3aSP9. Compensation for array nonidealities by electronics.

Session: Wednesday Morning, June 18

Author: D.-L. (Donald) Liu
Location: Dept. of Elec. Eng., Univ. of Rochester, Rochester, NY 14627
Author: Robert C. Waag
Location: Dept. of Elec. Eng., Univ. of Rochester, Rochester, NY 14627
Author: Clyde Oakley
Location: Tetrad Corp., Englewood, CO 80111


Array elements usually have nonuniform characteristics in terms of element position, sensitivity, and waveform shape. Crosstalk caused by acoustic and electrical coupling limits the directivity of individual elements. These array nonidealities can be compensated by using pulser electronics with programmable transmit waveforms. Experiments were performed with a 2048-element ring transducer and a 3x3 test block for a 64x64-element 2-D array. With the ring transducer, a thin wire was suspended at the center of the ring, and single-element, pulse--echo data were collected for each element. To derive the one-way inverse response for each element, the two-way response was deconvolved using FFT, with special attention to phase unwrapping. Implementation of the inverse filtering reduced element arrival time fluctuation from 47 to 0.9 ns, energy level fluctuation from 1.2 to 0.4 dB, and increased the waveform similarity from 0.94 to 0.99. With the 3x3 test block, cancellation of crosstalk was performed by exciting neighboring elements with an opposing signal. The opposing signal was obtained by multiplying the original signal with a decoupling coefficient. Experimental results show that, with the particular test block, a decoupling coefficient of -0.08 extended the -6 dB half-angle from 10.8 to 14.8 deg, with a corresponding decrease of 4.5 dB in sensitivity.

ASA 133rd meeting - Penn State, June 1997