Active Noise Reduction Technology

Noise levels in crew compartments below the flight decks on Navy ships during flight operations have traditionally been extremely noisy due to jet engine noise as well as launch machinery transients. Levels exceed Navy desired levels by over 10 dB. Current state of the art materials do not work well at low frequencies. SSC proposes to develop an active noise solution that consists of a modular, fully integrated smart material that can be applied to the interior compartments of ships. The smart acoustic panel will reduce radiating noise by employing advanced smart materials such as polyvinylidene fluouride (PVDF) and lead zirconate titanate (PZT) actuation materials, embedded MEMs based acoustic and vibration sensors, and polyurethane foam for passive vibration absorption. A method to use smart acoustic materials to provide local noise control of manned spaces will also be investigated if global control proves to be unfeasible.

Benefits of this project include: devlopment of acoustic smart panels and quiet zone generation will enhance habitability on aircraft, and in high noise manufacturing areas. It will also enhance vehicle stealth applications.

Battlefield Acoustics

We are developing noise cancellation software for use in Army battlefield robotics. This software will eliminate unwanted signals from microphones mounted on an unmanned vehicle. We have recently tested our system on the Demo III Experimental Unmanned Vehicle (XUV) built by General Dynamics Robotic Systems Technology. Our noise cancellation software achieved over 40 dB narrowband cancellation while eliminating over 30 tones from the robots' background noise level.

Some of these results are presented in the Air Coupled Sensor Workshop Presentation Slides (Adobe Acrobat PFD Format 437 KB)

Active Noise Control for Smart Materials

We have been developing active noise cancellation systems for acoustic composite tiles for several years. We have developed a real-time 48 channel controller using programmable DSPs. This system was integrated into a smart skin that was demonstrated underwater. Our control system designs are based on hierarchical approaches. We are currently investigating on-line evolutionary techniques for fully adaptive control systems that change sensor and actuator configurations as well as filter coefficients. These systems promise to define the state of the art in affordable and effective controllers for intelligent materials.

We are currently developing an 80 channel active noise control system using programmable DSPs networked together. The active noise control system contains processing resources with over 16 Billion Operations Per Second capability.

A related publication is: L. Riddle and J. Murray, 'Smart Structure Active Sonar Echo Cancellation Using Frequency Scheduled Control, presented at the 1998 SPIE Conference on Smart Materials, (Postscript File)

A technical review of our progress appears in the Smart Skin Demonstration Presentation Slides (Adobe Acrobat PFD Format 159 kb)

A full length paper describing the trade-offs involved in making a cost effective ANC system for complex problems is described in:

L.Riddle, J. Murray and S. Lease, 'Active Noise Control Architecture for the Smart Skin Demonstration,' ACTIVE-99, International Symposium on Active Noise Control, Dec 2-4, 1999.

New: We have developed a new MATLAB™ based Active Noise Control Simulation Toolbox. The simulation offers finite element modeling interfaces, sensor, filter and hardware models, and state-of-the-art multi-channel adaptive LMS algorithms.