Underwater detection by sound wave transmission, reflection, transmission and attenuation, or removal
The rubber products for the purpose of noise are collectively referred to as underwater acoustic rubber. Rubber as a polymer is widely used in this field due to its damping property.
In the military, water and underwater ships use underwater acoustic rubber to monitor and identify the location of enemy ships, or to conceal themselves. In economic construction, it is used to probe submarine deposits, especially oil and gas. In addition, it is used to determine the location of shipwrecks and salvage shipwrecks, and to track fish stocks during fishing operations.
Under the function of water acoustic rubber, it can be divided into noise reduction, anti-sound and sound transmission. Among them, anti-sound and sound-transparent rubber are used to locate enemy ships, which is called “active sonar.” That is, the party engaged in the war determines the orientation and movement of the enemy submarine by means of underwater acoustic rubber. In addition, underwater ships, such as submarines, can also use noise-reducing rubber to reduce their own underwater noise, to avoid the search and tracking of enemy anti-submarine ships and anti-submarine aircraft, thus preventing target exposure and shielding and protection. This is called “passive sonar.”
The manufacturing points of several underwater acoustic rubbers are briefly described below.
(1) Silencing rubber
The main material should be selected from the characteristic acoustic impedance (the product of the rubber density and the propagation speed of the acoustic wave in the rubber) matching (close to) the acoustic impedance of the propagation medium (water). The preferred host materials are butyl rubber and nitrile rubber. Some bubble-like fillers such as cork powder and mica powder can be added to the rubber compound to enhance the sound absorption effect.
(2) Soundproof rubber
It is mainly used for the sound-permeable window of the shroud and the transducer of the sonar. The suitable rubber types are natural rubber, neoprene, butyl rubber and urethane rubber. Their sound transmission coefficient can reach more than 90%. In addition to being used to detect submarines, sound-permeable rubber can also detect mines. It can be used to detect submarine oil and gas fields in civilian use. Performance requirements are high sensitivity to water, sound and signal transmission, ie no distortion. It is also required that the characteristic acoustic impedance of the rubber used matches the characteristic acoustic impedance of the water. Natural rubber, neoprene, butyl rubber and urethane rubber are preferred for the rubber used.
(3) Anti-sound rubber
Used to eliminate and reduce noise interference. The focus of the formulation design is that the characteristic acoustic impedance of the rubber and the characteristic acoustic impedance of the water are large, and the rubber is required to have a microporous structure. There is air in the micropores. When the air content is greater than 50%, the shear modulus decreases and the wave velocity decreases, which results in high reflectivity at the interface between the foam and water. When the reflection coefficient is greater than 80%, it is effective. Eliminate the flow of water and the noise emitted by the device itself.