Optical detection of the response of liquid jets to internal modulated ultrasonic radiation pressure

Abstract

A liquid jet in air is an acoustic waveguide having a cutoff frequency inversely proportional to the jet diameter. Ultrasound applied to the jet supply liquid can propagate down the jet when the carrier frequency is near-to or above the cutoff frequency. The jet response to the internal acoustic radiation pressure of amplitude modulated ultrasound was monitored along the jet using an optical pseudo-extinction method. The jet profile oscillates at the frequency of the radiation pressure modulation and, where the response is small, the amplitude was found to increase in proportion to the square of the acoustic pressure amplitude as previously demonstrated for oscillating drops [P. L. Marston and R. E. Apfel, J. Acoust. Soc. Am. 67, 27–37 (1980)]. Small amplitude deformations initially grow approximately exponentially with axial distance along the jet. Modulated radiation pressure can be used to stimulate large amplitude deformations and the breakup of the jet into drops. [Work supported by NASA.]