1. Current subs use 1-inch-thick rubber foam to reduce sonar detection. Materials scientists at Université Paris-Diderot, the University of Manitoba, and PSL Research University are working on a technique to create a much thinner sheet of rubber populated by thousands of bubbles that work to deflect sonar while saving on weight over the bulky foam. Lab tests have shown that the material cuts down on radar wave detection by 10,000 times.
In practice, a 4-millimeter film of bubble material could dampen a sonar signal by as much as 99 percent. A 0.16-inch-thick (4 millimeters) film with 0.08-inch (2 millimeters) bubbles could absorb more than 99 percent of the energy from sonar, cutting down reflected sound waves by more than 10,000-fold, or about 100 times better than was previously assumed possible.
In underwater experiments, the scientists bombarded a meta-screen placed on a slab of steel with ultrasonic frequencies of sound. They found that the meta-screen dissipated more than 91 percent of the incoming sound energy and reflected less than 3 percent of the sound energy. For comparison, the bare steel block reflected 88 percent of the sound energy.
There is the challenge of being able to economically produce durable bubble material to cover an entire submarine.
Physical Review B - Superabsorption of acoustic waves with bubble metascreens
2. Imagine a material that wicks sound across its surface like water droplets sliding over a windowpane. For submarines, such a coating would mean an entirely new way to slip past sonar without detection as sound waves pass harmlessly around the vessel.
Physicist Baile Zhang and his colleagues at Nanyang Technological University in Singapore think they may have found a way to design such a coating, which could work for any 3D shape—sharp corners included.
Sound waves like sonar hit his proposed coating, they strike an acoustically tuned material called a phononic crystal. That crystal bends the waves so that when they bounce off the hull, they loops around—smacking right back onto the surface to bounce over and over again. Zhang likens the process to a professional soccer player curving the ball.
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In practice, a 4-millimeter film of bubble material could dampen a sonar signal by as much as 99 percent. A 0.16-inch-thick (4 millimeters) film with 0.08-inch (2 millimeters) bubbles could absorb more than 99 percent of the energy from sonar, cutting down reflected sound waves by more than 10,000-fold, or about 100 times better than was previously assumed possible.
In underwater experiments, the scientists bombarded a meta-screen placed on a slab of steel with ultrasonic frequencies of sound. They found that the meta-screen dissipated more than 91 percent of the incoming sound energy and reflected less than 3 percent of the sound energy. For comparison, the bare steel block reflected 88 percent of the sound energy.
There is the challenge of being able to economically produce durable bubble material to cover an entire submarine.
Physical Review B - Superabsorption of acoustic waves with bubble metascreens
A bubble metascreen, i.e., a single layer of gas inclusions in a soft solid, can be modeled as an acoustic open resonator, whose behavior is well captured by a simple analytical expression. We show that by tuning the parameters of the metascreen, acoustic superabsorption can be achieved over a broad frequency range, which is confirmed by finite element simulations and experiments. Bubble metascreens can thus be used as ultrathin coatings for turning acoustic reflectors into perfect absorbers.
2. Imagine a material that wicks sound across its surface like water droplets sliding over a windowpane. For submarines, such a coating would mean an entirely new way to slip past sonar without detection as sound waves pass harmlessly around the vessel.
Physicist Baile Zhang and his colleagues at Nanyang Technological University in Singapore think they may have found a way to design such a coating, which could work for any 3D shape—sharp corners included.
Sound waves like sonar hit his proposed coating, they strike an acoustically tuned material called a phononic crystal. That crystal bends the waves so that when they bounce off the hull, they loops around—smacking right back onto the surface to bounce over and over again. Zhang likens the process to a professional soccer player curving the ball.
Read more »
