Flexible light-weight multi-element/multi-path structures to reduce noise and vibration

Sound and vibration transmission can be reduced by dividing a structural barrier into several constituent subsystems with separate, but coupled, wave transmission paths. Multi-element/multi-path (MEMP) structures utilize the inherent dynamics of the system, rather than damping, to achieve substantial reduction over a wide frequency range, while satisfying constraints on static strength and weight. The higher order and increased complexity of MEMP structures afford a wealth of opportunities for vibration and noise reduction, but the approach requires rethinking the structural design process. Simulations show the existence of robust solutions that provide surprisingly large wide-band reductions. Attenuation is achieved through a variety of processes acting in concert: different subsystem wave speeds, mixed boundary conditions at attachment points, interaction through elastic couplings, cross-coupling of applied forcing, and cross-communication between subsystems to modify acoustic radiation. The dynamics of the air between the layers of an MEMP barrier, particularly how the structure is ventilated to achieve acoustic cross-communication, can strongly affect performance and is an important issue in the modeling and design. Preliminary experimental results show that the concept is practical and promising, and may have application in automotive and aerospace vehicles.