Reconstruction of Three-Dimensional Sound Field from Two-Dimensional Sound Field Using Optical Computerized Tomography and Near-Field Acoustical Holography

We propose a method for reconstruction of a three-dimensional sound field using optical computerized tomography (O-CT) and near-field acoustical holography (NAH). The center of a transducer is the origin, and a sound wave is radiated along the z-axis. An ultrasonic wave affects the phase of light passing through the sound field, and the phase change is determined using a Michelson interferometer. Projections of the underwater sound field were obtained by mechanical scanning, and the sound field was reconstructed from 18 of these projections by O-CT. To determine sound velocity for reconstruction of the three-dimensional sound field, two-dimensional sound fields at z = 40 and 41 mm were reconstructed using O-CT in a region of 28 ×28 mm². The sound velocity was determined to be 1508 m/s using inverse analysis of NAH. Using NAH and the determined sound velocity, the three-dimensional sound field of 28 ×28 ×5 mm³ was reconstructed from the two-dimensional sound field at z = 40 mm. The sound field reconstructed using NAH was in good agreement with the sound field reconstructed using O-CT.