A nonlinearly processed array for enhanced azimuthal resolution

An array with both linear and nonlinear signal processing modes is described. Theoretical and experimental results obtained with operation in each mode are contrasted. It is found that there is little difference in the 3-dB beamwidth but that the 10-dB and 20-dB beamwidths are improved by the nonlinear processing to an appreciable degree. The nonlinear processing results in a scanning beam, which is essentially collimated from ranges of 6 to 16 inches with a 20-dB beamwidth of 0.06 inch using a nominal frequency of 2.5 MHz. Since most medical scanning systems must use a wide dynamic range, the improvements of the 10-dB and 20-dB beamwidths represent a significant improvement of the azimuthal resolution capability.