Compact Metamaterial Micro-Slit Panel Absorbers for Low-Frequency Tonal and Broadband Noise Control

Abstract

This study proposes a novel compact micro-slit panel absorber (C-MSPA) designed to improve low-frequency noise absorption while conserving material and space. The C-MSPA utilizes optimized slit and air cavity geometry, achieving reduced panel thickness and greater cavity depth for enhanced acoustic performance. Analytical models are developed to predict C-MSPA performance and validated via numerical simulations and impedance tube measurements. Three analytical impedance models are compared to refine the sound absorption predictions, and parametric studies assess the influence of slit width, panel thickness, and air cavity depth. Optimization techniques integrating analytical models are applied to maximize C-MSPA performance. Additionally, 3-D finite element analysis (FEA) simulations examine sound absorption under normal and grazing incidence sound waves, corroborated by experimental data in an impedance tube. Testing with an 80 mm counter-rotating (CR) fan (nominal speed of 12000/11300 RPM, axial-flow Mach number of 0.047), commonly found in data center servers, shows that C-MSPAs achieve superior noise reduction compared to hardwall and industrial acoustic foam setups, with over 6 dB reduction at target frequencies of 600 Hz, 1200 Hz, and 900–1800 Hz versus a hardwall, and more than 1.5 dB versus standard industrial acoustic foam. C-MSPAs minimally impact aerodynamic performance, with only a 0.5% deviation from the baseline P-Q curve. These results highlight C-MSPAs as effective noise control solutions for CR fans in compact electronics cooling applications, providing significant noise reduction without compromising airflow performance.