Browsing by Subject "Piezoelectric"
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Item Analysis of piezoelectric thin film energy harvester for biomedical application(2014-05) Ha, Taewoo; Zhang, John X.J.; Lu, NanshuThe effect of the thickness ratio variation of a unimorph piezoelectric energy harvester to the electric output under bending condition is studied. The harvester forms a blanket with PVDF-TrFE as an energy harvesting layer and Kapton film used as a substrate. The thickness of Kapton is fixed as 25um while the thickness of PVDF-TrFE is varied from 0.5 um to 20um. The voltage, charge and energy output are estimated by numerical and theoretical method under three different bending conditions with fair biomedical model. For all conditions, the Young's modulus ratio changes the optimal point of all outputs. The effect of surface patterning is studied with regard to the rib-base thickness ratio and the rib-spacing ratio. The voltage and electric energy output falls with the decrease of the base-rib thickness ratio. The charge output rises with the decrease of the base-rib thickness ratio. However, the charge increasing rate is smaller than the voltage decreasing rate. Hence, the electric energy decreasing rate is mostly affected by the voltage decreasing rate. By changing rib-spacing ratio, the electric energy output of the grated structure can be enhanced. If the piezo-substrate thickness ratio is larger than a specific value, the grated structure is more efficient than the planar structure. A recent study from Ran Liu group asserts that the piezoelectric effect becomes electrostatically stronger at the singularity point of the nano imprinted structure where the bending induced stress is also concentrated. Thereby, the grated structure would enhance the electric energy output of the energy harvester. Overall, this research will contribute to design optimal thin film energy harvester for biomedical application.Item A comparison of models for a piezoelectric 31-mode segmented cylindrical transducer(2013-12) Joseph, Nicholas John; Wilson, Preston S.; Haberman, Michael R.Piezoelectric transducers with cylindrical geometry are often designed to operate in a radial “breathing” mode. In order to tune their performance in a cost effective way, cylinders can be constructed of alternating active (piezoelectric) and inactive (non-piezoelectric) staves. Existing lumped parameter models for such a ring are based on effective piezoelectric properties of the composite ring which reduce the system to a single degree of freedom corresponding to the breathing motion. Unfortunately, if the length of the staves is a sufficiently large percentage of the circumference, the transducer may demonstrate a detrimental higher frequency resonance within the desired bandwidth of operation even when all staves are uniformly excited by an electrical field. This parasitic resonance results from bending motion of the staves associated with stiffness and mass discontinuities of the constituent material properties and can significantly decrease the radiated acoustic pressure and generate distortion of the radiated acoustic waveform. This work presents a multiple-degree-of-freedom lumped parameter model that captures both the breathing and bending resonances of the transducer and provides a more accurate prediction of its effective coupling coefficient. Results are compared with a one-degree-of-freedom model, finite element models, and experimental data. Modifications to account for internal volumes, nonlinearities, and other effects are also presented and discussed.Item A computational procedure for analysis of fractures in two-dimensional multi-field media(2010-12) Tran, Han Duc; Mear, Mark E.; Rodin, Gregory J.; Ravi-Chandar, Krishnaswa; Landis, Chad M.; Tassoulas, John L.A systematic procedure is followed to develop singularity-reduced integral equations for modeling cracks in two-dimensional, linear multi-field media. The class of media treated is quite general and includes, as special cases, anisotropic elasticity, piezoelectricity and magnetoelectroelasticity. Of particular interest is the development of a pair of weakly-singular, weak-form integral equations (IEs) for "generalized displacement" and "generalized stress"; these serve as the basis for the development of a Symmetric Galerkin Boundary Element Method (SGBEM). The implementation is carried out to allow treatment of general mixed boundary conditions, an arbitrary number of cracks, and multi-region domains (in which regions having different material properties are bonded together). Finally, a procedure for calculation of T-stress, the constant term in the asymptotic series expansion of crack-tip stress field, is developed for anisotropic elastic media. The pair of weak-form boundary IEs that is derived (one for generalized displacement and the other one for generalized stress) are completely regularized in the sense that all kernels that appear are (at most) weakly-singular. This feature allows standard Co elements to be utilized in the SGBEM, and such elements are employed everywhere except at the crack tip. A special crack-tip element is developed to properly model the asymptotic behavior of the relative crack-face displacements. This special element contains "extra" degrees of freedom that allow the generalized stress intensity factors to be directly obtained from the solution of the governing system of discretized equations. It should be noted that while the integral equations contain only weakly-singular kernels (and so are integrable in the usual sense) there remains a need to devise special integration techniques to accurately evaluate these integrals as part of the numerical implementation. Various examples for crack problems are treated to illustrate the accuracy and versatility of the proposed procedure for both unbounded and finite domains and for both single-region and multi-region problems. It is found that highly accurate fracture data can be obtained using relatively course meshes. Finally, this dissertation addresses the development of a numerical procedure to calculate T-stress for crack problems in general anisotropic elastic media. T-stress is obtained from the sum of crack-face displacements which are computed via a (regularized) integral equation of the boundary data. Two approaches for computing the derivative of the sum of crack-face displacements are proposed: one uses numerical differentiation, and the other one uses a weak-form integral equation. Various examples are examined to demonstrate that highly accurate results are obtained by means of both approaches.Item Design and comparison of single crystal and ceramic Tonpilz transducers(2010-08) Nguyen, Kenneth Khai; Haberman, Michael R.; Wilson, Preston S.; Hall, Neal A.Transducers utilizing single crystal piezoelectrics as the active elements have been shown to exhibit broader operating bands, higher response levels, and higher power efficiency than transducers using piezoceramics while also reducing the size and mass of the transducer (Moffett et al., J. Acoust. Soc. Am., 2007). The key to these high performance characteristics is the piezocrystal's inherent high electromechanical coupling coefficient. One potential application is to replace multiple narrowband piezoceramic transducers with a single broadband piezocrystal transducer which reduces the system's weight and size. This is very important for the new generation of smaller and power efficient unmanned underwater vehicles (UUVs). A third application is for use in very broadband communication networks. The work presented here focuses specifically on the design, modeling, and construction of Tonpilz transducers using piezoelectrics as the active material. The modeling includes lumped element and finite element analysis to approximate the performance of these transducers. These models serve as the main structure of an overall iterative design process. The objective of this research is to compare the performance characteristics of a piezocrystal and a piezoceramic Tonpilz transducer and to validate the models by comparing the model predictions with experimental results.Item Design and testing of piezoelectric sensors(2009-05-15) Mika, BartoszPiezoelectric materials have been widely used in applications such as transducers, acoustic components, as well as motion and pressure sensors. Because of the material?s biocompatibility and flexibility, its applications in biomedical and biological systems have been of great scientific and engineering interest. In order to develop piezoelectric sensors that are small and functional, understanding of the material behavior is crucial. The major objective of this research is to develop a test system to evaluate the performance of a sensor made from polyvinylidene fluoride and its uses for studying insect locomotion and behaviors. A linear stage laboratory setup was designed and built to study the piezoelectric properties of a sensor during buckling deformation. The resulting signal was compared with the data obtained from sensors attached a cockroach, Blaberus discoidalis. Comparisons show that the buckling generated in laboratory settings can be used to mimic sensor deformations when attached to an insect. An analytical model was also developed to further analyze the test results. Initial analysis shows its potential usefulness in predicting the sensor charge output. Additional material surface characterization studies revealed relationships between microstructure properties and the piezoelectric response. This project shows feasibility of studying insects with the use of polyvinylidene fluoride sensors. The application of engineering materials to insect studies opens the door to innovative approaches to integrating biological, mechanical and electrical systems.Item Design, fabrication, and testing of a MEMS z-axis Directional Piezoelectric Microphone(2012-05) Kirk, Karen Denise; Hall, Neal A.; Neikirk, Dean P.Directional microphones, which suppress noise coming from unwanted directions while preserving sound signals arriving from a desired direction, are essential to hearing aid technology. The device presented in this paper abandons the principles of standard pressure sensor microphones, dual port microphones, and multi-chip array systems and instead employs a new method of operation. The proposed device uses a lightweight silicon micromachined structure that becomes “entrained” in the oscillatory motion of air vibrations, and thus maintains the vector component of the air velocity. The mechanical structures are made as compliant as possible so that the motion of the diaphragm directly replicates the motion of the sound wave as it travels through air. The microphone discussed in this paper achieves the bi-directionality seen in a ribbon microphone but is built using standard semiconductor fabrication techniques and utilizes piezoelectric readout of a circular diaphragm suspended on compliant silicon springs. Finite element analysis and lumped element modeling have been performed to aid in structural design and device verification. The proposed microphone was successfully fabricated in a cleanroom facility at The University of Texas at Austin. Testing procedures verified that the resonant frequency of the microphone, as expected, was much lower than in traditional microphones. This report discusses the theory, modeling, fabrication and testing of the microphone.Item Harvesting wind energy using a galloping piezoelectric beam(2011-05) Mahadik, Rohan Ram; Sirohi, Jayant; Bennighof, JeffreyGalloping of structures such as transmission lines and bridges is a classical aeroelastic instability that has been considered as harmful and destructive. However, there exists potential to harness useful energy from this phenomenon. The study presented in this paper focuses on harvesting wind energy that is being transferred to a galloping beam. The beam has a rigid prismatic tip body. Triangular and D-section are the two kinds of cross section of the tip body that are studied, developed and tested. Piezoelectric sheets are bonded on the top and bottom surface of elastic portion of the beam. During galloping, vibrational motion is input to the system due to aerodynamic forces acting on the tip body. This motion is converted into electrical energy by the piezoelectric (PZT) sheets. A potential application for this device is to power wireless sensor networks on outdoor structures such as bridges and buildings. The relative importance of various parameters of the system such as wind speed, material properties of the beam, electrical load, beam natural frequency and aerodynamic geometry of the tip body is discussed. A model is developed to predict the dynamic response, voltage and power results. Experimental investigations are performed on a representative device in order to verify the accuracy of the model as well as to study the feasibility of the device. A maximum output power of 1.14 mW was measured at a wind velocity of 10.5 mph.Item Low Power High Efficiency Integrated Class-D Amplifier Circuits for Mobile Devices(2015-01-12) Colli-Menchi, Adrian IsraelThe consumer?s demand for state-of-the-art multimedia devices such as smart phones and tablet computers has forced manufacturers to provide more system features to compete for a larger portion of the market share. The added features increase the power consumption and heat dissipation of integrated circuits, depleting the battery charge faster. Therefore, low-power high-efficiency circuits, such as the class-D audio amplifier, are needed to reduce heat dissipation and extend battery life in mobile devices. This dissertation focuses on new design techniques to create high performance class-D audio amplifiers that have low power consumption and occupy less space. The first part of this dissertation introduces the research motivation and fundamentals of audio amplification. The loudspeaker?s operation and main audio performance metrics are examined to explain the limitations in the amplification process. Moreover, the operating principle and design procedure of the main class-D amplifier architectures are reviewed to provide the performance tradeoffs involved. The second part of this dissertation presents two new circuit designs to improve the audio performance, power consumption, and efficiency of standard class-D audio amplifiers. The first work proposes a feed-forward power-supply noise cancellation technique for single-ended class-D amplifier architectures to improve the power-supply rejection ratio across the entire audio frequency range. The design methodology, implementation, and tradeoffs of the proposed technique are clearly delineated to demonstrate its simplicity and effectiveness. The second work introduces a new class-D output stage design for piezoelectric speakers. The proposed design uses stacked-cascode thick-oxide CMOS transistors at the output stage that makes possible to handle high voltages in a low voltage standard CMOS technology. The design tradeoffs in efficiency, linearity, and electromagnetic interference are discussed. Finally, the open problems in audio amplification for mobile devices are discussed to delineate the possible future work to improve the performance of class-D amplifiers. For all the presented works, proof-of-concept prototypes are fabricated, and the measured results are used to verify the correct operation of the proposed solutions.Item Monitor and control of cockroach locomotion with piezoelectric sensors(2009-05-15) Cooper, Rodrigo AlejandroMonitoring and controlling of insects are of great scientific and engineering interests based on the potential impacts on environments, search and rescue operations, and robotics design. This research focuses on studying insects? locomotive behavior by employing noninvasive piezoelectric sensors and presenting a conceptual method of locomotion control. To do so, polyvinylidene fluoride thin sheets are used as bending sensors at the joints of a cockroach?s legs. Approaches include development of polymeric sensors; laboratory in vitro testing of sensors and cockroaches; and methodology to control them. This research successfully built an experimental foundation for sensor and roach testing and developed a methodology for roach locomotion control. This research links engineering and entomology potentially having impacts in the mentioned arenas. Testing showed that piezoelectric films, such as polyvinylidene fluoride (PVDF), can serve as motion sensors for the legs, providing frequency and range of motion of each of the roach?s legs. The film is thin enough to provide as little resistance to motion to prevent altering the roach?s natural walking patterns. Testing also showed that using the insect?s instinct to physically touch an unknown object can be used as a directional control method. By using this natural response, a device can be fit on the roach capable of guiding the roach in any direction desired. This thesis is organized to present a brief introduction on the history and need for biomimetic robots. This section is followed by the research objectives and an introduction to polyvinylidene fluoride and the piezoelectric properties that allow it to become a sensor. A brief description of the roach anatomy and physiology is presented that will provide baseline of information needed to proceed with the project. We finish with an explanation of the testing of sensors on the roach and a novel method to control the roach walking orientation.Item Phase-field modeling of fracture for multiphysics problems(2016-12) Wilson, Zachary Adam; Landis, Chad M.; Hughes, Thomas J.R.; Mear, Mark E.; Ravi-Chandar, Krishnaswa; Foster, John T.Several recent works have demonstrated that phase-field methods for modeling fracture are capable of yielding complex crack evolution patterns in materials. This includes the nucleation, turning, branching, and merging of cracks subject to a variety of quasi-static and dynamic loadings. What follows will demonstrate how phase-field methods for fracture can be applied to problems involving materials subject to electromechanical coupling and the problem of hydraulic fracture. Brittle fracture is a major concern in piezoelectric ceramics. Fracture propagation in these materials is heavily influenced by the mechanical and electrical fields within the material as well as the boundary conditions on the crack surfaces. These conditions can lead to complex multi-modal crack growth. We develop a continuum thermodynamics framework for a damaging medium with electromechanical coupling subject to four different crack-face boundary conditions. A theory is presented to reproduce impermeable, permeable, conducting, and energetically consistent crack-face boundary conditions, the latter of which requires a finite deformation formulation. A primary application of hydraulic fracturing involves the injection of fluid into a perforated wellbore with the intention of fracturing the surrounding reservoir and stimulating its overall production. This process involves the coupling of fluid flow with material failure, which must account for the interactions of several cracks, both natural and man-made. Many of the questions on the effects these interactions have on the performance of the frac treatments are unanswered. We develop a continuum thermodynamics framework for fluid flow through a damaging porous medium in order to represent some of the processes and interactions that occur during hydraulic fracturing. The model will be capable of simulating both Stokes flow through cracks and Darcy flow through the porous medium. The flow is coupled to the deformation of the bulk solid medium and the evolution of cracks within the material. We utilize a finite deformation framework in order to capture the opening of the fractures, which can have substantial effects on fluid pressure response. For both models, a fully coupled non-linear finite element formulation is constructed. Several benchmark solutions are investigated to validate the expected behavior and accuracy of the method. In addition, a number of interesting problems are investigated in order to demonstrate the ability of the method to respond to various complexities like material anisotropy and the interaction of multiple cracks.Item Piezoelectric Artificial Kelp: Experimentally Validated Parameter Optimization of a Quasi-Static, Flow-Driven Energy Harvester(2011-10-21) Pankonien, Alexander MorganPiezoelectric energy harvesting is the process of taking an external mechanical input and converting it directly into electrical energy via the piezoelectric effect. To determine the power created by a piezoelectric energy harvester, a specific application with defined input and design constraints must first be chosen. The following thesis established a concept design of a hydrokinetic energy harvesting system, the piezoelectric artificial kelp (PAK), which uses piezoelectric materials to harvest coastal ocean waves while having a beneficial impact on the surrounding environment. The harvester design mimics the configuration of sea-kelp, a naturally occurring plant that anchors to the ocean floor and extends into the water column. Underwater currents caused by wave-action result in periodic oscillations in the kelp. In order to determine the average power generated by this design concept, predictive tools were devised that allowed for the determination of the optimized average power produced by the piezoelectric energy harvester. For a stiff energy harvester, the linear differential equations were analytically solved to find an equation for the average power generated as a function of design parameters. These equations were used to compare the effect on power output of the design configuration and piezoelectric material choice between a piezopolymer (PVDF) and a piezoceramic (PZT). The homogeneous bimorph was found to have the optimal design configuration and it was shown that a harvester constructed using PVDF would produce approximately 1.6 times as much power as one using PZT. For a flexible energy harvester, an iterative nonlinear solution technique using an assumed polynomial solution for the local curvature of the energy harvester was used to verify and extend the analytic solutions to large deflections. An energy harvester was built using off-the-shelf piezoelectric elements and tested in a wave tank facility to validate experimentally the voltage and average power predicted by the analytical solution. The iterative code showed the PAK harvester to produce volumetric power on the order of other energy harvesting concepts (17.8 micro [mu]W/cm?). Also, a full-scale PAK harvester approximately ten meters long in typical wave conditions was found to produce approximately one watt of power.Item Synthesis and Characterization of Piezo-Magneto (PVDF-Fe3O4) Composites(2012-07-16) Mulamba, Oliver KasongoThis research entails the synthesis and characterization of a novel class of materials which incorporate both magnetic and piezoelectric characteristics. The composite is made up of the piezoelectric polymer PVDF and magnetic nanoparticles. The testing samples are produced using a spin casting process. The characterizations of the samples were performed using X-ray diffraction, Atomic force microscopy, linear staging, Dynamic mechanical analysis, Differential scanning calorimetry, and Fourier transform Infra-Red. X-ray diffraction and Atomic force microscopy showed that the presence of the Fe3O4 particles have no effect on the crystallinity of the polymer matrix, therefore allowing for the incorporation of inclusions without directly affecting the piezoelectric property. Changes in the thermal characteristics of the polymer matrix, observed using Differential scanning calorimetry, indicated increases in the thermal conductivity of the composite. Decreases in the heat of melting and crystallization were also observed and further solidified the conclusion that the presence of the Fe3O4 nanoparticles changes the thermal behavior of the polymer. It was observed from the DMA results caused an increase in the storage modulus of the polymer matrix which is related to an increase in the material's ability to store energy. Linear staging results showed that the presence of the nanoparticles had an effect on the mechanical properties of the composites and altered the time dependent voltage output readings. These results were used to calculate the energy capabilities of the composite material and it was found that the composites showed greater energy outputs with increasing amounts of nanoparticles. Interaction was observed between the embedded particles and an external magnetic field, which was found to decrease the energy outputs of the composites. This research showed enhancements in the composite material's energy outputs in comparison to the pure PVDF samples. This research also showed that the embedded nanoparticles interacted with an exteriorly applied magnetic field. This observation introduces a new dimension of possible activation processes for piezoelectric devices which have been largely based on physical forms of activation. PVDF which is widely used in research and applications for its superior output capabilities has been enhanced in this research and shown to have capabilities to exhibit higher energy outputs.Item Using piezoelectric technology to harvest energy from drums and inspire an engaging high school classroom experience(2012-08) Earnhart, Alison; Crawford, Richard H.; Wilson, Preston S.Using piezoelectric materials to harvest the energy of vibration is a popular and fast-growing field of study. This report details an attempt to use piezoelectric energy harvesting techniques to support an interesting and engaging lab experience for high school engineering students in which the vibration of musical instruments (specifically drums, for this report) is harnessed to power a string of decorative LEDs. The likelihood of the energy harvesting actually being successful enough to light the LEDs was not known before undertaking this lab, so the goals of the project became twofold: 1. Conduct the experiment from scratch to determine if a substantial amount of energy can be harvested from the instruments (enough to reach the goal of lighting the LEDs), and 2. Identify how this lab experience (or one similar to it, if the goal of lighting the LEDs is unattainable) can be beneficial to high school engineering students. The purpose of this report is to summarize the research that was carried out to harvest energy from drums using piezoelectric technology, and to outline how similar lab exercises can be utilized in the high school engineering classroom setting.