"That is not a property that most materials have," Cummer said. "For instance, in air or water, sound speed is the same in all directions."
However, he said, it should be possible to engineer a composite material in which many different substances combined would have the desired overall characteristics.
The study appears in this month's edition of the journal Physical Review Letters.
The most obvious use of an acoustic cloak would be hiding submarines from enemy sonar—sound waves that are used to locate underwater objects.
But the advance could also be used in architecture—in music halls and theaters, for instance.
"Right now . . . the acoustics are built into whatever you're doing structurally," Cummer said. "So you probably have a set of tradeoffs, structurally and acoustically."
But with acoustic cloaking technology, "a giant beam that might be important structurally and bad acoustically could be rendered acoustically invisible."
The research carries importance far beyond the potential applications, said Xiang Zhang, a metamaterials engineer and physicist at the University of California, Berkeley, who was not involved in the study.
"It opens up important fundamental research on how you funnel light or sound waves into desired locations," he said.
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