Acoustics Seminar

Thursday 8 January 2015, ARL Conference Room #6 (A007), 2pm

Hello all!

Welcome back, and I hope you all had a safe and happy holiday. Dr. Hamilton would like me to pass on the following information regarding Kyle Spratt's seminar on Thursday, January 8th, 2015. The seminar will be held in Conference Room #6 at ARL at 2pm. The seminar is open to all and the information presented will be similar to his PhD dissertation. Abstract for the seminar is presented below. 

Harmonic Generation and Unique Focusing Effects in Shear Wave Beams in Tissue-like Media
Kyle Spratt

Recent research on the propagation of shear waves in tissue-like media has been motivated by the possibility of using such waves to image regions in the body characterized by an appreciable increase in the shear stiffness, such as breast cancer tissue. Soft biological tissue has a shear wave speed that is three orders of magnitude smaller than the compressional wave speed. It is thus amenable to finite shear strains that result in nonlinear material behavior. Shear wave propagation in such materials is modeled using a reduced constitutive equation which requires only three elastic constants to take into account nonlinear effects up to fourth order in the strain energy density. The nonlinear propagation of narrow-angle shear wave beams is investigated using a parabolic approximation due to Zabolotskaya (1986). A class of source polarizations is introduced which includes both the well-known case of linear polarization, as well as more complicated polarizations such as torsional and radial. Perturbation theory is used to derive an analytical solution for second-harmonic generation for the case of a beam with Gaussian amplitude shading, showing explicitly the relationship between the source polarization and the polarization of the subsequently generated second harmonic. Lastly we consider the unique focusing properties of radially-polarized beams, wherein strong focusing leads to a highly-localized region of longitudinal motion at the focus of the beam, the amplitude of which is comparable to the transverse motion. Possible uses of such beams for biomedical purposes are discussed.

Thank you,
--Ashley