Nonlinear focal shift in focused ultrasonic transducers and its dependence on the Fresnel number

Yuri Makov, Victor Sánchez‐Morcillo, Francisco Camarena, Víctor Espinosa
2008 Journal of the Acoustical Society of America  
Acoustics 08 Paris A systematic study of the on-axis location of the maximum pressure and intensity points in the field radiated by a focused transducer is presented as well as the motion of these characteristic points as the transducer voltage is increased. Different initial distributions, ranging from uniform to Gaussian cases, are considered. Experimental and numerical results, based on the solutions of the KZK equation, with different initial conditions are analyzed. An analytical
more » ... of the initial (linear) shift of the maximum pressure position is given. This expression, and the results of the numerical simulations, shows a good agreement with the experimental data. As a main conclusion, we demonstrate that the axial range of the nonlinear shift of pressure is larger for strong initial focal shifts, occurring for small Fresnel number transducers. Theoretical and numerical predictions of the focal shift effect in Gaussian beams are also presented. In this work we have established the relation between the focal shift (both in linear and nonlinear regime) with the Fresnel number of the transducer.
doi:10.1121/1.2935674 fatcat:binodcqb4bdntkywajxzqf77ka