An inverse measurement of acoustic impedance of porous woven hoses in engine intake systems

摘要

A porous tube, comprised of a resin-coated woven fabric has recently been used as an effectivecomponent for use in intake systems of internal combustion engines to reduce the intake noise. Inorder to predict the acoustic performance of an intake system with a porous duct, information onthe acoustic wall impedance is essentially required. However, the accurate measurement of wallimpedance has not been easy because of its peculiar acoustical and structural characteristics thatare involved with very high resistance, thickness, curvature, and inhomogeneity. Although theresistance estimation method using the measured reactance, by using a concentric measurementlayout, and transmission loss was proposed, the method was quite cumbersome because it needstwo-stage measurement and the resistance estimation process. In this paper, a new measurementtechnique is presented, which inversely calculates the acoustic impedance from the measuredtransmission coefficients of several specimens of equal porosity. The pressure transmissioncoefficient is expressed by the four-pole parameters of transfer matrix and the acoustic impedanceis obtained iteratively from the fitting model of transmission coefficient. The developed techniquecan measure the acoustic impedance of porous woven hoses more precisely and easier than before.A good agreement between predicted transmission loss using the measured impedance and themeasured TL data.