Two-Dimensional Measurement of Airborne Ultrasound Field Using Thermal Images

Recently, the applications of airborne ultrasound technology have garnered considerable attention; however, high-speed ultrasound field measurements in air have not been well researched. This study demonstrates that thermal responses to high-intensity airborne ultrasound can be used to visualize air-borne ultrasound fields. Thermal images on a mesh screen enable the rapid quantitative measurement of two-dimensional ultrasound fields. Additionally, based on the temperature distribution on a surface that reflects ultrasound waves, it is possible to determine the ultrasound focus position with a resolution much finer than the wavelength. The results demonstrate that thermography observations based on ultrasound -temperature conversion, which are conventionally time-consuming or difficult to perform, can be used to visualize acoustic fields within 0.5 s. These findings will advance engineering applications that use strong airborne ultrasound, such as midair haptics and acoustic levitation, and provide scientific and tech-nical applications for detecting surface properties and composition, including those of cells and fragile materials.