Aperture apodization to reduce the off-axis intensity of the pulsed-mode directivity function of linear arrays

Abstract There is considerable interest in aperture apodization for enhancing image quality. With continuous wave excitation, the influence of apodization can quite easily be predicted: the directivity function in the far-field corresponds to the Fourier transform of the aperture function. We, however, analyse a practical situation — short acoustic pulse emission focused in the near-field. Nine types of aperture function (for example, Tukey, Parzen, Hamming) are compared. It appears that with the pulsed mode a considerable reduction in off-axis intensity can be obtained by judicious choice of the aperture function. Side-lobes can be completely eliminated. As a tool, an approximate relationship is established between the Fourier transform of the aperture function and the main-lobe width of the directivity function. Further, an optimum balance is sought between the main-lobe width and the width at the −25 dB level of the directivity function.