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By Jesse Bang
Perhaps if we can outfit submarine hulls with two layers instead of one, we might be able to cancel out the reflected waves. I have already measured out how thick the gap between the hulls should be: x(lambda)/4; where x is any odd integer. In this way, we will recieve reflection where the waves have the least energy, which is at the equilibrium.

The first layer should be any kind of material able to transmit 66% of wave energy and reflect 33%. 66% of the wave energy is transferred into the gap between the hulls, where it is then reflected yet again through the first layer. This accounts for 66% of 66% of the initial wave energy. since it most nearly matches that of the originally reflected 33%, and since the spacing is correct so that dephasing might occur, most of the waves will be cancelled, creating a much, much weaker sonar signal. It might be small enough to even avoid detection by sonar systems aboard submarines. If no such material is available, perhaps ordinary steel with holes would work.

Of course there is the significant problem of not knowing the wavelengths of the many thousands of sonar devices on submarines throughout the world.

Reward: the navy's recognition of a feasible technology
By mikem
Sounds like it would work. I think it is actually passive sonar cancellation though. Active cancellation would refer to an electronic version where the sonar pulse is inverted and retransmitted electronically. The military does this for radar, so perhaps it is done for sonar too. (It's cheaper than two hulls as well!)
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