Liu Yaoguang, Liu Xiandong, Xu Jun, Hu Xiaojun, Xia Zhaowang
School of Transportation Science and Engineering, Beihang University, Beijing 100191, People's Republic of China.
School of Energy and Power Engineering, Jiangsu University of Science and Technology, Zhenjiang 212003, People's Republic of China.
J Acoust Soc Am. 2017 Jul;142(1):72. doi: 10.1121/1.4990521.
A method to characterize the porous parameters (i.e., tortuosity, flow resistivity, viscous, and thermal lengths) of double-layered poroelastic structures is proposed and validated. The porosity, elastic coefficients (estimated), frame density, and thickness of each layer are assumed to be known. The way is to first identify the effective density and bulk modulus of each layer by a system of equations established based on the measured surface impedance of the structures backed by various air cavities, and then extract the porous parameters from the above identified parameters through the least square method at frequencies where the effect of vibration of frame is trivial. Because of the insensitivity to the surface impedance and the negligibility of the thermal loss compared to the viscous dissipation, the two acoustical bulk moduli are assumed to be identical. Two double-layered structures are constructed, which parameters are identified by the proposed method, and further verified by experiments. Simulations show that for double-layered structures constructed by materials with large frame density (viscous length) or small flow resistivity, the identified precision would be better. In addition, because of the identical assumption, the ratio of two thermal lengths should not exceed two or be less than one half.
