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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.

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In order to predict acoustic pressure distributions by exterior incident wave at Cylindrical Hydrophone Array (CHA) sensor's positions, acoustic pressure analysis is performed by using beam tracing method. Beam tracing method is well-known of reliable pressure analysis methods at high-frequency range. When an acoustic noise source is located at the center of rectangular room, acoustic pressure analysis is performed by using both beam tracing method and Power Flow Boundary Element Method (PFBEM). By comparing with results of beam tracing method and those of PFBEM, the accuracy of beam tracing method is verified. We develop the CHA pressure analysis program by verified beam tracing method. The developed software is composed of model input, sensor array creator, analysis option, solver and post-processor. We can choose a model option of 2D or 3D. The sensor array generator is connected to a sonar which is composed of center position, bottom, top and angle between sensors. We also can choose an analysis option such as analysis frequency, beam number, reflect number, etc. The solver module calculates the ray paths, acoustic pressure and result of generating beams. We apply the program to 2D and 3D CHA models, and their results are reliable.

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