Efficient transmit beamforming in pulse-echo ultrasonic imaging

A high performance ultrasound imaging system requires accurate control of t he amplitude of the array elements, as well as of the time delays between t hem, both in the transmit and receive modes. In transmission, conventional array aperture windowing implies a different driving voltage for each eleme nt of the array, an expensive solution for systems with a large number of c hannels. In this paper, we present a simple, versatile, and inexpensive bea mforming method that operates the aperture windowing in the transmit mode, simply controlling the lengths of the electric pulses driving the array ele ments. Computer simulations and experimental measurements are presented for different types of arrays. They confirm that the proposed beamforming tech nique improves the contrast resolution of the imaging system, reducing the off-axis intensity of the radiated field pattern. Moreover, the axial resol ution is slightly enhanced, because the overall length of the transmitted u ltrasonic pulse is reduced.