Simple technique for beam steering of CW phased-array transducers

A system has been designed for automatically maintaining optimum insonation conditions during long-term monitoring of blood flow velocity. The transducer comprises two, one-dimensional, eight-element phased arrays, mounted side-by-side. Each transmit element is driven by its own carrier waveform, derived from the 50 MHz system clock. The phase relationship between the carriers is determined by pre-loading 4-bit binary counters, in order to direct the resulting ultrasound beam angle. Doppler signals from the receiving elements are processed to derive the appropriate control code, in order to close the loop, and enable a blood vessel to be tracked. The text describes the novel electronic process used for demodulating the Doppler signals, allowing each receive element to contribute equally in response to back-scatter from the chosen direction. This is achieved by pairing complementary drive and receive signals in eight demodulator stages.