# 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, NanshuShow more The 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.Show more Item A comparison of models for a piezoelectric 31-mode segmented cylindrical transducer(2013-12) Joseph, Nicholas John; Wilson, Preston S.; Haberman, Michael R. (Michael Richard), 1977-Show more 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.Show more 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.Show more 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.Show more Item Design and comparison of single crystal and ceramic Tonpilz transducers(2010-08) Nguyen, Kenneth Khai; Haberman, Michael R. (Michael Richard), 1977-; Wilson, Preston S.; Hall, Neal A.Show more 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.Show more Item Design, fabrication, and evaluation of a biologically-inspired piezoelectric MEMS microphone with in-plane directivity(2019-12) Stalder, Carly Amanda; Hall, Neal A.Show more This work examines the directional hearing capabilities of the fly Ormia ochracea and how they are applied to microelectronics. The fly can auditorily determine the direction of a cricket chirp, though the wavelength of the chirp is more than ten times longer than the length of the fly's hearing mechanism. The design, modeling, fabrication, and evaluation of a microphone that harnesses this fly's hearing ability are explored. The device consists of a two-sided cantilever beam that rotates about torsional pivots located along the y-axis. The result is two main frequency modes that can be used in the sound localization process for in-plane directivity in the x-direction: a gradient mode that causes opposite ends of the beam to move out-of-phase, and a symmetrical mode that causes the ends of the beam to move in-phase. Springs connect the free ends of the beam to the center pivot. Strain in these springs is converted to a voltage at the output. The microphones are fabricated on a silicon-on-insulator wafer with a 2 μm-thick device layer and 500 nm-thick aluminum nitride film as the piezoelectric transduction material. The active beam measures 500 x 250 μm², which approaches the dimensions of the fly's ear and is the smallest version of the microphone to date. The sensing modes are modeled with finite element analysis and confirmed in multipoint scans. Preliminary directivity measurements are made to demonstrate the directional capabilitiesShow more Item Design, fabrication, and testing of a MEMS z-axis Directional Piezoelectric Microphone(2012-05) Kirk, Karen Denise; Hall, Neal A.; Neikirk, Dean P.Show more 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.Show more Item Evaluating piezoelectric constant d₃₁ of films deposited on silicon using low frequency-actuated piezoelectric cantilever structures(2018-12-07) Corona, Daniel William; Hall, Neal A.Show more Piezoelectric coefficients of films deposited on silicon are surprisingly expensive to measure using experiments commonly found in literature. A low-cost method of approximating the small-signal piezoelectric coefficient d₃₁ for a film by comparing data from a single laser-doppler vibrometer measurement and a numerical model is presented. This method is useful for directly evaluating the quality of a piezoelectric film. Relevant properties of piezoelectric materials are introduced, and pitfalls of prior testing methods are discussed. An analytical model of the test is developed to provide insight into critical test parameters. The test is validated by comparing the numerical and the analytical model, by comparing experimental results to film x-ray diffractometry measurements, and by building opportunities for validation into the experiment. Explicit experimental validation is deemed too expensive and unnecessary for the immediate needs of the author. The method is also applied to evaluate the piezoelectric properties of several AlN films developed using varying fabrication parameters. Results are used to improve the fabrication process of an AlN film on silicon for use in piezoelectric sensor prototypesShow more Item Harvesting wind energy using a galloping piezoelectric beam(2011-05) Mahadik, Rohan Ram; Sirohi, Jayant; Bennighof, JeffreyShow more Galloping 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.Show more Item Material property extraction procedure for electromomentum coupled metamaterials(2023-08) Casali, Matthew A.; Haberman, Michael R. (Michael Richard), 1977-Show more Electromomentum (Eμ) coupling is a material response that couples the macroscopically observable time-varying electric field to the momentum of the material. This unique behavior has been shown theoretically to result from dynamics at subwavelength length-scales due to asymmetries in heterogeneous piezoelectric materials. Electromomentum coupling is of interest to the engineering and scientific community for its ability to simultaneously sense both the acoustic pressure and particle velocity at a single point in space, thus enabling the creation of vector sensor devices using a single material. This thesis presents a study of the characterization of this novel transduction behavior through multiscale models and numerical experiments. The material models include analytical and finite element methods that extend the work of Pernas-Salomón et al. [Wave Motion, 106, 102797, (2021)]. The models simultaneously provide insight into the subwavelength behavior that leads to Eμ coupling on the macroscopic scale as well as metrics of the coupling strength. Additionally, these models are employed in a design strategy to maximize Eμ coupling demonstrated by a heterogeneous piezoelectric scatterer using readily available materials and easily manufactured geometries. To achieve this, a series of candidate designs are modeled and their Willis and/or Eμ coupling is quantified. The models are then employed to design an experimental method to characterize Eμ coupling of a sample using a water-filled impedance tube. The impedance tube measurement procedure presented in this work is a generalization of existing methods used to infer the frequency-dependent material properties of a sample from measurements of its scattering coefficients and associated property extraction algorithms. Namely, the works of Song and Bolton to measure the complex impedance and wavenumber or phase speed and attenuation [J. Acoust. Soc. Am., 107(3), pp. 1131-1152, (2000)], Fokin et al. to measure the complex-valued density and bulk modulus, including negative values, [Phys. Rev. B, 76(14), 114302, (2007)], and Muhlestein et al. who extended the work of Fokin et al. to measure Willis coupling in addition to density and bulk modulus [Nat. Commun., 8, 15625, (2017)]. This work also considers practical details such as dispersion, hydrophone calibration, and sample mounting, that are specific to measurements in a water-filled impedance tube and their influence on the accuracy of measurements of scattering coefficients using this apparatus, ending with recommendations for future measurements.Show more 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.Show more 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.Show more 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.Show more 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.Show more