Locally Resonant Metamaterial Patches on Rear Shock Towers of a Vehicle to Reduce Structure‑Borne Road Noise: Numerical and Experimental Performance Validation

Over the past decades, automotive companies have sought lightweight and performant noise, vibration and harshness (NVH) solutions to comply with stringent regulations for CO₂ emissions and noise pollution. Combining lightweight design with improved NVH solutions is often a challenging task: low mass and high stiffness materials are generally characterized by poor NVH behavior and low noise and vibration levels often require heavy and bulky additions, especially to be effective in the low frequency regime. To face this challenge, recently, locally resonant metamaterials (LRMs) have come to the fore. These materials combine in one solution lightweight design and superior noise and vibration attenuation performance, beating the mass law in tunable frequency ranges, referred to as stop bands. The LRM concept is used in this work to tackle a low frequency structure borne road noise problem in a commercial vehicle. A LRM solution is applied on the rear shock towers of the vehicle, with the goal of attenuating the vibrational energy entering into the vehicle body through the suspension assembly, which is excited by the interaction of the tire with the road while driving. This results in a reduction of the noise in the interior compartment around 190 Hz. In order to benchmark the performance of the LRM concept, a vehicle is chosen which is sold with a tuned vibration absorber installed on each of the rear shock towers as NVH solution. Each of the tuned vibration absorbers (TVAs) adds 1.46 kg of mass to the vehicle. The LRM concept is designed to reduce the mass of the current solution by 48% and to have similar NVH performance. The LRM concept is realized through additive manufacturing and it is added as patches on the rear shock towers to replace the TVAs. Both numerical and experimental results in lab and on a smooth road profile validate the performance of the LRM concept proposed.