Use of a transient wave propagation code for 3D simulation of cw radiated transducer fields

In order to compute continuous wave (cw) ultrasonic wave fields in complex media, where analytical approaches are extremely difficult, numerical simul ations on large computational grids must be employed. The use of a time dom ain code, normally used for transient wave propagation in heterogeneous med ia, is used here as a tool to simulate continuous wave fields. As a startin g point, the case of the three-dimensional pressure field radiated from a c ircular aperture in water is computed. These numerical simulations are perf ormed on a massively parallel computer and compared with experiment and kno wn theory. The computations are performed on very large three-dimensional g rids that span the near to the far field. As a trial case, a numerical comp utation of the radiated field from a continuous-wave excited transducer in a baffle is compared with an analytical evaluation using the Rayleigh surfa ce integral and experiment. In addition, results are presented that show th e effect of a small defect placed in the beam. To do this, a small cylindri cal copper scatterer was placed in the near field, in both the computation and an accompanying experiment. These cases are done in preparation for usi ng the same approach for computing cw fields radiated from a transducer int o complex heterogeneous media. (C) 1999 Elsevier Science B.V. All rights re served.