Difference frequency pressure within the interaction region of a parametric array

A theoretical model that predicts difference frequency pressure within the interaction region of a parametric array is presented. Linear and nonlinear attenuation are neglected, and it is assumed that the primary signals are spherically spreading throughout the interaction region. It is shown that with these assumptions the three-dimensional scattering integral can be reduced to a single integral if the primary pressure fields are axially symmetric. Analyses of the error introduced by assuming the primary fields are spherically spreading and by neglecting linear attenuation are presented. Theoretical results compare favorably to p’revious experimental results. The results indicate that diffraction effects are more important than attenuation when the observation point is within the interaction region and when primary signal level reduction is due more to spherical spreading than attenuation. Subject Classification: 25.35; 20.30, 20.15.