Text: Movie, based on data from a laser interferometer, depicts a "hyperfocusing" of a sound wave using time-reversal acoustics, in which a device produces a reversed version of a sound wave and sends it back to its original location. Usually, a wave cannot be focused to a spot smaller than half of its wavelength. "Hyperfocusing" means to focus the sound wave to a size smaller than this traditional limit. In the above graphic and animation, the sharp peak is an ultrasound wave focused to 1/14 of its initial wavelength. The point at which the wave focuses acts as a "sink" which absorbs the energy of the sound wave. To achieve hyperfocusing, it is crucial to time-reverse all of the initial sound wave, including its "near field" components, the fields that exist within a wavelength around the source of the sound. Previous time-reversal devices did not emit this important component of the sound field. Without this component, the time-reversed wave does not focus very well (this is what happens in the animation below). http://www.aip.org/enews/physnews/2002/split/604-1.html

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