Abstract
The transfer function method is a common method for establishing a traveling wave field in a sound tube to measure the reflection and transmission coefficient of underwater material. The voltage applied to the secondary sound source can be calculated in accordance with the transfer matrix between the sound sources and hydrophones, then a traveling wave field can be established in the sound tube. However, the transfer function must be remeasured when the measurement frequency needs to be changed. A checking procedure of the traveling wave field in the sound tube is essential before measuring underwater acoustic material. If it is not an accurate traveling wave field, the secondary sound source signal should be corrected until the traveling wave field meets the requirements. To address these problems, an adaptive control method for generating plane traveling waves is proposed. The phase difference of sound pressures measured using the two hydrophones between the secondary sound source and the sample is used as the objective function in the adaptive algorithm, and the amplitude and phase of the secondary sound source can be obtained using the adaptive control system in the frequency domain. When a traveling wave field is formed, the reflection and transmission coefficient of the sample can be measured at the same time. With this method, the procedure of testing the traveling wave field is omitted. If the state of the primary sound source changes, the signal form of the secondary sound source can be changed immediately. Therefore, the efficiency of material measurement is improved. Theoretically, this method can obtain the most matching signal form of the secondary sound source, such that the accuracy of this method is remarkably high. Simulation and experimental results in this paper show that the measurement accuracy is reliable within the frequency range of 100–2500 Hz.
Highlights
The performance parameters of underwater material, such as the anti-acoustic baffle and anechoic tile, are significant, and the measurement parameters that reflecting its acoustic performance are the reflection and transmission coefficient of the sample under the plane wave perpendicular to the incident
The wavelength in water becomes longer with the frequency decreasing, which cause it is difficult to measure and remove the reflected wave from the end of the sound tube with traditional methods, so the reflection coefficient and transmission coefficient of the underwater material at low frequencies cannot be accurately measured
This work proves that the adaptive control termination of an sound tube can help form traveling waves downstream of the tube, and the reflection and transmission coefficients of sample can be calculated automatically and accurately
Summary
The performance parameters of underwater material, such as the anti-acoustic baffle and anechoic tile, are significant, and the measurement parameters that reflecting its acoustic performance are the reflection and transmission coefficient of the sample under the plane wave perpendicular to the incident. Accurate measurement of the complex reflection and transmission coefficient of underwater materials is important in the field of underwater acoustic engineering [1,2]. A primary sound source in the upstream section excites incidence waves, transmits them to the downstream section after passing the test sample, and meets the boundary condition in the form of acoustic load. Incidence and reflected waves are formed on the left (A and B) and right (C and D) hands of the test sample, respectively.
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