Study for Contactless Detection of Number of Thin Sheet Material by Sound

本文介绍了一种非接触检测多孔材料薄片数量的新方法。有必要检测一张或多张纸张，以避免处理不当。该检测传感器利用整个声学系统内传递函数的相位或幅度的变化。多孔材料的入射阻抗随板数的不同而不同。特性声阻抗和复波数定义了材料的特殊特性。在这种应用中，了解多孔材料的特性阻抗是有用的。理论分析和有限元分析都包括了传递函数法测得的薄板阻抗。实验结果、理论分析和有限元结果吻合较好。在下一部分中，可以计算不同颗粒直径和任意厚度的多孔多层膜的垂直入射吸收系数。这种计算过程比较长，所以对实际多层膜的实验和计算进行了比较。计算结果与实验结果相吻合。因此，不同粒径之间多层膜的垂直入射吸收系数的计算结果是有用的。湿度是影响多孔材料声学特性的重要因素。因此，我们还研究了颗粒(作为多孔)材料的含水率与吸收系数之间的关系。在上一个研究阶段，我们开发了一套包括4个麦克风的阻抗管系统来测量多孔薄膜的传输损耗。

This report deals with the development of a new method for detecting the number of thin sheets of porous material without making contact. It is necessary to detect one or more of sheets to avoid mishandling. This detecting sensor utilizes the variation of the phase or magnitude of the transfer function within an entire acoustic system. The incident impedance of the porous material varies with the number of sheets. Characteristic acoustic impedance and complex wave number define the particular characteristics of the material. In this application it is useful to know characteristic impedance of the porous material. The measured impedance of sheets by the transfer function method was included in the theoretical analysis and FEM analysis. The results of the experiments, theoretical analysis and FEM show good coincidence.In the next part, the normal incidence absorption coefficient for porous multilayer between different grain diameters with arbitrary layer thicknesses can be calculated. This calculation process is comparatively lengthy, so the experiments for real multilayer and the calculations were compared. Result of the calculations agreed to the experiments. Consequently, calculation result of normal incidence absorption coefficient for multilayer between different grain diameters is useful.Moisture is an important affector for acoustic characteristics of the porous materials. So we investigated also about relationship between percentage of moisture content and absorption coefficient of granular (as porous) material.In the last research period we developed a system including an impedance tube with 4 microphones to measure transmission loss of porous thin film.