Ultrasparse ultrasonic synthetic aperture beamforming via passive sensing

This presentation will describe the implementation of a passive ultrasonic sensing technique to achieve ultrasparse-transmission Synthetic Aperture Focusing (SAF) with Full Matrix Capture (FMC) capabilities. SAF ultrasonic arrays with sparse transmissions have been employed in both medical and industrial NDT imaging to increase imaging speed and simplify multiplexer hardware by reducing the number of high-voltage output channels, at the expense of a reduced beamforming matrix. A technique based on passive reconstruction of the ultrasonic Impulse Response Function (IRF) between two receivers will be demonstrated to create a “virtual” FMC capture while keeping a minimum number of physical transmitters, hence an ultrasparse-transmit array with full synthetic focusing capabilities. Several key steps of this passive beamforming approach will be discussed from both a theoretical and an experimental standpoint. The technique will be demonstrated for the imaging of drilled holes in an aluminum block using a linear, 64-element transducer array and only 1–4 physical transmitters. While the results presented have direct application to NDT imaging of solids, many of the aspects can be potentially applied to ultrafast imaging in the medical field, as well as to seismic interferometry for the health monitoring of civil structures.