Browsing by Subject "Transducers"
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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 Nonlinear control of an electrostatically actuated MEMS(Texas Tech University, 2003-12) Maithripala, SanjeevaOf the wide variety of actuation methods that have been developed for microelectromechanical systems (MEMS), electrostatic devices are the most common. The operation of these devices may be primarily categorized as digital and analog. Although the technology in digital operations is quite well developed the analog operations are not as developed due to an inherent nonlinear phenomenon in electrostatic actuation commonly known as "snap-through" "or pull-in." The concern of this thesis is analog control of electrostatically actuated MEMS devices. A simple 1-D model of electrostatic actuation is sufficient to capture the salient nonlinearities of the general problem. Several analog control schemes for such a model are proposed in the literature based on physical intuition. In the first part of the dissertation we show how these control schemes can be derived from the application of standard nonlinear control theory. Then we employ notions of feedback linearization, passivity and nonlinear state estimation to derive much improved control schemes that eliminates snap-through, improve performance with respect to low overshoot and faster settling times. The second part of the dissertation is concerned with generalizing the analog control notions developed for the 1-D model to a 3-D model where the device is assumed to freely rotate as well as translate. We first note that the system can be perceived as a coupled electromechanical system where the configuration space of the mechanical subsystem is the special Euclidian motion group SE{S). Thus we approach the problem from the setting of finding intrinsic control strategies for mechanical systems on general Lie groups. Furthermore, we do it in such a way that no coordinates need to be introduced on the Lie group. Thus, apart from the simplicity it provides, the tools developed in here may be of great importance to long term trajectory planning and optimal control problem on Lie groups and stabilization and active vibration absorption of rigid 3-D structures.