Urban Air Mobility is reshaping the skies above our cities, but at a cost we are only beginning to understand. While electric propulsion has eliminated many traditional emissions, the intense tonal noise generated by eVTOL rotors poses a new environmental challenge for densely populated areas. This thesis presents an innovative solution: a compact, low-cost acoustic metamaterial capable of dramatically reducing intense tonal noise. Built from modular hexagonal cavities that can be tuned through simple or complex internal connections, the design achieves exceptional sound absorption despite its thin profile. Numerical simulations, impedance tube experiments, and diffuse field testing reveal absorption peaks far below those predicted by traditional acoustic limits-up to an 80% reduction in resonance frequency. Wind tunnel tests at TU Delft further validate the metamaterial's performance under realistic conditions, including flow and propeller-generated sound. This work opens the door to quieter urban skies, offering a practical path toward reducing the acoustic footprint of next generation aerial vehicles.