Thin-Layer Metamaterial for Low-Frequency Underwater Sound Insulation
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Solution Overview
Problem
Existing underwater sound insulation materials are ineffective in blocking low-frequency acoustic waves (200-2,000 Hz), limiting their application in acoustic stealth technology for underwater equipment.
Innovation Solution
A thin-layer low-frequency underwater sound insulation metamaterial is designed using a quasi-static impedance mismatch mechanism and density-based topology optimization, comprising two cover plates and a sound insulation layer with hollow rectangular column structures and connecting units, achieving a negative Poisson's ratio and improved sound insulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional sound insulation materials are used, then high-frequency sound insulation is effective, but low-frequency sound insulation performance is insufficient
Solution Approach 1:
The patent changes the physical parameters of the sound insulation material by introducing a periodic microstructure with specific geometric parameters (unit cell dimensions, wall thickness, porosity). This transforms the material from a conventional homogeneous structure to a metamaterial with tailored acoustic impedance characteristics that enable effective low-frequency sound insulation through impedance mismatch mechanisms.
Solution Approach 2:
The patent creates a composite metamaterial structure combining solid walls and air cavities in a periodic arrangement. This composite design integrates multiple functional elements (sound reflection from solid walls, absorption from air cavities, impedance mismatch from periodic structure) into a single material system that achieves broadband sound insulation across low and high frequencies.
2Reliability
If sound insulation material thickness is increased to improve low-frequency performance, then sound insulation effectiveness increases, but device weight and volume increase
Solution Approach 1:
The patent employs a thin-layer periodic structure with optimized wall thickness that functions as an acoustically effective barrier despite its minimal physical thickness. The periodic microstructure concentrates acoustic energy interaction within a thin profile, achieving low-frequency sound insulation without requiring thick material layers, thereby maintaining lightweight characteristics.
Solution Approach 2:
The patent transforms the sound insulation mechanism from thickness-dependent to parameter-dependent by optimizing the geometric parameters of the periodic microstructure (unit cell size, wall thickness ratio, porosity). This allows thin layers to achieve effective low-frequency insulation through carefully tuned structural parameters rather than relying on material thickness.
3Reliability
If dense solid material is used for sound insulation, then sound blocking capability improves, but material density and weight increase
Solution Approach 1:
The patent utilizes a periodic structure with intentional air cavities and porosity that creates acoustic impedance mismatch. The porous design with controlled void spaces enables effective sound wave reflection and absorption through impedance discontinuities, achieving sound insulation performance without requiring dense solid material, thereby reducing overall material quantity and weight.
Solution Approach 2:
The patent creates a composite structure combining solid walls with air cavities in a periodic arrangement. This composite design leverages the acoustic properties of both solid materials (reflection) and air spaces (absorption, impedance mismatch), achieving effective sound insulation with reduced material density compared to solid homogeneous materials of equivalent thickness.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The metamaterial provides excellent sound insulation performance in the 200-2,000 Hz frequency range with an average of 20 dB reduction, maintaining a lightweight and mechanically robust structure with an overall density less than 350 kg/m3.
Implementation Method 1
based on the quasi-static impedance mismatch mechanism and the density-based topology optimization method
Implementation Method 2
Damping dissipation sound insulation: The energy of the equipment radiating acoustic waves to the outside is reduced by means of the vibration damping dissipation inside the material or the absorption of scattered acoustic waves
Data Source
AI summary
The present disclosure provides a thin-layer low-frequency underwater sound insulation metamaterial, including two cover plates and a sound insulation layer. The sound insulation layer is composed of sound insulation components arranged in an array periodically. The sound insulation components each include a sound insulation unit and four connecting units. The sound insulation unit is of a hollow rectangular column structure. The four connecting units are arranged at four corners of the sound insulation unit. Every two adjacent sound insulation units are connected through the connecting units. A long side wall of the sound insulation unit and the corresponding cover plate have an included angle of 0-90°. The metamaterial can obtain a smaller equivalent acoustic impedance in propagation direction of acoustic waves, and compared with a sound insulation material of a square honeycomb structure with the same thickness, the metamaterial has greatly improved sound insulation performance.