That means that an object under the stack - in the team's experiments, a block of wood about 10cm long - would not "hear" the sound, and any attempts to locate the object using sound waves would not find it.

BBC: Acoustic 'cloaking device' shields objects from sound

At Wi Spa (www.wispausa.com), a 24-hour, Korean-style, three-story, 48, 000-square-foot haven, you can even spend the night - provided you sleep on the bamboo mats and wood block pillows in the Jimjilbang, or common area, located on the lower level.

BBC: Ethnic Los Angeles

Today it's Plaid Cymru - a party with the newest leader on the block in Leanne Wood, and the party that's done the most thinking about its future over the past year.

BBC: State of Play 2 - Plaid Cymru