Browsing by Subject "Piezoelectricity"
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Item A study into the application of piezoelectrics to modify ankle torques in active prosthetic feet using finite element analysis(2012-05) Powelson, Thomas; Yang, Jingzhou; Tate, Derrick; Ekwaro-Osire, StephenOver the last fifty years there has been a steady advance in prosthetic foot technologies. These advances have primarily focused on more accurately mimicking the biologic foot for amputees. One eld of research currently being explored is active/powered prosthetic feet in which the movement of the foot is actively controlled through the use of electric motors. Some of these feet also seek to reproduce the ankle torques seen in the biologic foot. This thesis proposes to investigate the possibility of the integration of piezoelectrics into active prosthetic feet to more accurately reproduce these ankle torques. A general set of FEA models, simulations, and analysis tools have been developed for the design and testing of applications involving piezoelectric beam bending actuators. These tools were utilized to successfully replicate the ankle torques versus time pro les found in the literature through the application of a number of di erent con gurations of piezoelectric strips. It was found that while it was possible to replicate these toques with piezoelectrics alone, the required voltages were far too large to be practical.Item Development of a variable frequency heterodyne sonication system(Texas Tech University, 2004-05) Korremula, Bhanu KiranAlmost all available instruments used in sonochemistry produce ultrasound at a fixed frequency. There is no commercially available instrument which produces ultrasound at a wide range of frequencies. The main problems in making such an instrument is that ceramic's characteristics change widely with frequency, and it is consequently difficult to develop a drive circuitry which drives the instrument over a wide range of frequencies. The instrument designed in this thesis is unique because it produces ultrasound over the frequency range from 150 kHz to 500 kHz for use in sonochemical studies. The lossless matching circuit designed here successfully matches the complicated variations of the impedance of the ceramic over the above frequency range, thus making the instrument very versatile . The instrument has two transducers, so that frequency as well as heterodyne effects can be examined. In the Variable Frequency Heterodyne Sonication System, two waves of different frequencies are produced and sent into the glass cell. Heterodyne components are expected to produce more sonochemical reaction sites and hence ultimately to lead to increased cavitation collapse efficiency. Calorimetric and chemistry experiments were performed. Frequency and heterodyne effects were examined.Item The effect of a piezoelectric perturbation on the spray distribution of an atomizing jet(Texas Tech University, 1990-08) Fernandez, Melvyn LThe effect of a finite, piezoelectrically induced, perturbation on the characteristics of a fluid stream was investigated in this study. The fluid stream characteristics considered were the mean drop size and the standard deviation of the spray distribution. Three parameters were considered to affect the spray distribution in this investigation: static supply pressure; frequency of the piezoelectric disturbance; and the amplitude of the piezoelectric disturbance. Mean and standard deviation data were collected for amplitudes of 6 and 15 volts. For each amplitude, all combinations of frequencies of 0, 250, 500, 750, 800, 900, 950, and 1000 kHz and pressures of 100, 200, 300, 400, 500 and 600 psi were used. Similarly, data were collected for frequencies of 500 and 1000 kHz, for all combinations of amphtudes of 0, 3, 6, 9, 12, and 15 volts and the same range of pressures. Experimental results show that there is a definite decrease in the mean and standard deviation of a spray distribution with an increase in pressure. Also, at pressures of 400, 500 and 600 psi the standard deviation decreased with higher amplitudes and frequencies. At 100 psi there was no effect of either frequency or amplitude on the mean and standard deviation of the spray distribution.