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Dinner tables and windows can now be turned into speakers, thanks to a mobile-phone-sized device called a Soundbug. It sticks to any flat surface via a suction cup, and contains an 8-millimetre rod of Terfenol, a mix of terbium, iron and dysprosium that expands and contracts in a varying magnetic field. The rod is fixed inside a wire coil. When signals from a hi-fi travel through the coil, they produce a rapidly alternating magnetic field that makes the Terfenol rod shrink and expand. The resulting vibration forces the whole surface to pump out sound, says maker Newland Scientific, of Hull.…