Measurements of Sound Pressure Distribution of Focused Ultrasound Beams Using a Thermal Imaging Technique

Abstract

The present study investigates the characteristics of a phased-array ultrasound unit as a flow control actuator. Acoustic streaming is driven by the intense ultrasound through the viscosity. The ultrasound phased array unit AUTD3, which consists of many ultrasound transducers arranged in a rectangular shape, can generate various focused ultrasound fields, e.g., the Bessel and focused beams, and the beam parameter can be configured. The Bessel and focused beams were evaluated using thermal imaging measurements. The mesh screen was exposed to the ultrasound beam, and the intensity of sound pressure fluctuations was evaluated from the instantaneous temporal temperature gradient at the sound emission. The three-dimensional spatial distributions of the sound pressure fluctuations in the beam were evaluated at different distances between the ultrasound transducer unit and the mesh screen. It was revealed that the focused beam produced a maximum sound pressure of 4.49 kPa at the focal point. The Bessel beams showed strong sound pressure fluctuations, i.e., exceeding 2 kPa at the beam center, in a wide range of distances.