A three-dimensional transmission line matrix model for ultrasonic imaging

Abstract

ABSTRACT A three dimensional numerical model for elastic wave propagation in multilayered structures is the subject of this paper.The model is based on the T ransmission L ine M atrix method (TLM) and has a three dimensional acoustic node as a keyelement. A full description of the numerical method implementation is provided. The numerical analysis was applied tostructures with a relatively complicated geometry, similar to the geometries used in non-destructive testing and inmedical imaging. The comparison between the experimental and numerical frequency response for a multi-layeredcylindrical piece validates the proposed numerical model. An acoustic impedance profile similar to biological tissuewas numerically modeled. The comparison between real and numerically generated signals shows good agreementbetween experiment and numerical analysis.Key words : Transmission line matrix (TLM) , ultrasonic imaging , array transducers, time domain modeling 1. INTRODUCTION The main purpose of this article is to demonstrate how a TLM model can be developed and numerically implemented tosimulate the complex process related to ultrasonic propagation. The significant advantages of this method are flexibilityin dealing with various types of sources and with almost any kind of acoustic impedance profiles. This method is notthe only method used for the numerical modeling of elastic wave propagation. Before pointing out the main cornerstones of the TLM method, a brief review of the other methods used in acoustic imaging is necessary. One of the firstnumerical methods proposed was the ray tracing method. This method is considered an alternative method to solve thewave equation. In this approximation geometrical optics can be applied successfully. The theoretical support forapplying this method in ultrasonic nondestructive testing was first summarized by Achenbach