Scientists project sound waves through a patterned plate known as an acoustic hologram, which is often 3D-printed and computer-designed. Other researchers are developing a technology known as acoustic holography to shape sound waves, in order to more precisely design the location and shape of the pressure zones in a medium. “Many groups have been translating ideas from optics to acoustics,” says Alù. Now, engineers are adapting the tools for manipulating sound waves instead. Over the last half-century, engineers have achieved unprecedented control over light, with inventions ranging from lasers to fiber optics to one-way mirrors to holograms. Consequently, both exhibit many parallel phenomena: Your voice echoing in a canyon, for example, is mathematically analogous to light bouncing off a mirror. These days, engineers have taken a fresh perspective on sound-in analogy with light. People began to use sound to map spaces, whether they were in the ocean or in a human body.
Military researchers developed sonar to find enemy submarines, which medical engineers later adapted to image fetuses during pregnancy. In the 20th century, people reconceived sound as an imaging tool. Early technologies, dating back centuries, largely revolved around music, from building better acoustics for theaters to designing tuning forks. Acoustics, or the science of sound, “is an old and very established field,” says physicist Andrea Alù of the City University of New York.
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