Passive ultrasonic beamforming for fast and efficient imaging

This work explores the opportunity for utilizing ultrasonic arrays in a passive manner to increase imaging speed and accuracy, compared to conventional ultrasonic beamforming approaches. While conventional beamforming requires the use of many transmitters as well as receivers, the possibility exists to minimize the number of transmitters and exploit the normalized cross-power spectrum operator to extract "virtual" Impulse Response Functions between pairs of (only) receivers. In principle, this possibility would allow, for example, the use of a single transmitter element and processing the remaining elements as receivers (passively) to obtain similar image quality as using each element as both transmitter and receiver (as done, for example, in a Full Matrix Capture mode). By minimizing the number of transmitters, it would be possible to significantly increase imaging speed (ultrafast imaging) and simplify multiplexer hardware (few high-voltage output channels). The normalized cross-power spectrum could eliminate the distortion in the phase of the Impulse Response Functions which is commonly seen in active transmission modalities. These exciting possibilities are explored in the case of imaging defects in structural components.