Estimating characteristic lengths by combining direct measurements and the Kozeny-Carman relation

This work revisits an indirect characterization method that exploits visco-inertial and thermal frequency response functions to estimate the macroscopic parameters of fibrous media [Panneton and Olny, J. Acoust. Soc. Am. 119, 2027-2040 (2006); Olny and Panneton, J. Acoust. Soc. Am. 123, 814-824 (2008)]. In practice, this method faces major challenges for highly resistive materials because the transition frequencies fall outside the measurable range of the standing-wave tube. To overcome this limitation, an alternative approach combining the equivalent characteristic-length relation derived from ultrasound measurements with a Kozeny-Carman-type relation is proposed. The methodology and its validation on resistive felts demonstrate improved estimation of viscous and thermal characteristic lengths from measurable parameters.