Interferences between Bandgap and Resonances in Locally Resonant Sonic Materials

The use of Helmoltz resonators has been a classic solution for the control of acoustic wave transmission over the years. One of the most analyzed devices in the last decade is formed by arrays of these resonators, usually called Locally Resonant Sonic Materials, one of whose main applications is the development of acoustic screens with high technological value. There are two main waves control mechanisms that appear in these devices: resonances and bandgaps, due to the multiple scattering that appears because the Helmholtz resonators are ordered forming an array. But the manipulation of both phenomena is not always easy. When the resonance peaks are far enough away from the band gap (BG) in the frequency range, the coexistence of the two phenomena occurs without interferences. However, when both peaks are very close to each other, some phenomena of interference between the two mechanisms appear. In this work we present the cases in which the phenomenon of resonance-BG interference occurs, including its physical explanation and some possible solutions to control it. Although this work is developed for audible, the conclusions can be applied to any device designed for any frequency range.