A Helmholtz Resonator-Based Acoustic Metamaterial for Power Transformer Noise Control

Controlling low-frequency noise propagated by power transformers in urban and industrial areas poses a technical challenge in the design of sound absorbers. Although existing acoustic metamaterials are largely successful as single-band absorbers, they are far from optimal approaches to absorb power transformer noise. As a common method of providing multi-band absorbers, the parallel configuration of multiple individual units leads to the coupling effect, resulting in the absorption coefficient drop. In this research, a novel design is proposed to convert a single-band Helmholtz resonator-based sound absorber into a multi-band absorber while maintaining its thickness at 55.1 mm, similar to 1/62 of 100 Hz noise wavelength. The proposed design offers simultaneous perfect absorptions at 100, 200 and 300 Hz frequencies as main components of power transformer noise. Design validation is carried out using finite element modelling in COMSOL Multiphysics and the experimental analyses on the 3D-printed sample.