Radiation pressure deformation of fluid and elastic objects and applications: Overview and selected recent focused-traveling-wave experiments

Low-frequency (LF) shape oscillations of levitated drops in water having amplitudes proportional to the square of the applied ultrasonic pressure were demonstrated by Marston and Apfel [J. Acoust. Soc. Am. 67, 27–37 (1980)]. The LF-resonant drop response and scaling were consistent with the spatially distributed modulated radiation pressure (MRP) of the applied double-sideband-suppressed-carrier ultrasound (DSSCU). The response was measured using light scattering. Related early developments including drop and bubble fission and reduce-gravity applications are noted in [J. Acoust. Soc. Am. 156, 1586–1593 (2024)]. Subsequent experiments concern resonant responses of elastic objects in DSSCU beams in water having short focal lengths H of about 15 cm. Recently, the measurements of LF-sound radiated by the elastic objects were extended to beams with H of 1 and 1.5 m. The radiated LF-acoustic pressure is proportional to the square of the DSSCU-source drive voltage. In some situations, the LF-mode shapes have been inferred by scanning the focal location along the elastic object. Specular reflection of the ultrasound contributes significantly to the MRP [J. Acoust. Soc. Am. 149, 3042–3051 (2021)] when the elastic objects are large in comparison to the ultrasonic wavelength. [Research supported by the US Office of Naval Research.]