Thinner Stealth Coatings

To avoid detection by sonar, submarines are often covered with sound-absorbing, perforated rubber tiles called anechoic coatings. The tiles in use today are a few centimeters thick, but the same degree of stealth protection could perhaps be provided by a much thinner coating, according to researchers in Canada and France. They predicted that a few millimeters of soft material containing regularly spaced air pockets can absorb well over 99% of the acoustic-wave energy impinging on it.