Ultrasound Phased Array Delay Lines Based on Quadrature Sampling Techniques

Abstract

Two signal processing techniques are presented for applica- tion to ultrasonic phased array delay line systems. By using bandwidth considerations, it is shown that the signals may be either mixed to a lower frequency range or sampled at a rate commensurate with the signal bandwidth, rather than the highest frequency component, prior to delay. Both techniques lower the bandwidth requirements of the delay lines and neither require reconstructing a delayed version of the original radio frequency (W) waveform. The latter approach requires no mixers, however, as samples of the in-phase and quadrature compo- nents are obtained directly from the RF signal. The required focused signal is produced by delaying and summing the samples. It is shown that RF signals with 60 percent fractional bandwidth may be processed in this way by sampling in quadrature at only 5 of the center fre- quency. (Quadrature sampling requires that two samples be taken 90' apart with respect to the center frequency every sampling interval.) This was implemented in a four-element 5-MHz annular array system, and the results, including beam plots and tissue scans, are shown.