As computers are becoming more powerful, researchers are extending the range of applications for acoustic imaging. Coherently sampling an array of sonic transducers creates a spatial filter that can map incoming sound waves based on their direction of arrival (DOA). A staple of acoustic array design is delay-and-sum (DAS) beamforming, whereby the microphone signals are delayed to bring signals from a desired direction into phase. Summing these delayed signals selectively amplifies waves coming from the desired direction, and repeating this steering process for a range of directions constructs an image of source intensity as a function of angle (Figure 1). DAS and other beamforming techniques were developed for radar and have been applied to seismic imaging, industrial testing, and quality control.

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