Broadband structural acoustic silencers

Abstract

It has long been a goal of the noise control community to achieve broadband passive attenuation of sound propagating in waveguides. By using designs based on models of the mammalian cochlea, theoretical studies show that a structural-acoustic silencer can achieve the desired broadband transmission loss and anechoic termination is possible provided sufficient losses are present. The mammalian cochlea can be idealized as a compact rectangular duct system (2.5×0.1×0.1 cm) interacting with a strongly orthotropic plate of variable impedance (known as basilar-membrane). A coupled fluid-structure pressure-displacement wave propagates along the basilar-membrane resonating at a frequency-dependent location. In this process, the wave is attenuated with an accompanying reduction in duct pressure (nearly 100 dB over 20–20<th>000 Hz for humans). Current research intends to imitate this aspect of cochlear behavior for reducing noise level in pipes. Possible applications include use in automotive mufflers and quieting hydraulic systems. Design of fluid/structure interaction between the orthotropic plate and duct is based on numerical modeling using the 2.5-D finite element/analytic technique. Results based on interaction of a varying thickness plate made of typical orthotropic materials like unidirectional graphite-epoxy composite, with fluids like water and oil, are presented. Comparison is made against a constant thickness plate made of the same material.