Bandgaps Creation with High Acoustic Losses in Gradient-Based Sonic Crystals

A design of the sonic crystal (SC), called the gradient-based sonic crystal (GBSC), that uses the gradient of properties of the SC array is proposed as an improvement over the traditional design of SCs. The gradient of properties is obtained by changing the resonator dimensions and the distance between them throughout the array instead of keeping them uniform. Because of this non-uniformity, the supercell approximation was used to handle the non-ideal periodic conditions it induces in the array. GBSCs in non-uniform rectangular and triangular lattices were designed and analyzed using the finite element method. The results show that the GBSCs widen existing bandgaps, create new bandgaps, induce high acoustical losses compared to the uniform SCs of Helmholtz resonators (HR) or hollow scatterers (HS) and have similar space requirements. Therefore, the GBSCs can be used for acoustic attenuation in low-mid-high frequency bands. Parameters such as increasing or decreasing order of the resonator size and distance, and the resonator orientation were found to influence the attenuation by the GBSCs. Experiments were conducted on the traditional uniform HS sonic crystals and HR sonic crystals and their finite element (FE) models were developed which were later useful for developing robust FE models of the GBSCs.