Shung, “Design of an analog beamformer for very high-frequency ultrasound transducer arrays

A beamformer is described that is used to process the data from a high frequency linear array with frequencies up to 75MHz. This unit is one part of a test system, which has the capability to characterize ultrasound transducer arrays up to 128 elements. This beamformer consists of three stages: delay unit, delay switches and summing unit. They have the following characteristics: the delay and summing units are realized in the analog domain, utilizing 4-zone dynamic focusing, and dynamic aperture switching with very wide bandwidth. The delay unit consists of a set of fixed delays with Sns resolution, and a set of adjustable delay lines with a resolution of 1 ns. A set of 4: 1 multiplexers is used to switch the different delays for different focusing zones. In our system, the focal range is divided into 4 zones consisting of a near, middle, far and fourth zone with a different set of delays for each zone. Dynamic aperture switching is accomplished by sequential selection of the multiplexer network. The aperture is set according to the focusing zone. For near zone, middle zone, far zone and fourth zone focusing, apertures are set to 8,12, 1 6 and 16 elements respectively. In the last stage, very wide band summing amplifiers are used with surface mount resistor networks to decrease phase errors. Test signals have been generated. The multiplexing system and delay lines have been characterized. The beamformer lateral and axial resolution have been characterized by a simulated phantom utilizing the FIELD program. The future work is to interface the beamforming architecture with a high frequency array