Membrane-type acoustic metamaterial with negative dynamic mass.

Area of Science:

• Acoustics
• Materials Science
• Metamaterials

Background:

• Traditional sound attenuation often follows the mass density law, limiting effectiveness at low frequencies.
• Developing materials that overcome this law is crucial for advanced acoustic applications.
• Membrane-based structures offer potential for novel acoustic properties.

Purpose of the Study:

• To experimentally realize and theoretically understand a novel membrane-type acoustic metamaterial.
• To demonstrate its capability to significantly break the mass density law for sound attenuation.
• To explore the underlying physical mechanisms, including negative dynamic mass.

Main Methods:

• Experimental fabrication of a simple membrane-type acoustic metamaterial.
• Utilizing low-frequency oscillation patterns in an elastic film with fixed boundaries.
• Employing vibrational eigenfrequency tuning by adding a central mass.
• Conducting finite element simulations to analyze displacement and dynamic mass.
• Comparing experimental results with theoretical predictions.

Main Results:

• Achieved sound attenuation approximately 200 times greater than predicted by the mass density law in the 100-1000 Hz range.
• Observed low-frequency oscillation patterns due to weak elastic moduli of the membrane.
• Demonstrated near-total reflection at a specific frequency between two eigenmodes.
• Explicitly showed negative dynamic mass around the total reflection frequency via simulations.

Conclusions:

• The developed membrane-type acoustic metamaterial offers a simple yet highly effective method for low-frequency sound attenuation.
• The study validates the concept of breaking the mass density law using membrane dynamics and negative dynamic mass.
• Excellent agreement between experimental findings and theoretical models confirms the understanding of the material's behavior.