Just is in at this moment, the mobile phone of cummer rang.

恰恰就在这时，女友的手机响了。

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“Ten years ago we wouldn’t know how to make one,” said Steve Cummer, associate professor of electrical and computer engineering at Duke University Cummer.

“十年以前，我们不知道如何制造出一个这样的东西。” 杜克大学电子与计算机工程学院副教授，史蒂夫•卡莫如是说。

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“Ten years ago we wouldn’t know how to make one, ” said Steve Cummer, associate professor of electrical and computer engineering at Duke University Cummer.

“十年以前，我们不知道如何制造出一个这样的东西。” 杜克大学电子与计算机工程学院副教授，史蒂夫•卡莫如是说。

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"Fundamentally, in terms of hiding objects, it's the same - how anything is sensed is with some kind of wave and you either hear or see the effect of it, " said Steven Cummer of Duke University.

BBC: Acoustic 'cloaking device' shields objects from sound

Now, Dr Cummer and his colleagues have shown off an acoustic cloaking technique that works in air, for audible frequencies between one and four kilohertz - corresponding to two octaves on the higher half of a piano.

BBC: Acoustic 'cloaking device' shields objects from sound

"How the sound reflects off this reflecting surface with this composite object on it - which is pretty big and has a cloaking shell on it - really reflects... just like a flat surface does, " Dr Cummer said.

BBC: Acoustic 'cloaking device' shields objects from sound