Broadband noise-insulating periodic structures made of coupled Helmholtz resonators

Acoustic metamaterials and phononic crystals represent a promising platform for the development of noise-insulating systems characterized by a low weight and small thickness. Nevertheless, the operational spectral range of these structures is usually quite narrow, limiting their application as substitutions of conventional noise-insulating systems. In this work, the problem is tackled by demonstration of several ways for the improvement of noise-insulating properties of the periodic structures based on coupled Helmholtz resonators. It is shown that tuning of local coupling between the resonators leads to the formation of a broad stopband covering similar to 3.5 octaves (200-2100 Hz) in the transmission spectra. This property is linked to band structures of the equivalent infinitely periodic systems and is discussed in terms of bandgap engineering. The local coupling strength is varied via several means, including introduction of chirped structures and lossy resonators with porous inserts. The stopband engineering procedure is supported by genetic algorithm optimization, and the numerical calculations are verified by experimental measurements.