Finite amplitude near-field modelling of ultrasonic fields using a transfer matrix formulation
In modern ultrasonic equipment as used in medical diagnostics (and particuarly for lithotripters), the nonlinear effects play an important role. In a number of devices, they considerably affect the measured characteristics of the ultrasonic field and are therefore worth studying in detail. In its present form, the method models the propagation of steady state ultrasonic fields in a thermoviscous fluid. The acoustic field is propagated along the axis of symmetry with substeps that acount for diffraction, attenuation, and nonlinearity. The diffraction substep involves the use of the Helmoltz-Huyghens integral for the pressure applied to equally spaced planes which are perpendicular to the axis of symmetry. Implementation of this integral for two arbitrary consecutive reference planes leads to a transfer matrix size which does not depend on the specific problem. The nonlinear and attenuation substeps are based on the frequency domain solution of the Burgers equation. The method is tested by comparion with exact solutions in the two limiting cases of linear diffraction and nonlinear plane wave propagation. A comparison with measurements performed on the nonlinear field of a focussed 1.0 MHz source is given.
Bibliographic Reference: Report: PTB-MA-42 EN (1995) 64pp.
Availability: Available from Physikalisch Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig (DE)
Record Number: 199610062 / Last updated on: 1996-02-16
Original language: en
Available languages: en