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A polystyrene bead (3mm diameter) is trapped inside an invisible acoustic hologram generated from a flat array of miniature loudspeakers (40Khz), in this undated handout photo courtesy of Asier Marzo, Bruce Drinkwater and Sriram Subramanian. Researchers on October 27, 2015, said they have developed a tractor beam that uses high-amplitude sound waves inaudible to humans to levitate, move and rotate small objects without making contact with them. They envisioned practical uses for the device including medical applications that would not require incisions. (Photo by Asier Marzo, Bruce Drinkwater and Sriram Subramanian/Reuters)
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