The quasi-paraxial theory for phased arrays presented here can be used to estimate and analyze the acoustic field in the focal plane for a large scanning angle. The transient acoustic field is considered as the product of two terms that describe the time characteristics of the acoustic vibration over the array and the geometrical characteristics of the array, respectively. This method requires little computation time. The influence of special element shapes and functions that modulate the amplitude of the element vibration on the field distribution is also investigated.
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