Phononic crystal sandwich for broadband and low frequency acoustic insulation under diffuse field

Light and thin structures exhibiting high sound insulation over a wide frequency range are a major industrial concern, especially in the transport and building sectors. Phononic crystals constitute promising solutions to solve this issue due to their particular dispersion properties. In this work, we build a system consisting of a well-known sandwich panel comprising a soft elastic core layer hosting periodically arranged rigid inclusions. Diffuse field measurements show a huge improvement of the Transmission Loss compared to the system without inclusions. In fact, for this kind of panel, the structured core enables Bragg band-gap opening for guided slow propagating waves leading to low frequency and broadband enhancement of the Transmission Loss. Using a 3cm-thick material we are able to improve the response from 300 Hz on (λ/38 in air). We then develop a finite elements model to achieve a precise description and understanding of the problem. We also propose a numerical tool to analyze the system's band-structures from a vibroacoustic point of view. It proves very useful for the further development of practical solutions.