Absorption of Broadband Low‐Frequency Sound Beyond the Thermodynamics Limit: An Acoustic Resonator With Magnetic Bearing
Year: 2026
Type: article
Abstract: This study reports the first experimental realization of magnetic negative stiffness to achieve a significant net gain in broadband, low-frequency sound absorption, beyond the thermodynamic limit posed by the relative incompressibility of cavity fluid at low frequencies that otherwise necessitates impractically large absorbers. Analysis based on experimental data demonstrates a fivefold amplification of the absorption bandwidth within the lowest two octaves of human hearing; theoretically, this could be further enhanced with improved structural design and fabrication accuracy. The device employs a magnetic bearing structure with its moving shaft constrained by a mechanical ball bearing, resolving the rotational magnetic instability that otherwise causes significant parasitic stiffness, an issue that has prevented previous designs from succeeding. From an energy perspective, the device creates a potential well where a small incident wave activates a large kinetic response for viscothermal absorption. The proposed magnetic device offers a highly practical and scalable solution for engineering applications.
Source: Advanced Science
DOI: 10.1002/advs.76584
Institution: University of Hong Kong
Language: English
Subfield: Biomedical Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $6,730
OpenAlex ID: W7169103694