Spatio-temporal measurement of underwater ultrasound field using non-contact technique

We successfully measured the spatio-temporal ultrasound acoustic field in water using Background-oriented schlieren (BOS) technique. Other the ability to obtain the 3D-pressure field easily and quickly, BOS needs only a background image and a camera to measure the pressure field without disturbing the flow field. To discuss the measurement accuracy of BOS, we compared its results with the measurement performed using a hydrophone, which is a contact measurement technique. BOS demonstrated good agreement with the hydrophone and theoretical values at a given wavelength and period. The spatio-temporal acoustic field measured by BOS showed that the reflected ultrasound from the hydrophone changed the acoustic field. Especially, BOS could visualize the influence of the shape and size of hydrophone sensor on the propagation of reflected wave and acoustic field. This BOS technique can also measure the acoustic field of other multiphase flow.