Phase-aberration-correction algorithm for phased-array transducers using near-field signal redundancy

A near-field signal-redundancy algorithm for measuring phase-aberration profiles across an array has been proposed (Y. Li, 1997) and successfully tested (Y. Li et al., 1997) using a lineal array with relatively large element pitch (about 2.5 wavelengths). For a phased-array transducer. With element pitch about one half of a wavelength, similarities between common midpoint signals greatly increase. However. Use of small elements introduces the following problem: each element transmits signals into and receives echoes from a wide angular range, and these echoes may experience different phase-aberration values (ie: if the aberration is "non-isoplanatic"). In this case. The peak position of the cross-correlation function between common midpoint signals is only weakly related to the phase-aberration value at any particular direction. In this paper. A near-field, signal-redundancy algorithm for phased-arrays is proposed. The small elements are grouped into sub-arrays to obtain a narrow angular response and the similarity between common midpoint signals collected from sub-arrays remains high since dynamic near-field delay corrections are performed according to the positions of each of the transmitter and receiver elements in sub-arrays. Moreover. The sub-arrays can be steered to different directions in order to measure the phase-aberration values for each direction. Experimental results for an artificial, non-isoplanatic, aberrator are shown.