Non-paraxial multi-Gaussian beam model of Leaky Rayleigh waves generated by a focused immersion transducer

A non-paraxial multi-Gaussian beam (NMGB) model is proposed for Leaky Rayleigh Waves (LRWs) generated by a focused immersion transducer at oblique incidence. Using the NMGB model, the velocity fields are calculated and compared with the corresponding results obtained by the paraxial multi-Gaussian beam (MGB) model and the more exact Rayleigh-Sommerfeld integral (RSI) model. Numerical results show that the LRW beam behavior obtained using the NMGB model agrees well with that using the RSI model, but the NMGB model is much more efficient. Moreover the NMGB model overcomes the accuracy limitation of the MGB model. Good agreement between the NMGB model and experimental measurements for both on-axis and off-axis fields is obtained when an attenuation coefficient is introduced. In addition, this model can be used to measure the attenuation coefficient with consideration of the diffraction attenuation. It is observed that the attenuation coefficient of the LRW will increase when the acoustic impendence differences between the solid and fluid decrease. The NMGB model described in this article provides an efficient tool for calculating the velocity fields of the LRW and is therefore significant for practical applications of ultrasonic measurements.