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Purpose <p>Low-frequency noise (LFN) generated by mechanical machines, particularly below 500&#xa0;Hz, is difficult to mitigate using conventional materials, and prolonged exposure can be harmful to humans. Acoustic metamaterials (AMMs)-based enclosures developed so far typically provide only narrow-band attenuation in this range and face challenges in large-scale implementation. To address these limitations, the present work introduces a simplified enclosure for broadband LFN control from a vacuum pump. The design employs a unit cell comprising a thin elastic synthetic rubber membrane backed by four parallel U-shaped cavities of varying depth, providing effective attenuation without complex geometries or added mass on the membrane, while ensuring scalability for real-world applications.</p> Materials and Methods <p>A subwavelength hybrid membrane-type acoustic metamaterial (MAM) was designed and fabricated for broadband LFN attenuation. The unit cell, MU4-AM, comprises a thin synthetic rubber membrane backed by four parallel U-shaped cavities, enhancing thermo-viscous losses and sound absorption (SA). A finite element analysis (FEA)-based parametric study optimized the membrane thickness to maximize normal-incidence SA in the pump’s dominant noise range. The unit cell was fabricated using polylactic acid (PLA) filament with a synthetic rubber membrane, and its acoustic performance was validated in an impedance tube through sound absorption coefficient (SAC) and sound transmission loss (STL) measurements. A full enclosure assembled from MU4-AM cells was further tested for insertion loss (IL) in an anechoic chamber.</p> Results <p>The MAM enclosure demonstrated an average IL of 12.2 dB in the 200–600&#xa0;Hz range. The directivity patterns in both the vertical and horizontal planes exhibited approximately uniform noise attenuation across the microphone angular positions.</p> Conclusions <p>The MAM-based enclosure provides a scalable and efficient solution for suppressing noise from a vacuum pump. Its broadband low-frequency performance, combined with a compact and modular design, makes it well-suited for deployment in mechanical rooms, laboratory spaces, and other critical interior environments within buildings. This simplified yet effective approach highlights the potential of MAMs for real-world noise control applications without relying on complex internal structures.</p>

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Membrane-Based Acoustic Metamaterial Enclosure for Broadband Low-Frequency Noise Attenuation: Application to Vacuum Pump Noise Control

  • 期刊论文

  • 发表日期：

    2025年11月5日

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  • Nitish Katiyar,
  • Randhir Kumar,
  • Akhilesh Mimani,
  • Shantanu Bhattacharya

摘要

Purpose

Low-frequency noise (LFN) generated by mechanical machines, particularly below 500 Hz, is difficult to mitigate using conventional materials, and prolonged exposure can be harmful to humans. Acoustic metamaterials (AMMs)-based enclosures developed so far typically provide only narrow-band attenuation in this range and face challenges in large-scale implementation. To address these limitations, the present work introduces a simplified enclosure for broadband LFN control from a vacuum pump. The design employs a unit cell comprising a thin elastic synthetic rubber membrane backed by four parallel U-shaped cavities of varying depth, providing effective attenuation without complex geometries or added mass on the membrane, while ensuring scalability for real-world applications.

Materials and Methods

A subwavelength hybrid membrane-type acoustic metamaterial (MAM) was designed and fabricated for broadband LFN attenuation. The unit cell, MU4-AM, comprises a thin synthetic rubber membrane backed by four parallel U-shaped cavities, enhancing thermo-viscous losses and sound absorption (SA). A finite element analysis (FEA)-based parametric study optimized the membrane thickness to maximize normal-incidence SA in the pump’s dominant noise range. The unit cell was fabricated using polylactic acid (PLA) filament with a synthetic rubber membrane, and its acoustic performance was validated in an impedance tube through sound absorption coefficient (SAC) and sound transmission loss (STL) measurements. A full enclosure assembled from MU4-AM cells was further tested for insertion loss (IL) in an anechoic chamber.

Results

The MAM enclosure demonstrated an average IL of 12.2 dB in the 200–600 Hz range. The directivity patterns in both the vertical and horizontal planes exhibited approximately uniform noise attenuation across the microphone angular positions.

Conclusions

The MAM-based enclosure provides a scalable and efficient solution for suppressing noise from a vacuum pump. Its broadband low-frequency performance, combined with a compact and modular design, makes it well-suited for deployment in mechanical rooms, laboratory spaces, and other critical interior environments within buildings. This simplified yet effective approach highlights the potential of MAMs for real-world noise control applications without relying on complex internal structures.