Sound waves travel just fine through Earth’s atmosphere, but once they strike water they’re much harder to hear. That’s because only about 1/1000 of sound energy makes it through the water-air boundary. Scientists have now developed a new material that can be placed on the water surface that significantly reduces that energy loss, allowing sound to be transmitted about 160 times more efficiently, the team will report later this month in Physical Review Letters. The researchers built a poker chip–size structure of latex rubber stretched over an aluminum frame coupled to a plastic ring containing a membrane. They designed the structure so that sound waves reflecting off its different parts canceled, meaning that more energy was directed toward the air-water interface. That’s the same principle behind antireflection coatings. The scientists tested their invention with sound waves within the range of human hearing and showed that sound levels dropped by about 6 decibels between air and water, compared with a drop of about 28 decibels without the structure. A conversation spoken on a boat, for instance, would sound pretty similar underwater with the new material in place, but it would sound like a hushed library whisper without it. If this material can be fabricated in bulk—and the researchers say there’s no reason it can’t be—simpler, less-sensitive underwater microphones can be used for land-sea communication for deep-ocean science or shipwreck exploration, for instance. This technology can also be adapted to medical ultrasonic imaging, the scientists suggest, boosting transmission of sound waves into the human body to yield clearer pictures of tissues and organs.
