Measurement of Underwater Sound Absorption Coefficient at Variable Hydrostatic Pressures Using an Improved Transfer Function Method

Water-filled impedance tubes are widely used to measure the acoustic properties of underwater sound absorption materials. Traditional transfer function has been applied for sound absorption measurement in air. Because this method needs to switch between two microphones during the test, it is not suitable for a water-filled impedance tube, especially at high hydrostatic pressure. The mounting of the hydrophone is also a challenging problem for water filled impedance at high hydrostatic pressure. In this study, an improved transfer function method is investigated and a new mounting structure is designed for high hydrostatic pressure. Measurements of the sound absorption coefficient of the polydimethylsiloxane material and a water/air interface are used to verify the improved transfer function method, and an underwater sound absorption material is tested under different hydrostatic pressures. Results show that the developed water-filled impedance has a stable and repeatable performance at the working frequency range from 1,500 to 7,000 Hz, and the testing pressure can increase up to 1.5 MPa with suitable reliability. This can significantly improve the measurement efficiency of the underwater acoustic properties of materials and structure at high hydrostatic pressure.