Beam patterns from pulsed ultrasonic transducers using linear systems theory

In medical ultrasonic imaging the beam pattern of the transducer is important in that it defines the lateral resolution of the system. Although the pulsed mode is generally used in diagnostic imaging due to its ability to provide increased axial resolution, the beam pattern is usually calculated assuming continuous wave (cw) excitation because of the simple Fourier transform relationship between the beam pattern and the aperture function for this case. Unfortunately, as the direction from the main lobe is increased, there is an increased disparity between the cw beam pattern and the pulsed beam pattern which has particular consequence when calculating the grating lobe response of an array. In this paper a method is presented using linear systems theory to analyze the beam patterns from an aperture with pulsed excitation. The frequency spectrum of the pulsed input signal is multiplied by the system transfer function and the beam pattern is obtained by an inverse Fourier transform. It is found that the syst...