Constrained-Membrane Acoustic Metamaterial Stability
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Solution Overview
Problem
Conventional acoustic metamaterials face issues such as instability, increased complexity in assembly, shorter effective working time due to vibration-induced pretension release, and poorer soundproofing performance due to total transmission phenomena, especially in low frequencies.
Innovation Solution
The development of constrained-membrane acoustic metamaterials (CAMs) that use constraint sticks to suppress undesirable vibration modes and create modes for total reflection at low frequencies, broadening the effective bandwidth for sound insulation, and combining CAMs with conventional materials to enhance sound transmission loss performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a rigid mass is placed in each unit cell to form an oscillation system with the membrane, then the operating frequencies can be tuned by adjusting the resonant frequencies of the mass-membrane system, but the mass detaches easily from the membrane under strong vibration, reducing stability and reliability
Solution Approach 1:
The patent removes the rigid mass component from the unit cell structure, extracting the problematic element that causes detachment issues. The acoustic metamaterial function is achieved solely through the membrane's local vibration modes without requiring attached masses, thereby eliminating the stability problem while maintaining frequency tuning capability through membrane parameter adjustment.
Solution Approach 2:
Instead of attaching mass to the membrane to achieve resonant frequency control, the patent inverts the approach by using the membrane itself as the oscillating element. The membrane's vibration modes are exploited to create acoustic metamaterial effects, reversing the traditional mass-attached configuration to eliminate detachment issues.
2Adaptability or versatility
If multiple weights are placed into each unit cell to overcome narrow-band operating frequencies, then the operating frequency bandwidth is broadened, but the weight, thickness and structural complexity of the materials increase
Solution Approach 1:
The patent achieves frequency bandwidth extension by adjusting membrane parameters such as tension, density, and geometric configuration rather than adding multiple masses. By varying these parameters, the membrane can support multiple vibration modes across different frequency ranges, broadening the operational bandwidth without increasing structural complexity or weight.
3Adaptability or versatility
If the pretension force applied to the elastic membrane is varied to tune operating frequencies, then the frequencies can be adjusted, but the pretension releases slowly under long-time vibration, reducing effective working time
Solution Approach 1:
The membrane structure is designed to maintain its own pretension state through its elastic properties and geometric configuration. The system self-regulates the tension distribution during vibration, eliminating the need for external pretension adjustment mechanisms and ensuring sustained operation without gradual tension release over time.
4Object-affected harmful factors
If conventional acoustic metamaterials are used to achieve total reflection at specific frequencies, then sound waves are reflected at designed frequencies, but total transmission occurs inevitably after total reflection, resulting in poorer soundproofing performance
Solution Approach 1:
The patent employs a composite structure combining the membrane element with the unit cell framework to create a multi-functional system. This composite design enables simultaneous achievement of total reflection at operating frequencies and suppression of total transmission phenomena, improving overall soundproofing performance by leveraging the synergistic interaction between different structural components.
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
CAMs provide improved stability, simplified fabrication, and enhanced sound insulation performance with a wider operating frequency bandwidth and reduced areal density, outperforming traditional acoustic metamaterials in both stability and soundproofing efficiency.
Implementation Method 1
the whole plate can generate strongly and locally resonant vibration in every region due to the oscillation effects of the mass-membrane or mass-filler system excited by the incidence of sound waves
Implementation Method 2
Unit cells partition the whole plate into small, disconnected and relatively independent regions, and thus the whole plate can generate strongly and locally resonant vibration
Implementation Method 3
the constrained membrane of the CAM can suppress undesirable vibration modes corresponding to the total sound transmission phenomenon and, meanwhile, create vibration modes for the total reflection phenomenon at low frequencies
Implementation Method 4
the Incident sound waves are totally reflected
Implementation Method 5
effectively soundproofing performance in low frequencies
Data Source
AI summary
This invention provides an acoustic metamaterial unit cell, consisting of a frame, a constraint stick placed in the frame and a piece of membrane covering at least one surface of the frame. This invention also provides an acoustic metamaterial plate comprised of the provided unit cells and a composite structure of acoustic materials. Additionally, the invention provides a method to design the operating frequency bands by modifying the structure and material properties of the frame, the constraint stick and the membrane in the proposed acoustic metamaterial. The proposed structure shows a priority in fabrication, stability and service life.