ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

1pNS13. A multi-mode acoustic filter based on Bragg resonance.

Muhammad A. Hawwa

Chris R. Fuller

Ricardo A. Burdisso

Vib. and Acoust. Labs., Dept. of Mech. Eng., Virginia Polytech. Inst. and State Univ., Blacksburg, VA 24061-0238

A unified method is proposed to suppress duct acoustic waves. According to this method, a circular cylindrical duct is designed to have a geometric periodicity at its wall in order to act as a wave filter. The filter action of the periodic rigid wall is based on the mode coupling occurring under the Bragg condition resulting in a strong stopband interaction. The problem is attacked using the perturbation method of multiple scales, leading to the derivation of the coupled-mode equations. The performance of the duct as a wave attenuator is presented in terms of the reflection coefficient or the transmission loss factor. Due to the nature of the dispersion curves of the cylindrical duct, many modes could share the same stopband. Hence, a multi-mode acoustic filter could be designed over a certain frequency band. This theoretical study might provide a basis for design concepts of acoustic silencers.