Dynamic impedance matching for active noise control in a cylindrical waveguide

In this paper, the feasibility of dynamic impedance matching for noise reduction in a cylindrical waveguide is demonstrated. An active acoustic coating, inserted parallel to the direction of wave propagation, is assumed to dynamically match the acoustic impedance of the incoming wave. The active coating appears as an acoustic branch containing the same fluid, and therefore part of the incoming wave can be diverted to and dissipated in the coating. The performance of the active coating is evaluated using a finite element analysis, where the coating is modeled as a dynamic impedance matching boundary. Simulations reveal that significant reductions in the downstream acoustic pressure can be achieved. Unlike the conventional active techniques that employ phase cancellation, dynamic impedance matching has a number of advantages such as a relatively low power requirement.