Asymptotic evaluation of the pulse train radiated by an angled beam and fluid coupled rectangular ultrasonic transducer

The near field underneath the ultrasonic probe fluid coupled to an isotropic solid is approximated in the frequency domain by a closed form asymptotic solution. The approximation is based on the problem decomposition and uses the stationary phase method evaluating the response to an equivalent surface source. This results in a sum of contributions, each dominating in a specific geometrical region, the main beam or a side lobe. The transitional zones are also described. The pulse trains are computed using the harmonic synthesis and compared with the results obtained by direct calculation of Fourier integrals. It is shown that the asymptotic approach permits us to elucidate the physics of problem and leads to a numerical algorithm which is about 104 times faster than the direct computations. (C) 2010 Acoustical Society of America. [DOI: 10.1121/1.3292997]