Nearfield of ultrasonic transducer-lens systems: Theory with Gaussian-Laguerre formulation

Within the regions of validity of the Fresnel approximations, a Gaussian-Laguerre formulation permits rapid calculation of fields of transducer-lens systems. Separation of lens from the transducer is found to change significantly the structure of field. When the lens is at a focal length from the transducer, the field is found to be symmetric with respect to the focal plane. The asymmetry when the lens is not at this distance depends on the location of the lens and the ratio of the focal length to the length of the nearfield.