Side-lobe suppression for ultrasonic imaging arrays

Equations describing the focal depth two-way continuous wave beam patterns of a linear array which is focussed on transmit and receive are analysed. By using different size apertures on transmit and receive, it is possible to place the minima of one beam pattern near the side-lobe of the other and achieve side-lobe suppression. The optimum side-lobe response occurs when the transmit aperture is ≈ 0.72 (or ) of the receive aperture. Simulations for pulsed mode operation of a 2 MHz synthetically focussed linear array, using this technique, are included. The implications for other imaging techniques such as confocal scanning acoustic and optical microscopy are discussed.