In 2010, researchers at the University of Illinois in Champaign demonstrated the first broadband acoustic cloaking device. Basically a doughnut of acoustic metamaterial, the device caused a steel cylinder and other small objects placed in the center to fade from the view of a sonar scan.
Besides the promise of attaining invisibility and other strange effects, this demonstration—although too small to be of practical use—has exploded the research interest in developing practical acoustic metamaterials. Since 2008, the U.S. Navy has awarded $2.5 million in Small Business Innovation Research grants to Acentech Inc., Physical Optics Corp., Weidlinger Associates Inc., CFD Research Corp., Triton Systems Inc., Sensormetrix, and Eclipse Energy Systems Inc., for the development of acoustic metamaterials.