dB are achieved when the plate vibrates at mode (3,1) or (3,3). Microphone sensor locations are shown to influence the controlled sound field, those located where the direct sound field is dominant result in larger SPL reductions. SPL reductions are caused by two mechanisms: modal reduction and modal restructuring, and the dominance of either is shown to depend on actuator locations. When the sound field is non-diffuse, speaker locations influence the SPL and the SPL reduction by changing the plate's structural response. Also included in this work, previously developed one-dimensional (I-D) modal sensor theory for beams is used to develop modal sensors for a clamped plate. Two I-D modal sensors are applied to a fully clamped plate and each shown to observe a particular subset of plate vibration modes. Previous work developed the theory for two-dimensional (2-D) modal sensors for simply-supported plates. A necessary and sufficient condition for the spatial functions of 2-D modal sensors are developed for plates with arbitrary boundary conditions. / Master of Science

Of primary importance to the design and application of adaptive structures is a modeling method to allow for performance prediction and parametric optimization of the integrated system. The statics-based modeling approaches have been applied to model piezoelectric (PZT) actuator-driven adaptive structures. The dynamic interaction between the actuators and their host structures has been ignored, and the system energy conversion can’t be predicted. As a matter of fact, PZT actuator-driven smart structures are complex electromechanical coupling systems in which electrical energy is converted into mechanical energy and vice-versa. The actuator outputs and the system energy conversion are dominated by the complex electro-mechanical impedance of the system. The entire actuator/substrate system can thus be essentially represented by a coupled impedance-based system model. This research presents such an impedance-based electro-dynamics analytical method and the experimental investigation for integrated PZT/substrate systems. When compared with the conventional static models, the system modeling method has revealed the physical essence and the interconnections among the intelligent elements and supporting structures. The frequency-dependent behaviors of the actuator and the dynamic response of the integrated system are accurately predicted. The theoretical model was developed for generic PZT actuator-driven active structures. The actuation force was evaluated as a result of the dynamic interaction between the actuator and the host structure. The model was then extended to include the electrical parameters of the PZT actuator such that the power flow and consumption of the integrated system can be predicted. The system dissipative power was then treated as the equivalent generation source to evaluate a temperature rise and thermal damage of the actuator. To examine the utility and generality of the system modeling method, the developed model was applied to typical two-dimensional structures such as thin plates and thin shells, and to one-dimensional structures such as the circular rings and beams. The design-related mechanical and thermal stress characteristics of the actuators were also specifically investigated. In addition to the theoretical work, experiments were conducted. The PZT actuator-driven simply-supported plate was built and tested. The velocity response of the integrated plate and the dynamic strain of the PZT actuators were measured. The coupled electromechanical admittance of the real system was also directly measured using an impedance analyzer. The predicted solutions agree with the experimental results in all of the tested cases, verifying the theoretical model. / Ph. D.

Thesis (M. Tech.) -- Central University of Technology, Free State, 2009

This thesis presents mathematical modeling and control techniques that can be used to predict and specify performance of biologically inspired actuation systems called cellular actuators. Cellular actuators are modular units designed to be connected in bundles in manner similar to human muscle fibers. They are characterized by inherent compliance and large numbers of on-off discrete control inputs. In this thesis, mathematical tools are developed that connect the performance to the physical manifestation of the device. A camera positioner inspired by the human eye is designed to demonstrate how these tools can be used to create an actuator with a useful force-displacement characteristic. Finally, control architectures are presented that use discrete switching inputs to produce smooth motion of these systems despite an innate tendency toward oscillation. These are demonstrated in simulation and experiment.

The ability to reduce flexural vibrations of lightweight structures has been a goal for many researchers. A type of transducer-controller system that accomplishes this is a piezoelectric patch connected to an electrical impedance, or shunt. The piezoelectric patch converts the vibrational strain energy of the structure to which it is bonded into electrical energy. This converted electrical energy is then modified by the shunt to influence to mechanical response. There are many types of shunt circuits which have demonstrated effective control of flexural systems. Of interest in this work is the negative capacitance shunt, which has been shown to produce significant reduction in vibration over a broad frequency range. A negative capacitance circuit produces a current that is 180̊ out of phase from a traditional, passive capacitor. In other words, the voltage of the capacitor decreases as charge is added. The negative capacitance shunt consists of a resistor and an active negative capacitance element. By adding a resistor and negative capacitor to the electrical domain, the shunt acts as a damper and negative spring in the mechanical domain. The performance of the negative capacitance shunt can be increased through proper selection of the shunt's electrical components. Three aspects of component selection are investigated: shunt efficiency, maximum suppression, and stability. First, through electrical modeling of the shunt-patch system, the components can be chosen to increase the efficiency of the shunt for a given impedance. Second, a method is developed that could be utilized to adaptively tune the magnitude of resistance and negative capacitance for maximum control at a given frequency. Third, with regard to stability, as the control gain of the circuit is increased, by adjusting the circuit parameters, there is a point when the shunt will become unstable. A method to predict the stability of the shunt is developed to aid in suppression prediction. The negative capacitance shunt is also combined with a periodic piezoelectric patch array to modify the propagating wave behavior of a vibrating structure. A finite element method is utilized to create models to predict both the propagation constant, which characterizes the reduction in propagating waves, and the velocity frequency response of a full system. Analytical predictions are verified with experimental results for both a 1- and 2-D periodic array. Results show significant attenuation can be achieved with a negative capacitance shunt applied to a piezoelectric patch array. Three electromechanical aspects are developed: design for maximum suppression, more accurate stability prediction, and increased power-output efficiency. First, a method is developed that may be used to adaptively tune the magnitude of resistance and negative capacitance for maximum suppression. Second, with regard to stability, a method is developed to predict the circuit components at which the circuit will obtain a stable output. Third, through electrical modeling of the shunt-patch system, the components are chosen to increase the power output efficiency of the shunt circuit for a given impedance. The negative capacitance shunt is also combined with a periodic piezoelectric patch array to modify the propagating wave behavior of a vibrating structure. Analytical predictions are verified with experimental results for both a 1- and 2-D periodic array. Results show significant attenuation can be achieved with a negative capacitance shunt applied to a piezoelectric patch array.

Pb(Zr₀.₅₂Ti₀.₄₈)O₃ (PZT) thin films are of interest for their large dielectric permittivity, ferroelectric, and piezoelectric properties. The material has been widely studied for use in high frequency transducers, multi-layered capacitors, and ferroelectric random access memory. Copper foils are an inexpensive, flexible substrate with a low resistivity which makes them ideal for many transducer and capacitor applications. PZT thin films on copper foils were produced by RF sputtering and crystallized under reducing conditions. Causes and prevention of a cuprous oxide interlayer are discussed. The film structure was characterized by XRD, SEM, and AFM. The permittivity was low, but remanent polarization increased to as high as ~40 μC/cm² as film thickness and crystallization temperature increased. Residual stresses were measured by x-ray diffraction using the sin²ψ method. The relative permittivity of the PZT/Cu films was measured as a function of applied AC electric field. By performing a Rayleigh analysis on this data one can determine the relative contributions of the intrinsic, reversible, and irreversible components to the permittivity. The residual stress could be correlated to the reversible part of the permittivity. The first order reversal curves (FORCs), which characterize the ferroelectric switching, give indications of the defect state of the film. Cantilever energy harvesters were fabricated. Large electrodes were able to be evaporated onto the films after oxidizing pinholes and cracks on a hot plate. Devices were tested on a shaker table at < 100 Hz. A dynamic model based on Euler-Bernoulli beam equations was used to predict power output of the fabricated devices. The observed output was comparable to model predictions. Resonant frequency calculations were in line with observed first and second resonances at ~17 Hz and ~35 Hz which were also close to those predicted by the dynamic model. / Graduation date: 2013

In this thesis, a systematic study has been carried out on the synthesis, characterization and device fabrication of piezoelectric ZnO nanstructures. The achieved results are composed of the following four parts. Firstly, through a systematic investigation on the Sn-catalyzed ZnO nanostructure, an improved understanding of the chemical and physical process occurring during the growth of hierarchical nanostructures has been achieved. Decomposed Sn from SnO2 has been successfully demonstrated and proved to be an effective catalyst guiding the growth of not only aligned ZnO nanowires, but also the hierarchical nanowire-nanoribbon junction arrays and nanopropeller arrays. During the vapor-liquid-solid (VLS) catalyzing growth process at high temperature, Sn in the liquid state has been proved to be able to guide the growth of nanowires and nanoribbons in terms of growth directions, side facets, and crystallographic interfaces between Sn and ZnO nanostructures. Secondly, using pure ZnO as the only source material, by precisely tuning and controlling the growth kinetics, a variety of hierarchical polar surface dominated nanostructures have been achieved, such as single crystal nanorings, nanobows, nanosprings and superlattice nanohelices. High yield synthesis of ZnO nanosprings over 50% has been successfully obtained by mainly controlling the pre-pumping level associated with the partial pressure of residual oxygen during the vapor-solid growth process. The rigid superlattice nanohelices of ZnO have been discovered, which is a result of minimization of the electrostatic energy induced by polar surfaces. The formation process of the nanohelix has been systematically characterized. Thirdly, two new strategies have been successfully developed for fabricating ZnO quantum dots and synthesis of ZnO nanodiskettes and nanotubes. The formation process is based on a common concept of self-assembly. Finally, a series of devices and applications studies based on several piezoelectric ZnO nanostructures, such as nanobelts, nanopropellers and nanohelices, have been carried out utilizing the electro-mechanical resonance, bio-surface functionalization, devices fabrication and electrical characterization. Individual nanobelt and nanohelix based nanodevices have been successfully fabricated for applications in chemical and biological sensing. The study opens a few new areas in oxide nanostructures and applications.