Only one percent of sound occurring underwater can be transmitted to the air. This may change due to a new device designed by scientific researchers. The device is constructed of a new metamaterial that has capabilities standard metals do not. The new material can increase the transmission of sound by thirty percent. According to the Yonsei University in Seoul, South Korea, and the Hokkaido University in Sapporo, Japan, it is possible this new device can be used in the future to listen to sonar and marine life.
Hydrophones are currently used for the detection of sounds occurring underwater, but the device must be underwater in order to work. The new device floats above the surface of the water in a small cylinder. It is constructed using a weighted rubber membrane, and a metal frame. When the device is hit with sound waves originating underwater, the device vibrates causing tuned frequencies to be heard above the water. This device is called the Noisemaker. For additional details on this device, please visit https://www.sciencenews.org/article/new-device-can-transmit-underwater-sound-air.
According to Oliver Wright of the Hokkaido University, 100 percent of sound is reflected by a hard surface. He believes this can be mitigated with an intermediary structure. Air and water are both resistant to sound, and this is called acoustic impedance. Due to the density of water, the acoustic impedance exceeds air by 3,600 times. When a layer of material is added in the right thickness, the amount of reflection in the incoming wavelength is reduced. This is how the anti-reflective coating used for glasses and camera lenses works.
According to Oleg Godin, one of the physicists in Monterey, California at the Naval Postgraduate School, the new device is a tour de force. One of the most complicated issues the researchers will have to overcome is the device is unable to transmit sound when it comes in contact with the angles surface. The device is being tested inside of a tube while in the laboratory, and this environment only has one direction. When the device is on the vastness of an ocean or a lake, the sounds transmitted would be limited to a small area directly underneath the device.
The other major issue is there is a limitation to the metamaterial, and only a narrow band of frequencies can be transmitted. Any noise occurring outside of the devices range will register as usual against the surface of the water. The scientists still remain optimistic regarding taking the next steps.