No description available.

This document only includes an excerpt of the corresponding thesis or dissertation. To request a digital scan of the full text, please contact the Ruth Lilly Medical Library's Interlibrary Loan Department (rlmlill@iu.edu).

In the first section, the thickness of ice on the lakes and canals is estimated by analyzing the sound spectrum generated by dispersion of Lamb type waves propagating in ice. In winters when the lakes and canals freeze, it is important to know the thickness of the ice layer before setting foot on it. When a stone is thrown on the ice layer, a fluting sound can be heard. This is recorded for different thicknesses of ice, and the sound spectrum is compared with the results simulated using a parameterized model. This model is created using a combination of plane waves for different incident angles and frequencies to generate dispersion curves for different thicknesses of ice. The frequencies of the reflected sound are then compared with the frequencies of musical instruments in order to assign different musical notes to different thicknesses of ice. The technique enables thickness estimation without the use of specialized equipment or time consuming drilling and may therefore be of practical value in the preservation of the lives of ice skaters and playing children. In the second half of the study, high frequencies (400 MHz and 1 GHz) are used to investigate samples with micro structures. Acoustic microscopy is a well established technique as far as smooth surfaces are concerned. V (z) curves are obtained from which, through surface wave generation, important features concerning elasticity and related properties can be extracted. Recently, high resolution imaging using high frequency focused transducers, based on acoustic microscopy has appeared. The surface profiles of the samples used in this study, have periodic structures but lack smoothness. The periodicity causes sound diffraction and the roughness influences the acoustic microscopic investigation. The small acoustic contrast between the substrate and the periodic corrugation on the material, gives us information about the additional stresses which develop and affect the bonding between the two materials. In this study, experiments are conducted using samples with corrugations of different periodicity, and a comparison is made between the results for smoother surfaces and results for the periodic structures of the same material. An attempt is made to analyse the effects described above.

No description available.

Acoustic metamaterials are sub-wavelength structures designed to overcome limitations in the material properties of conventional materials. The present research focuses on the nonlinear acoustic and dynamic response of a specific type of engineered microstructure called a snapping acoustic metamaterial (SAMM). Snapping of these elements is defined as large, rapid deformations induced by infinitesimal perturbations in the time-varying external pressure. Snapping behavior in SAMM elements results from their non-monotonic stress-strain response, which displays regimes of positive and negative stiffness. This work presents a modeling study of the nonlinear behavior of both individual SAMM elements and a heterogeneous material containing a dilute concentration of SAMM elements embedded in a nearly incompressible viscoelastic solid. Two different scenarios are considered: (i) nonlinear wave propagation in the heterogeneous medium, and (ii) forced nonlinear dynamics of inclusions embedded in a viscoelastic medium. The nonlinearity of the SAMM elements is represented by a cubic pressure-volumetric strain relationship based on finite element model results from previous work. The effective nonlinear response of a heterogeneous mixture of SAMM elements embedded in a matrix, characterized by the parameters B/A and C/A, is then determined using both a nonlinear mixture law and a nonlinear Hashin-Shtrikman approach. The former estimate is limited to matrix materials with zero shear modulus, which cannot stabilize SAMM inclusions in regimes of negative stiffness. The augmented Hashin-Shtrikman method, however, includes nonlinear elasticity and the shear modulus of the matrix material. It therefore provides accurate estimates of the homogenized material when SAMM elements display negative stiffness and enhanced acoustical nonlinearity. The distortion of an acoustic wave propagating through the effective medium is studied through numerical solution of a nonlinear evolution equation that includes both quadratic and cubic nonlinearity. Finally, the forced nonlinear dynamic response of both a single SAMM element in a matrix and a domain of effective medium material embedded in matrix is considered. This behavior is of interest for generating enhanced absorption of acoustic wave energy because snapping leads to large hysteresis in the stress-strain response. A generalized Rayleigh-Plesset analysis is adapted to model the large-deformation dynamics associated with the system. / text

No description available.

No description available.

No description available.

No description available.

No description available.