Acoustic stealthness by reasonant ribs – FARAON

The FARAON research project aims to study and validate a device which consists in attaching to a part of the stiffeners of a metallic structure, resonant systems which characteristics randomly vary from a system to another one. These systems will locally modify the vibrations of the structure at their resonant frequencies, thus creating a random frequency dispersion of the diffracted sound field. The acoustic field diffracted by the periodic stiffeners is blurred and attenuated so that the structure becomes stealth at low and very low-frequency. FARAON also proposes to define optimum devices to make stealth a metallic cylindrical shell at very low frequency in operational conditions.

This research project is motivated by the very promising results obtained through first calculations based on a theoretical formalism that gives the acoustic field diffracted by a ribbed finite cylindrical shell with axisymmetric oscillators [1]. These results show the possibility of realizing devices that make stealth a target and having relatively small thicknesses at very low-frequency.
To reach this ambitious objective, the FARAON project is divided into 3 workpackages. The selection of the shape of the structure and the classic or metamaterials for the resonant system, is performed in the first workpackage. The theoretical and experimental validity of the device is made in the second workpackage with metallic plates in air and in water. Finally theoretical models are elaborated from the results obtained previously, to define the optimal device for a metallic finite cylindrical shell at low and very low-frequency in the last workpackage.
This research project is related to the subject of the axis N°3 « Ondes acoustiques et radioélectriques» and « Propagation pour les sonars en ultra basses fréquences », « Détection et Imagerie pour systèmes radar /sonar ».
The project is led by Thales Research and Technology, which has an expertise in material and in target strength modelling, with the support of IEMN for the selection of the resonant structure and the measurements of vibrations, LOMC for the manufacturing of samples and the acoustic tests in tank and TUS for the finite elements modeling and for its expertise in Underwater Acoustics.