Thesis: M.S., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 1975 / Includes bibliographical references. / M.S. / M.S. Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science

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No description available.

M. S.

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Requirements exist for a unique type of underwater acoustic source. The transducer is in the form of a linear array of discrete elements and is required to have a constants transmitting voltage response and carefully controlled directivity characteristics over a two octave bandwidth. A generalized model of a linear array of cylindrical piezoelectric ceramic acoustic radiators is developed and applied to the design of a prototype which operates over approximately one half of the required bandwidth. The prototype transducer was built and the measured results are compared with those predicted by the model. Recommendations are made for improving the performance of both the prototype and the array required to meet the full bandwidth specified.

Ionic polymer transducers comprise a class of active material that exhibit interesting chemoelectromechanical coupling capabilities. With the ability to convert energy between chemical, electrical and mechanical domains, these materials offer potential for use in numerous engineering applications. The research presented in this dissertation focuses primarily on the electromechanical coupling that exists within these ionic polymer materials. When plated with a conductive surface electrode, these ionomeric membranes function effectively as either sensors or actuators. Mechanically compliant, these transducers demonstrate large strain, but limited force, capabilites while operating at low excitation voltages. The objective of this research is to improve understanding of the transduction properties inherent in the ionic polymer. Most of the existing work in this area has focused on the actuation response, therefore the focus of this research is on providing a better understanding of the sensing and impedance responses of the ionic polymer transducer. Using transport theory as the basis, a set of analytical models are developed to characterize the charge motion that develops within an ionomer when subject to either mechanical or electrical loading. These models characterize the internal potential and charge density responses of the membrane, as well as the expected surface current that would be measured as the result of external loading. In addition to the analytical work, numerous experimental characterizations of the membrane are also presented. The ionic polymer's actuation, sensing and impedance responses are each considered as a function of the counterion and solvent type present within the ionic polymer. These studies demonstrate the importance of the ionomer's impedance response in understanding the electromechanical capabilites of an ionic polymer transducer. Most sample-to-sample variation can be attributed to the voltage to current conversion that occurs within the ionic polymer. By relating these experimental results to the analytical models, it is possible to characterize these changes in performance in terms of the effective diffusion and permittivity parameters of the transducer. A final series of experiments are also considered to determine the effectiveness of the model in predicting the impedance response as a function of temperature, solvent viscosity and preloading of the membrane. / Ph. D.

Electro-active polymers (EAPs) have emerged as a new class of active materials, which produce large deformations in response to an electric stimulus. EAPs have attractive characteristics of being lightweight, inexpensive, stretchable, and flexible. Additionally, EAPs are conformable, and their properties can be tailored to satisfy a broad range of requirements. These advantages have enabled many target applications in actuation and sensing. A general constitutive formulation for isotropic and anisotropic electro-active materials is developed using continuum mechanics framework and invariant theory. Based on the constitutive law, electromechanical stability of the electro-elastic materials is investigated using convexity and polyconvexity conditions. Implementation of the electro-active material model into a commercial finite element software (ABAQUS 6.9.1, PAWTUCKET, RI, USA) is presented. Several boundary and initial value problems are solved to investigate the actuation and sensing response of isotropic and anisotropic dielectric elastomers (DEs) subject to combined mechanical and electrical loads. The numerical response is compared with experimental results to validate the theoretical model. For the constitutive formulation of the electro-elastic materials, invariants for the coupling between two families of electro-active fibers (or particles) and the applied electric field are introduced. The effect of the orientation of the electro-active fibers and the electric field on the electromechanical coupling is investigated under equibiaxial extension. Advantage of the constitutive formulation derived in this research is that the electromechanical coupling can be illustrated easily by choosing invariants for the deformation gradient tensor, the electro-active fibers, and the electric field. For the electromechanical stability, it is shown that the stability can be controlled by tuning the material properties and the orientation of the electro-active fibers. The electromechanical stability condition is useful to build a stable free energy function and prevent the instabilities (wrinkling and electric breakdown) for the electro-elastic materials. The invariant-based constitutive formulation for the electro-elastic materials including the isotropic and anisotropic DEs is implemented into a user subroutine (UMAT in ABAQUS: user defined material) by using multiplicative decomposition of the deformation gradient and the applicability of the UMAT is shown by simulating a complicated electromechanical coupling problem in ABAQUS/CAE. Additionally, the static and dynamic sensing and actuation response of tubular DE transducers (silicone and polyacrylate materials) with respect to combined electrical and mechanical stimuli is obtained experimentally. It is shown that the silicone samples have better dynamic and static sensing characteristics than the polyacrylate. The theoretical modeling accords well with the experimental results. / Ph. D.

This dissertation is concerned with the evaluation of a new statistically sound reconstruction methodology for continuous 3-D dynamic response fields of harmonically excited structures in steady-state vibration. This results in an experimental process which reconstructs the response field from a set of 3-D projections based on Laser-Doppler-Vibrometer (LDV) localized instantaneous velocity measurements. Included along with an estimate of the 3-D velocity field, are its statistical characteristics and the inferential tools required to test the quality of the estimation. This dissertation documents in detail the development and evaluation of the proposed reconstruction methodology and its relevant subprocesses which inc1ude the formulation of a deterministic laser-structure kinematic model, and regression models that afford statistical inference for the time-domain and spatial-domain structural dynamics, as well as for the projection recombination process. / Ph. D.