Scientists use sound to see around corners

LONG BEACH, CALIFORNIA—Spies may soon have another tool to carry out their shadowy missions: a new device that uses sound to “see” around corners.

Previously, researchers developed gadgets that bounced light waves around corners to catch reflections and see things out of the line of sight. To see whether they could do something similar with sound, another group of scientists built a hardware prototype—a vertical pole adorned with off-the-shelf microphones and small car speakers.

The speakers emitted a series of chirps, which bounced off a nearby wall at an angle before hitting a hidden object on another wall—a poster board cutout of the letter H. Scientists then moved their rig bit by bit, each time making more chirps, which bounced back the way they came, into the microphones.

Using algorithms from seismic imaging, the system reconstructed a rough image of the letter H (above). The researchers also imaged a setup with the letters L and T and compared their acoustic results with an optical method. The optical method, which requires expensive equipment, failed to reproduce the more-distant L, and it took more than an hour, compared with just 4.5 minutes for the acoustic method. The researchers will present the work here Wednesday at the Computer Vision and Pattern Recognition conference.

The technique is years from practical application, but the authors suggest an ultrasound version might eventually be used on autonomous vehicles to detect unseen obstacles. Or it could be used to spy on your co-worker in the next cubicle.