| Anechoic coating is crucial to the submarine stealth technology and is a major part of quiet-submarine design .In this paper, the main work is as follows: the comprehensive narration about the measurement of acoustic properties in-duct; the concept of impedance method arise to overcome the shortcomings in present method; a lot of research in measuring the impedance of anechoic coating; research in using impedance method to count reflection ratio and sound reduction index of the anechoic material; lots of experiments on the samples of coating which have certain structure inside; evaluation on anechoic coating laid on the true submarine by the mentioned impedance method.In the whole research process, the conventional measuring method is improved. The input impedance and the transfer impedance of anechoic coating are measured under different temperatures and pressures. The coating's acoustical behavior is evaluated quantitatively by inputting acoustic impedance and transfer impedance, and then the reflectance under specific backings is calculated by the result. It efficiently resolved the influence due to the selection of backing in traditional method. At the same time, a special verification experiment is designed; it can verify not only the result of impedance dependability, but also the feasibility of impedance method.While the theoretical investigation, submarine hull coated with anechoic coating is assumed to be planar multi- layers system: the superficial layer is the anechoic coating; the steel plate is for the base (as in the case of a single-hull submarine) or two steel sheets with a water layer sandwiched between them (as in the case of a double-hull submarine). The model surface' acoustic impedance is calculated by analytical method. Then combining with the experimental results, we have done a lot of research on acoustic properties of the coating.This paper begins from impedance of anechoic coating, includes a large...
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