Underwater sub-wavelength local resonance type acoustic metamaterial

Abstract

The invention discloses an underwater sub-wavelength local resonance type acoustic metamaterial which comprises a water area 1, a stainless steel cylindrical shell 2 and a stainless steel three-fork star-shaped cylinder 3. Included angles among three outer forks of the stainless steel three-fork star-shaped cylinder 3 are 120 degrees, and an inner cavity of the cylinder is evenly divided into three fan-shaped cavities 9, 10 and 11. The three fan-shaped cavities 9, 10 and 11 are air domains. The underwater sub-wavelength local resonance type acoustic metamaterial disclosed by the invention hasfour sections of extremely wide complete band gaps in a frequency band [0Hz, 60000Hz]. In a complete band gap, propagation of sound waves is completely cut off and cannot continue to propagate forwards, and the possibility that an underwater object is detected by sonar due to radiation noise of the underwater object is reduced. The underwater sub-wavelength local resonance type acoustic metamaterial is provided with a Dirac point, and the standardized frequency of the lowest-frequency Dirac point is 0.0072 and is far lower than 1. The sound waves near the Dirac point frequency can realize zero-phase-difference propagation without changing the wavefront formation of the sound waves, and the possibility that underwater obstacles are actively detected by sonar is reduced.

Description

technical field [0001] The invention relates to a local resonance structure, a Dirac point, a sub-wavelength band gap, an acoustic metamaterial, acoustic stealth and acoustic shielding, and in particular to an underwater sub-wavelength local resonance type acoustic metamaterial. Background technique [0002] Compared with air, the propagation speed of sound waves in water is faster, about 1500m / s. Therefore, the wavelength of sound waves in water at the same frequency is more than four times the wavelength of sound waves in air. The wavelength corresponding to the lowest bandgap center frequency of traditional Bragg scattering phononic crystals is about twice the lattice constant, that is, traditional Bragg scattering phononic crystals can block sound waves with a wavelength about 1 / 2 times the lattice constant spread. Therefore, in order to realize the shielding of underwater low-frequency noise and acoustic stealth, a larger lattice constant is required. A larger lattic...

AI Technical Summary

Problems solved by technology

Taking the acoustic stealth of important national defense equipment such as submarines as an example, the noise emitted by the submarine engine becomes the main sound source of passive detection by sonar, and the shielding of the low-frequency noise of the engine requires the use of thicker sound-absorbing materials, which are expensive and will seriously limit the ability of submarines. Optimizing the overall performance of the body

In addition, the rapid development of active sonar technology has seriously improved the detectability of submarines and reduced the stealth performance of submarines

Since the impedance of water is relatively close to the impedance of materials, structures such as Helmholtz resonators commonly used in air are difficult to apply to sub-wavelength acoustic shielding underwater

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