Sound Generators Targeting Smartphone Mics Could Help Find Disaster Victims

University of Tokyo student Shogo Takada has been working on a way to locate disaster victims buried under rubble — by playing sounds their smartphones can pick up.

"This method is effective for locating victims buried under debris or soil caused by earthquakes or landslides because sound waves can propagate through them," explains Takada of the search-and-rescue system he is developing. "It could also be used to locate rescuers affected by secondary disasters."

Designed to help locate victims buried out-of-sight and who may not be able to call for help themselves, Takeda's system is designed to tie in to the ubiquitous smartphone. A rescue team deploys one of two sound-generating devices — one designed around a monopole system that radiates its sound on all sides and the other a directional dipole system that only radiates sound front and back — the output of which is then picked up by the user's smartphone.

The smartphone, in response, triggers its own signal, an electromagnetic wave that can be picked up by the rescuers and used to estimate the victim's location — accurate, field-testing has proven, to a 5.04 degree error over a 10 square meter (around 108 square feet) search area.

"One limitation is that the method assumes the victim should possess a device equipped with a microphone," Takada admits. "This is a more restrictive condition compared to traditional techniques that detect sounds or voices emitted by the victim. In future work, we plan to develop a method that can estimate not only the azimuth angle but also the elevation angle of the sound source. Additionally, we aim to expand the system to use two sound sources to achieve three-dimensional localization."

Takeda is due to present his findings in Honolulu today at the Sixth Joint Meeting of the Acoustical Society of America and Acoustical Society of Japan.