The Measurement Of Reflection Coefficient Of Underwater Acoustic Materials With Broad-band In Free Field

Nowadays, the absorbing materials are widely used to reduce noise. The reflection coefficient indicate the absorbing characters of the absorbing materials with number, it can guide appliance of the absorbing materials and has an important significance in acoustic design. So how to measuring reflection coefficient effectively is arose much attention.This paper is studied about measuring reflection coefficient with vector hydrophone in free field. First of all, the theories of the surface impedance and asymptotic solution are explained, the characteristic of sound field which is brought by monopole is analyzed specially. The formula for reflection coefficient when plane wave or spherical wave incident are presented; some simulation by matlab have been done when spherical wave incident in free field. The second, finding the relationship of reflection between the monopole incident at near field and far field. The third, learning about cepstrum analysis to get the reflection coefficient.For the purpose of precision result, the measuring error and calculation error of the complex reflection coefficient from surface impedance method are discussed and simulated. The numerical analysis is used to discuss the influence of the distance among the sound source, the hydrophone and the material which is to be measured and the influence of the calculation error. The measurement system based on the surface impedance is founded. It is proved the feasibility of the surface impedance method with experiment, the experiment have been done include several incidence angle and basic frequencies, the measuring result is satisfying and texting the conclusions from the simulations.The surface impedance method make use of the vector hydrophone can measuring the pressure and particle velocity at the same time decreased the experimental time, making the experiment more easier and needed few equipment, it is fit for measurement in situ. The vector hydrophone have the advantage of direction and measurement in low-frequency make the measuring frequency lower, and the vector signal processing is also useful in measuring the reflection coefficient.