Fig. 1.
(a) The transmit event focused at point Fn is referenced in time to the beam origin On, the last point on the array to transmit the wave. The focused wavefront (dashed line) is made up of individual spherically diverging waves including from transmit element T (solid line). (b) The time is calculated at which the wave was emitted from the transmit element T for transmit event n (in this case prior to On). (c) The superposition of the transmit fields from multiple elements forms an effective point source at T where their profiles intersect. (d) Propagation of the individual focused beams away from T form an effective diverging wavefront (solid line) that intersects the point to be imaged P. The other components of the individual focused beams (dashed lines) remain as background components of the transmit pressure field.