Nonlinear Acoustics in Underwater and Biomedical Applications: Array Performance Degradation and Time Reversal Invariance.
Abstract
This dissertation describes a model for acoustic propagation in inhomogeneous fluid media and explores the focusing by arrays onto targets under various conditions. The work explores the use of arrays for acoustic and biomedical applications. Aspects of propagation and phasing that can lead to reduced focusing effectiveness are described. Among the most important debilitating effects studied here are medium absorption, medium nonlinearity, and imperfect initial phasing of the signals at the array elements. Acoustic wave propagation in fluid media is modeled by obtaining a wave equation from the basic equations of fluid mechanics, and from some description of the propagating environment and its boundaries. This study uses analysis and numerical simulations to study the behavior of the acoustic focusing systems described. The finite-difference time-domain method is used to solve the wave equation for some applications, and the strengths and weaknesses of this method are discussed. Beyond modeling and simulating the propagation and focusing of acoustic fields, this dissertation looks at the heating effects of ultrasound in an absorbing thermoviscous fluid. The application considered is the deposition of ultrasonic energy onto target tissue regions for the purpose of effecting therapeutic heating for hyperthermia.
Document Details
- Document Type
- Technical Report
- Publication Date
- May 21, 1999
- Accession Number
- ADA369813
Entities
People
- Ibrahim M. Hallaj
Organizations
- University of Washington